javaweb发展历程

简介

1995年java语言的诞生，刚好赶上了网络时代，java三大军：JavaSE（桌面程序），JavaME（手机端），JavaEE（web服务器），由于java在桌面程序和手机端的开发，都赶不上其他语言写的好，很快阵亡，然而发现，java简直就是为服务器而生的语言，由于项目都是发布在linux服务器上的，而java很重要的特性就是与平台无关性，因为java程序都是用在java虚拟机上运行的，所以不管是什么平台，只要安装了jvm就可以运行java程序，做到了一次编译，到处运行（Write Once,Run anyway），所以java语言很快就占领了web市场。javaweb就是用java语言编写的web应用，最开始开发初期，sun公司（现在已被Oracle公司收购）推出了Servlet技术，提供了开发web应用的基础，下面感受一下servlet

package com.hut.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 类说明
 *
 * @Author 茶茶
 * @Create 2020-04-23 21:27 新建
 */
public class HelloServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter out = resp.getWriter();//获得响应流
        out.println("Hello,Servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }

}

写好了自己的servlet类之后，只需要将该servlet类注册到web容器里，也就是web.xml里

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

<!--    注册Servlet-->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.hut.servlet.HelloServlet</servlet-class>
    </servlet>
<!--    Servlet的映射路径-->
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

</web-app>

可以看见在web.xml注册了该HelloServlet类，并去了个名字叫做hello，再将该servlet映射到/hello请求，这样客户端只要发送/hello请求，就能找到该servlet类执行相应的代码，这就是一个简单的servlet。然而大型的web应用，都对应了很多的servlet类执行各种各样的请求，下面请欣赏一下下面的代码，简单看看就好，主要是看一下恶心程度（删除了部分代码）

package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {

      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("<!DOCTYPE html>\r\n");
      out.write("<html lang=\"en\">\r\n");
      out.write("    <head>\r\n");
      out.write("        <meta charset=\"UTF-8\" />\r\n");
      out.write("        <title>");
      out.print(request.getServletContext().getServerInfo() );
      out.write("</title>\r\n");
      out.write("        <link href=\"favicon.ico\" rel=\"icon\" type=\"image/x-icon\" />\r\n");
      out.write("        <link href=\"favicon.ico\" rel=\"shortcut icon\" type=\"image/x-icon\" />\r\n");
      out.write("        <link href=\"tomcat.css\" rel=\"stylesheet\" type=\"text/css\" />\r\n");
      out.write("    </head>\r\n");
      out.write("\r\n");
      out.write("    <body>\r\n");
      out.write("        <div id=\"wrapper\">\r\n");
      out.write("            <div id=\"navigation\" class=\"curved container\">\r\n");
      out.write("                <span id=\"nav-home\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Home</a></span>\r\n");
      out.write("                <span id=\"nav-hosts\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Documentation</a></span>\r\n");
      out.write("                <span id=\"nav-config\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("config/\">Configuration</a></span>\r\n");
      out.write("                <span id=\"nav-examples\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatExamplesUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Examples</a></span>\r\n");
      out.write("                <span id=\"nav-wiki\"><a href=\"https://wiki.apache.org/tomcat/FrontPage\">Wiki</a></span>\r\n");
      out.write("                <span id=\"nav-lists\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html\">Mailing Lists</a></span>\r\n");
      out.write("                <span id=\"nav-help\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("findhelp.html\">Find Help</a></span>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"asf-box\">\r\n");
      out.write("                <h1>");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageContext.servletContext.serverInfo}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("</h1>\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"upper\" class=\"curved container\">\r\n");
      out.write("                <div id=\"congrats\" class=\"curved container\">\r\n");
      out.write("                    <h2>If you're seeing this, you've successfully installed Tomcat. Congratulations!</h2>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"notice\">\r\n");
      out.write("                    <img src=\"tomcat.png\" alt=\"[tomcat logo]\" />\r\n");
      out.write("                    <div id=\"tasks\">\r\n");
      out.write("                        <h3>Recommended Reading:</h3>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("security-howto.html\">Security Considerations How-To</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("manager-howto.html\">Manager Application How-To</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("cluster-howto.html\">Clustering/Session Replication How-To</a></h4>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"actions\">\r\n");
      out.write("                    <div class=\"button\">\r\n");
      out.write("                        <a class=\"container shadow\" href=\"/manager/status\"><span>Server Status</span></a>\r\n");
      out.write("                    </div>\r\n");
      out.write("                    <div class=\"button\">\r\n");
      out.write("                        <a class=\"container shadow\" href=\"/manager/html\"><span>Manager App</span></a>\r\n");
      out.write("                    </div>\r\n");
      out.write("                    <div class=\"button\">\r\n");
      out.write("                        <a class=\"container shadow\" href=\"/host-manager/html\"><span>Host Manager</span></a>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"middle\" class=\"curved container\">\r\n");
      out.write("                <h3>Developer Quick Start</h3>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("setup.html\">Tomcat Setup</a></p>\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("appdev/\">First Web Application</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("realm-howto.html\">Realms &amp; AAA</a></p>\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("jndi-datasource-examples-howto.html\">JDBC DataSources</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatExamplesUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Examples</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"https://wiki.apache.org/tomcat/Specifications\">Servlet Specifications</a></p>\r\n");
      out.write("                        <p><a href=\"https://wiki.apache.org/tomcat/TomcatVersions\">Tomcat Versions</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"lower\">\r\n");
      out.write("                <div id=\"low-manage\" class=\"\">\r\n");
      out.write("                    <div class=\"curved container\">\r\n");
      out.write("                        <h3>Managing Tomcat</h3>\r\n");
      out.write("                        <p>For security, access to the <a href=\"/manager/html\">manager webapp</a> is restricted.\r\n");
      out.write("                        Users are defined in:</p>\r\n");
      out.write("                        <pre>$CATALINA_HOME/conf/tomcat-users.xml</pre>\r\n");
      out.write("                        <p>In Tomcat 9.0 access to the manager application is split between\r\n");
      out.write("                           different users. &nbsp; <a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("manager-howto.html\">Read more...</a></p>\r\n");
      out.write("                        <br />\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("RELEASE-NOTES.txt\">Release Notes</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("changelog.html\">Changelog</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("migration.html\">Migration Guide</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("security.html\">Security Notices</a></h4>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"low-docs\" class=\"\">\r\n");
      out.write("                    <div class=\"curved container\">\r\n");
      out.write("                        <h3>Documentation</h3>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Tomcat 9.0 Documentation</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("config/\">Tomcat 9.0 Configuration</a></h4>\r\n");
      out.write("                        <h4><a href=\"https://wiki.apache.org/tomcat/FrontPage\">Tomcat Wiki</a></h4>\r\n");
      out.write("                        <p>Find additional important configuration information in:</p>\r\n");
      out.write("                        <pre>$CATALINA_HOME/RUNNING.txt</pre>\r\n");
      out.write("                        <p>Developers may be interested in:</p>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"https://tomcat.apache.org/bugreport.html\">Tomcat 9.0 Bug Database</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("api/index.html\">Tomcat 9.0 JavaDocs</a></li>\r\n");
      out.write("                            <li><a href=\"https://github.com/apache/tomcat/tree/master\">Tomcat 9.0 Git Repository at GitHub</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"low-help\" class=\"\">\r\n");
      out.write("                    <div class=\"curved container\">\r\n");
      out.write("                        <h3>Getting Help</h3>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("faq/\">FAQ</a> and <a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html\">Mailing Lists</a></h4>\r\n");
      out.write("                        <p>The following mailing lists are available:</p>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li id=\"list-announce\"><strong><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#tomcat-announce\">tomcat-announce</a><br />\r\n");
      out.write("                                Important announcements, releases, security vulnerability notifications. (Low volume).</strong>\r\n");
      out.write("                            </li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#tomcat-users\">tomcat-users</a><br />\r\n");
      out.write("                                User support and discussion\r\n");
      out.write("                            </li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#taglibs-user\">taglibs-user</a><br />\r\n");
      out.write("                                User support and discussion for <a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("taglibs/\">Apache Taglibs</a>\r\n");
      out.write("                            </li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#tomcat-dev\">tomcat-dev</a><br />\r\n");
      out.write("                                Development mailing list, including commit messages\r\n");
      out.write("                            </li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"footer\" class=\"curved container\">\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Other Downloads</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("download-connectors.cgi\">Tomcat Connectors</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("download-native.cgi\">Tomcat Native</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("taglibs/\">Taglibs</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("deployer-howto.html\">Deployer</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Other Documentation</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("connectors-doc/\">Tomcat Connectors</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("connectors-doc/\">mod_jk Documentation</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("native-doc/\">Tomcat Native</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("deployer-howto.html\">Deployer</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Get Involved</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("getinvolved.html\">Overview</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("source.html\">Source Repositories</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html\">Mailing Lists</a></li>\r\n");
      out.write("                            <li><a href=\"https://wiki.apache.org/tomcat/FrontPage\">Wiki</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Miscellaneous</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("contact.html\">Contact</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("legal.html\">Legal</a></li>\r\n");
      out.write("                            <li><a href=\"https://www.apache.org/foundation/sponsorship.html\">Sponsorship</a></li>\r\n");
      out.write("                            <li><a href=\"https://www.apache.org/foundation/thanks.html\">Thanks</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Apache Software Foundation</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("whoweare.html\">Who We Are</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("heritage.html\">Heritage</a></li>\r\n");
      out.write("                            <li><a href=\"https://www.apache.org\">Apache Home</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("resources.html\">Resources</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <p class=\"copyright\">Copyright &copy;1999-");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${year}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write(" Apache Software Foundation.  All Rights Reserved</p>\r\n");
      out.write("        </div>\r\n");
      out.write("    </body>\r\n");
      out.write("\r\n");
      out.write("</html>\r\n");
  }
}

然后就会发现这特喵的不就是我们现在写的html页面，没错，但是只是相似，以前的开发，页面的每一行都是通过一个out对象来输出，也就是后端开发人员需要用这样的形式来进行开发，一个请求对应一个servlet，很多的请求，就得写很多这样的恶心代码，并且没有分层，业务，数据以及页面渲染都是写在一个servlet类里，所以为了简化我们的开发，就出现了jsp的页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>Hello World！</h1>
</body>
</html>

所以jsp页面的出现就是为了减轻开发人员的压力，究其本质一个jsp页面就是一个servlet类，不信可以看看

image.png

这就发现，项目发布之后，一个个jsp页面就被编译成了一个个xxx_jsp.java的java类，再编译成字节码文件，看看里面的东西

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/9.0.34
 * Generated at: 2020-04-22 14:45:10 UTC
 * Note: The last modified time of this file was set to
 *       the last modified time of the source file after
 *       generation to assist with modification tracking.
 */
package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {

  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;

  private static final java.util.Set<java.lang.String> _jspx_imports_packages;

  private static final java.util.Set<java.lang.String> _jspx_imports_classes;

  static {
    _jspx_imports_packages = new java.util.HashSet<>();
    _jspx_imports_packages.add("javax.servlet");
    _jspx_imports_packages.add("javax.servlet.http");
    _jspx_imports_packages.add("javax.servlet.jsp");
    _jspx_imports_classes = null;
  }

  private volatile javax.el.ExpressionFactory _el_expressionfactory;
  private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
    return _jspx_dependants;
  }

  public java.util.Set<java.lang.String> getPackageImports() {
    return _jspx_imports_packages;
  }

  public java.util.Set<java.lang.String> getClassImports() {
    return _jspx_imports_classes;
  }

  public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
    if (_el_expressionfactory == null) {
      synchronized (this) {
        if (_el_expressionfactory == null) {
          _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
        }
      }
    }
    return _el_expressionfactory;
  }

  public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
    if (_jsp_instancemanager == null) {
      synchronized (this) {
        if (_jsp_instancemanager == null) {
          _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
        }
      }
    }
    return _jsp_instancemanager;
  }

  public void _jspInit() {
  }

  public void _jspDestroy() {
  }

  public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
      throws java.io.IOException, javax.servlet.ServletException {

    if (!javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
      final java.lang.String _jspx_method = request.getMethod();
      if ("OPTIONS".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        return;
      }
      if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSP 只允许 GET、POST 或 HEAD。Jasper 还允许 OPTIONS");
        return;
      }
    }

    final javax.servlet.jsp.PageContext pageContext;
    final javax.servlet.ServletContext application;
    final javax.servlet.ServletConfig config;
    javax.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;
    javax.servlet.jsp.JspWriter _jspx_out = null;
    javax.servlet.jsp.PageContext _jspx_page_context = null;


    try {
      response.setContentType("text/html; charset=UTF-8");
      pageContext = _jspxFactory.getPageContext(this, request, response,
                null, false, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("\r\n");
      out.write("\r\n");

java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy");
request.setAttribute("year", sdf.format(new java.util.Date()));
request.setAttribute("tomcatUrl", "https://tomcat.apache.org/");
request.setAttribute("tomcatDocUrl", "/docs/");
request.setAttribute("tomcatExamplesUrl", "/examples/");

      out.write("\r\n");
      out.write("<!DOCTYPE html>\r\n");
      out.write("<html lang=\"en\">\r\n");
      out.write("    <head>\r\n");
      out.write("        <meta charset=\"UTF-8\" />\r\n");
      out.write("        <title>");
      out.print(request.getServletContext().getServerInfo() );
      out.write("</title>\r\n");
      out.write("        <link href=\"favicon.ico\" rel=\"icon\" type=\"image/x-icon\" />\r\n");
      out.write("        <link href=\"favicon.ico\" rel=\"shortcut icon\" type=\"image/x-icon\" />\r\n");
      out.write("        <link href=\"tomcat.css\" rel=\"stylesheet\" type=\"text/css\" />\r\n");
      out.write("    </head>\r\n");
      out.write("\r\n");
      out.write("    <body>\r\n");
      out.write("        <div id=\"wrapper\">\r\n");
      out.write("            <div id=\"navigation\" class=\"curved container\">\r\n");
      out.write("                <span id=\"nav-home\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Home</a></span>\r\n");
      out.write("                <span id=\"nav-hosts\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Documentation</a></span>\r\n");
      out.write("                <span id=\"nav-config\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("config/\">Configuration</a></span>\r\n");
      out.write("                <span id=\"nav-examples\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatExamplesUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Examples</a></span>\r\n");
      out.write("                <span id=\"nav-wiki\"><a href=\"https://wiki.apache.org/tomcat/FrontPage\">Wiki</a></span>\r\n");
      out.write("                <span id=\"nav-lists\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html\">Mailing Lists</a></span>\r\n");
      out.write("                <span id=\"nav-help\"><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("findhelp.html\">Find Help</a></span>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"asf-box\">\r\n");
      out.write("                <h1>");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageContext.servletContext.serverInfo}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("</h1>\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"upper\" class=\"curved container\">\r\n");
      out.write("                <div id=\"congrats\" class=\"curved container\">\r\n");
      out.write("                    <h2>If you're seeing this, you've successfully installed Tomcat. Congratulations!</h2>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"notice\">\r\n");
      out.write("                    <img src=\"tomcat.png\" alt=\"[tomcat logo]\" />\r\n");
      out.write("                    <div id=\"tasks\">\r\n");
      out.write("                        <h3>Recommended Reading:</h3>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("security-howto.html\">Security Considerations How-To</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("manager-howto.html\">Manager Application How-To</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("cluster-howto.html\">Clustering/Session Replication How-To</a></h4>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"actions\">\r\n");
      out.write("                    <div class=\"button\">\r\n");
      out.write("                        <a class=\"container shadow\" href=\"/manager/status\"><span>Server Status</span></a>\r\n");
      out.write("                    </div>\r\n");
      out.write("                    <div class=\"button\">\r\n");
      out.write("                        <a class=\"container shadow\" href=\"/manager/html\"><span>Manager App</span></a>\r\n");
      out.write("                    </div>\r\n");
      out.write("                    <div class=\"button\">\r\n");
      out.write("                        <a class=\"container shadow\" href=\"/host-manager/html\"><span>Host Manager</span></a>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"middle\" class=\"curved container\">\r\n");
      out.write("                <h3>Developer Quick Start</h3>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("setup.html\">Tomcat Setup</a></p>\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("appdev/\">First Web Application</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("realm-howto.html\">Realms &amp; AAA</a></p>\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("jndi-datasource-examples-howto.html\">JDBC DataSources</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatExamplesUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Examples</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col25\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <p><a href=\"https://wiki.apache.org/tomcat/Specifications\">Servlet Specifications</a></p>\r\n");
      out.write("                        <p><a href=\"https://wiki.apache.org/tomcat/TomcatVersions\">Tomcat Versions</a></p>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"lower\">\r\n");
      out.write("                <div id=\"low-manage\" class=\"\">\r\n");
      out.write("                    <div class=\"curved container\">\r\n");
      out.write("                        <h3>Managing Tomcat</h3>\r\n");
      out.write("                        <p>For security, access to the <a href=\"/manager/html\">manager webapp</a> is restricted.\r\n");
      out.write("                        Users are defined in:</p>\r\n");
      out.write("                        <pre>$CATALINA_HOME/conf/tomcat-users.xml</pre>\r\n");
      out.write("                        <p>In Tomcat 9.0 access to the manager application is split between\r\n");
      out.write("                           different users. &nbsp; <a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("manager-howto.html\">Read more...</a></p>\r\n");
      out.write("                        <br />\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("RELEASE-NOTES.txt\">Release Notes</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("changelog.html\">Changelog</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("migration.html\">Migration Guide</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("security.html\">Security Notices</a></h4>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"low-docs\" class=\"\">\r\n");
      out.write("                    <div class=\"curved container\">\r\n");
      out.write("                        <h3>Documentation</h3>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("\">Tomcat 9.0 Documentation</a></h4>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("config/\">Tomcat 9.0 Configuration</a></h4>\r\n");
      out.write("                        <h4><a href=\"https://wiki.apache.org/tomcat/FrontPage\">Tomcat Wiki</a></h4>\r\n");
      out.write("                        <p>Find additional important configuration information in:</p>\r\n");
      out.write("                        <pre>$CATALINA_HOME/RUNNING.txt</pre>\r\n");
      out.write("                        <p>Developers may be interested in:</p>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"https://tomcat.apache.org/bugreport.html\">Tomcat 9.0 Bug Database</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("api/index.html\">Tomcat 9.0 JavaDocs</a></li>\r\n");
      out.write("                            <li><a href=\"https://github.com/apache/tomcat/tree/master\">Tomcat 9.0 Git Repository at GitHub</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div id=\"low-help\" class=\"\">\r\n");
      out.write("                    <div class=\"curved container\">\r\n");
      out.write("                        <h3>Getting Help</h3>\r\n");
      out.write("                        <h4><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("faq/\">FAQ</a> and <a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html\">Mailing Lists</a></h4>\r\n");
      out.write("                        <p>The following mailing lists are available:</p>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li id=\"list-announce\"><strong><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#tomcat-announce\">tomcat-announce</a><br />\r\n");
      out.write("                                Important announcements, releases, security vulnerability notifications. (Low volume).</strong>\r\n");
      out.write("                            </li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#tomcat-users\">tomcat-users</a><br />\r\n");
      out.write("                                User support and discussion\r\n");
      out.write("                            </li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#taglibs-user\">taglibs-user</a><br />\r\n");
      out.write("                                User support and discussion for <a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("taglibs/\">Apache Taglibs</a>\r\n");
      out.write("                            </li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html#tomcat-dev\">tomcat-dev</a><br />\r\n");
      out.write("                                Development mailing list, including commit messages\r\n");
      out.write("                            </li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <div id=\"footer\" class=\"curved container\">\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Other Downloads</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("download-connectors.cgi\">Tomcat Connectors</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("download-native.cgi\">Tomcat Native</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("taglibs/\">Taglibs</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("deployer-howto.html\">Deployer</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Other Documentation</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("connectors-doc/\">Tomcat Connectors</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("connectors-doc/\">mod_jk Documentation</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("native-doc/\">Tomcat Native</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatDocUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("deployer-howto.html\">Deployer</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Get Involved</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("getinvolved.html\">Overview</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("source.html\">Source Repositories</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("lists.html\">Mailing Lists</a></li>\r\n");
      out.write("                            <li><a href=\"https://wiki.apache.org/tomcat/FrontPage\">Wiki</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Miscellaneous</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("contact.html\">Contact</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("legal.html\">Legal</a></li>\r\n");
      out.write("                            <li><a href=\"https://www.apache.org/foundation/sponsorship.html\">Sponsorship</a></li>\r\n");
      out.write("                            <li><a href=\"https://www.apache.org/foundation/thanks.html\">Thanks</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <div class=\"col20\">\r\n");
      out.write("                    <div class=\"container\">\r\n");
      out.write("                        <h4>Apache Software Foundation</h4>\r\n");
      out.write("                        <ul>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("whoweare.html\">Who We Are</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("heritage.html\">Heritage</a></li>\r\n");
      out.write("                            <li><a href=\"https://www.apache.org\">Apache Home</a></li>\r\n");
      out.write("                            <li><a href=\"");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${tomcatUrl}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write("resources.html\">Resources</a></li>\r\n");
      out.write("                        </ul>\r\n");
      out.write("                    </div>\r\n");
      out.write("                </div>\r\n");
      out.write("                <br class=\"separator\" />\r\n");
      out.write("            </div>\r\n");
      out.write("            <p class=\"copyright\">Copyright &copy;1999-");
      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${year}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null));
      out.write(" Apache Software Foundation.  All Rights Reserved</p>\r\n");
      out.write("        </div>\r\n");
      out.write("    </body>\r\n");
      out.write("\r\n");
      out.write("</html>\r\n");
    } catch (java.lang.Throwable t) {
      if (!(t instanceof javax.servlet.jsp.SkipPageException)){
        out = _jspx_out;
        if (out != null && out.getBufferSize() != 0)
          try {
            if (response.isCommitted()) {
              out.flush();
            } else {
              out.clearBuffer();
            }
          } catch (java.io.IOException e) {}
        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
        else throw new ServletException(t);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

是不是很神奇，可以看到其中有这样的代码

    final javax.servlet.jsp.PageContext pageContext;
    final javax.servlet.ServletContext application;
    final javax.servlet.ServletConfig config;
    javax.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;

pageContext 页面上下文对象类型 javax.servlet.jsp.PageContext 作用域 Page
application 应用程序对象类型 javax.servlet.ServletContext 作用域 Application
config 配置对象类型 javax.servlet.ServletConfig 作用域 Page
out 输出对象类型 javax.servlet.jsp.JspWriter 作用域 Page
page 页面对象类型 javax.lang.Object 作用域 Page
除了上面的5个内置对象之外，还有下面这4个内置对象
request 请求对象　类型 javax.servlet.ServletRequest 作用域 Request
response 响应对象类型 javax.servlet.SrvletResponse 作用域 Page
session 会话对象类型 javax.servlet.http.HttpSession 作用域 Session
exception 例外对象类型 javax.lang.Throwable 作用域 page
这就是传说中的jsp的9大内置对象，除了这9大内置对象，这些内置对象中用来存东西的有，pageContext、application、request、session，这四个对象可以用来存放东西，既然用来存，自然就有这些存的数据的作用吧，其中
pageContext的作用域是当前页，
application的作用域是当前应用程序，在整个web应用中生效，所以很多地方都能获得该对象，
request的作用域就是一次请求中有效，一次请求包括的转发（forward），但是不包括重定向，转发跟重定向不一样
session的作用域就是一次会话中有效，一次会话的意思就是一个从打开浏览器到关闭浏览器就是一次会话
以上就是jsp的9大内置对象和4大作用域。

如此这般，将页面从servlet类中剥离开发，使用jsp简化页面的开发，但是本质还是servlet页面，那页面剥离出去后，我们的业务逻辑，调用数据库，数据，以及页面的转发还在里面，职责不单一，所以就将这些职责一一剥离出去，架构中的一句话，没有什么是加一层解决不了的，如果一层解决不了，那就再加一层，于是就将业务逻辑代码放在了service层中，访问数据库的代码放在了dao层中，servlet的职责就变成了只是接收前端jsp页面传过来的数据，调用service层方法，service层方法再调用dao层方法，查到数据再一层层的返回，servlet层就可以将数据返回给前端jsp页面进行渲染，最后返回给用户，至此，我们的MVC模型以及三层架构行程，看图

image.png

其中有一个javabean，也有其他的叫法，比如pojo实体类，从数据库里查出来的数据都是一个个的对象对不对，并且有相同的属性，于是就写一个类跟数据库表的字段进行映射，这样返回的数据都是可以保存在对应的实体类中，这个实体类是可以在各个层中都可以被使用的。
现在，就是javaweb的一个整体结构

讲一讲cookie和session：二者都是用来保存一些数据用的

cookie的字面意思是曲奇饼，小饼干，在java中我们可以将之理解为一个信物
session：会议，会话
cookie保存的数据是在客户端的浏览器里，一些简单的数据
session保存的数据实在服务器端里，一些重要的数据，比如用户的登录信息
看代码：
cookie的

package com.hut.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;
import java.net.URLEncoder;

/**
 * 类说明
 * 如果出现编码问题，就可以使用编码以及解码
 * @Author 茶茶
 * @Create 2020-04-24 16:35 新建
 */
public class CookieDemo03 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");

        Cookie cookie = new Cookie("name", URLEncoder.encode("dh","utf-8"));
        resp.addCookie(cookie);
        PrintWriter out = resp.getWriter();
        Cookie[] cookies = req.getCookies();
        if (cookies != null){
            for (Cookie c : cookies) {
                if (c.getName().equals("name")){
                    System.out.println(c.getValue());
                    out.write("名字：" + URLDecoder.decode(c.getValue(),"utf-8"));
                }
            }
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

}

只要new一个cookie的对象，把数据存到cookie里，再将cookie存在resp这个响应对象里，就能返回给前端，cookie是保存在客户端的，看图

image.png

出现了乱码因为编码不一致

package com.hut.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * 类说明
 *
 * @Author 茶茶
 * @Create 2020-04-24 17:07 新建
 */
public class SessionDemo01 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //解决中文乱码问题
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        //获取session
        HttpSession session = req.getSession();

        //给session存东西
        session.setAttribute("name","dh");

        //获取session的id
        String sessionId = session.getId();
        System.out.println(sessionId);

        //判读session是不是新的
        if (session.isNew()){
            resp.getWriter().write("session是新创建的" + sessionId);
        }else {
            resp.getWriter().write("session已经存在" + sessionId);
        }

        //session做的事情
//        Cookie cookie = new Cookie("JSESSIONID",sessionId);
//        resp.addCookie(cookie);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

}

从req请求对象中获取一个session对象，不需要将session对象保存在resp响应对象里，因为session是保存在服务器端的，下面有一个这样的场景：就是有一个用户登录，然后判断用户名密码是否存在数据库并且都正确，都正确我们就将该用户的信息保存在一个session里，那用户跳转了一个新页面，服务器是怎么判断该用户还是刚才那个存在session里的用户呢？
原因是这样的，每有一个用户过来，我们就将该用户保存在一个session里，然后给该session一个ID，最后再将ID保存在cookie里，返回给客户端，这个ID的名字就是叫做JSESSIONID，我们可以看到

image.png

我们可以看到在同一个web项目里，只要浏览器不关闭，任何页面都会带有一个JSESSIONID，这个JSESSIONID就代表了你这个客户端，然后每次你发请求到服务器，都会带上这个JSESSIONID，注意这个JSESSIONID只在该浏览器里这一次会话，就是还未关闭浏览器有效，就好比你用同一个360浏览器登录QQ空间，只有这个浏览器未关闭，该JSESSIONID一直存在，并且只属于这一个QQ空间的web项目，浏览器同时还可以登录网易云音乐等等，所以可以这样理解，一个JSESSIONID属于的是一次会话中的同一个WEB资源中的信息，再次请求带上JSESSIONID，发给服务器，服务器根据JSESSIONID查找到只属于你的那个JSESSIONID，区别session是靠ID区别的，同名不一定是同一个session，比如有两个用户，两个客户端，登录同一个web应用，是两台电脑，然后后台session存用户的键都是userInfo，但是区分这两个用户，是不是还是得靠JSESSIONID来区分。这样既保障了登录用户的数据安全，又能区分不同的用户，使得大家不会混淆起来，如果将用户的信息存在cookie里，是不是就不安全，可以抓包抓取cookie的数据啊，账号和密码都在cookie里，很不安全，所以cookie只存一个JSESSIONID代表该用户，将用户信息存在服务器里，就相当安全啊

image.png

讲一讲javaweb里的两个对象：HttpServletRequest req和HttpServletResponse resp

这两个对象极其的重要，req对象代表了用户的一次请求，resp对象代表了一次响应

image.png

请求：请求头和请求体，里面封装了这一次请求的数据发送给服务器
响应：响应头和响应体，服务器接收到一次请求，根据这次请求，做出一次响应

讲一讲转发和重定向

转发不会改变url路径，但是重定向会改变url路径，为什么呢？

image.png

以上就是javaweb的一些知识，从最开始的servlet开发，到后来出现jsp页面，出现MVC模型以及三层架构，现在来讲讲框架。

讲一件拦截器和监听器

在使用servlet进行开发的时候，是不是就只要让servlet类继承HttpServlet，重写doGet和doPost方法就可以啦，那拦截器和监听器也是同样的道理，拦截器只需要实现一些filter接口，实现里面的方法就好了，拦截器的作用就是拦截所有进来的请求，做一些相应的操作，也会拦截所有出去的响应，这就可以很好的帮我们解决字符编码的问题呀
拦截器代码

package com.hut.filter;

import javax.servlet.*;
import java.io.IOException;

/**
 * 类说明
 * 过滤器
 * @Author 茶茶
 * @Create 2020-04-24 21:53 新建
 */
public class CharacterEncodingFilter implements Filter {

    //初始化：web服务器启动，就已经初始化了，随时等待过滤对象出现
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化了");
    }

    //Chain : 链
    /*
    1.过滤中的所有代码，在过滤特定请求的时候都会执行
    2.必须要让过滤器继续进行
        filterChain.doFilter(servletRequest,servletResponse);
     */
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=utf-8");

        System.out.println("CharacterEncodingFilter执行前");
        filterChain.doFilter(servletRequest,servletResponse);//让我们的程序继续走，如果不写，请求就被拦截了
        System.out.println("CharacterEncodingFilter执行后");

    }

    //销毁
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁了");
    }

}

监听器，是不是就是监听一个个对象的动作，从对象的出生，到对象的死亡，可以一直监听着，并对于对象的每一个动作进行一些事件，比如HttpSession对象的产生，就可以监听网站在线人数+1等等。
监听器代码

package com.hut.listen;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * 类说明
 * 在线人数监听
 * @Author 茶茶
 * @Create 2020-04-24 22:53 新建
 */
public class OnlineCountListen implements HttpSessionListener {

    //创建session监听
    //一旦一个session被创建了就执行该方法
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();
        System.out.println(httpSessionEvent.getSession().getId());
        Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount");
        if (onlineCount==null){
            onlineCount = new Integer(1);
        }else {
            int count = onlineCount.intValue();
            onlineCount = ++count;//人数+1
        }
        servletContext.setAttribute("OnlineCount",onlineCount);
    }

    //销毁session监听
    //一旦一个session被销毁了就执行该方法
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();
        Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount");
        if (onlineCount==null){
            onlineCount = new Integer(0);
        }else {
            int count = onlineCount.intValue();
            onlineCount = --count;//人数+1
        }
        servletContext.setAttribute("OnlineCount",onlineCount);
    }

    /*
    session的销毁
    1、手动销毁   httpSessionEvent.getSession().invalidate();
    2、在web.xml中配置session的过期时间
     */

}

框架

框架的出现，为什么会出现框架，用来干嘛的？
三层架构是控制器层，业务层和数据持久层，也就是controller层，service层和dao层
首先controller层，以前是一个个的servlet类，每写一个servlet类就要马上去web.xml里注册一个servlet，那要是大项目，成百上千个servlet类就要注册成百上千个的servlet，那就太太太麻烦了，并且不容易维护，于是出现springmvc框架，就是来帮我们大大简化控制层的开发的，看图

image.png

springmvc的具体配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!--开启注解扫，只扫描@Controller注解的类-->
    <context:component-scan base-package="com.hut.controller">
        <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"></context:include-filter>
    </context:component-scan>

    <!--配置视图解析器-->
    <bean id="internalResourceViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/pages/"></property>
        <property name="suffix" value=".jsp"></property>
    </bean>

    <!--过滤静态资源-->
    <mvc:resources mapping="/css/**" location="/statics/css"></mvc:resources>
    <mvc:resources mapping="/images/**" location="/statics/images"></mvc:resources>
    <mvc:resources mapping="/js/**" location="/statics/js"></mvc:resources>

    <!--开启SpringMVC注解的支持-->
    <mvc:annotation-driven></mvc:annotation-driven>

</beans>

springmvc只管我们的controller层，所以springmvc.xml配置文件只扫描controller包下@Controller注解，配置视图解析器的作用，控制器层里的方法只返回字符串，springmvc框架拿到返回的值后，拼接完整的路径/WEB-INF/pages/hello.jsp页面，所以这样子方法就只返回具体页面名字，就不用加具体的路径了，其次，web.xml是不是把所有的请求路径，包括资源路径都给拦截了，但是资源是不需要拦截的对不对，直接去找项目里的资源，所以资源路径要放行，因此过滤静态资源也是必须的，最后开启一下注解支持，使得能够使用注解开发，方便许多。
然后控制器层对应的流行框架是springmvc框架，那service层和dao层是不是也要分别对应一层框架，service层就对应spring框架，dao层对应mybatis框架，这就是传统企业开发的SSM框架

spring框架的配置文件和mybatis框架的配置文件，为了方便，一般将mybatis框架放进spring的配置文件里

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans   
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">

    <!--在web.xml里加载这个spring的配置文件，服务器已启动便创建spring容器，然后将Service层和dao层的bean对象存储在容器中-->
    <!--Service层有自己的实现类，加载进spring容器-->
    <!--dao层没有让自己编写实现类，dao层的接口由MyBatis框架来帮我们实现，所以在下面配置MyBatis，在创建spring容器时，也加载MyBatis的配置文件，并将dao层的bean对象存进spring容器中-->

    <!--配置扫描包，管理service层和mapper层的bean对象-->
    <context:component-scan base-package="com.hut">
        <!--不扫描用注解@Controller的类-->
        <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"></context:exclude-filter>
    </context:component-scan>

    <!--spring整个mybatis框架，加载mybatis的核心配置文件-->
    <!--配置连接池-->
    <!--导入c3p0依赖-->
    <!--com.mchange.v2.c3p0.ComboPooledDataSource在c3p0jar包下-->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/ssm"></property>
        <property name="user" value="root"></property>
        <property name="password" value="123456"></property>
    </bean>

    <!--配置SqlSessionFactory工厂对象-->
    <!--导入mybatis-spring依赖-->
    <!--导入spring-jdbc依赖-->
    <!--org.mybatis.spring.SqlSessionFactoryBean在mybatis-spring包下-->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
    </bean>

    <!--配置接口所在的包-->
    <!--导入mybatis-spring依赖-->
    <!--org.mybatis.spring.mapper.MapperScannerConfigurer在mybatis-spring包下-->
    <bean id="mapperScanner" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.hut.mapper"></property>
    </bean>

    <!--声明式事务管理-->
    <!--配置事务管理器-->
    <!--org.springframework.jdbc.datasource.DataSourceTransactionManager在spring-jdbc包下-->
    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"></property>
    </bean>

    <!--配置事务通知-->
    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <tx:method name="*" isolation="DEFAULT"/>
        </tx:attributes>
    </tx:advice>

    <!--配置AOP的增强-->
    <!--导入-->
    <aop:config>
        <aop:advisor advice-ref="txAdvice" pointcut="execution(public * com.hut.service.impl.*ServiceImpl.*(..))"></aop:advisor>
    </aop:config>

</beans>

首先同样的，spring配置文件，由于整合了mybatis框架的配置文件，所以spring的配置文件要扫描除了@Controller的注解，也就是只扫描@Service和@Respository这两个注解配置的类，然后还要配置一下AOP的增强，这就是Spring最重要的两点，IOC和AOP，然后配置一下MyBatis的配置，首先数据源是肯定要，因为你要连接数据库嘛，然后需要将SqlSessionFacrotyBean的对象放进spring容器里，最后配置一下，对应的dao层所在的位置，存放进MapperScannerConfigurer对象里，因为Mybatis不需要我们写JDBC的那些连接代码，只让我们专注于sql语句的编写和返回的数据集映射，所以dao层就是一个接口层，具体的实现由mybatis框架帮我们实现，这样大大的简化了我们的代码，最后如果有事务的要求，配置一些声明式事务管理，事务管理也需要数据源，还要配置一下事务的管理者，前面是开启事务管理，后面是一个事务管理者管理所有的事务，至此spring，springmvc，mybatis的配置文件都写好了，但是写好了归写好了，是不是没有应用上啊，启动一个项目，鬼知道要帮你加载这三个配置文件啊，所以像以前注册servlet一样，要注册到web.xml里面啊，因为启动项目，会默认读取web.xml里面的东西，所以只要将这些配置文件塞进web.xml里面，就可以啦

web.xml的配置

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>

  <!--配置spring的监听器，默认只加载WEB-INF目录下的applicationContext.xml配置文件-->
  <!--解决方案1：将applicationContext.xml配置文件复制一份放在WEN-INF目录下-->
  <!--解决方案2：指定加载的类路径-->
  <!--org.springframework.web.context.ContextLoaderListener在spring-web包下-->
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <!--用方案2：设置配置文件的路径-->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>

  <!--配置前端控制器-->
  <!--org.springframework.web.servlet.DispatcherServlet在spring-webmvc包下-->
  <servlet>
    <servlet-name>dispatcherServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <!--加载springmvc.xml配置文件-->
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:springmvc.xml</param-value>
    </init-param>
    <!--启动服务器，创建该servlet-->
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>dispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

  <!--解决中文乱码的过滤器-->
  <!--org.springframework.web.filter.CharacterEncodingFilter在spring-web包下-->
  <filter>
    <filter-name>haracterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <!--设置编码集-->
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>haracterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

先配置一个监听器，当加载上下文的时候，加载上我们的spring的配置文件--->applicationContext.xml
然后配置一个Servlet，前端控制器，就不需要注册很多的servlet来控制所有的请求，加载这个前端控制器的时候，加个初始化参数，把springmvc.xml配置文件给加载了，这样我们的框架就被应用上去了，最后注册一个拦截器，帮我们处理乱码的问题，使用同一的编码格式UTF-8，所有的准备工作就做好了，我们就只要专注于web应用的业务开发就好了呀。

又来啦又来啦，SpringBoot它来啦

上面SSM框架的开发配置文件是不是超级繁琐，并且随着需求，配置文件里的东西越来越多，变成了配置地狱，并且出错了还不容器找到原因，于是就出现了SpringBoot，它还有个名字叫做SpringBoot全家桶，所以SpringBoot其实是帮我们开发人员减少配置文件用的啊，暂且先这么看待它，它帮我们把所有框架的配置全都配置好了，我们只管开发项目就好了，基本上就不用去管配置文件那些玩意了，因为那些配置让人头疼，而springboot直接帮我们把配置文件搞定了，爽不爽，上来就开始写业务，经理再也不用担心我配置文件出错啦。其实springboot不仅帮我们简化了配置，还内嵌了tomcat容器，使用SSM框架的时候，项目的发布还需要放在tomcat容器里，但是springboot连tomcat都帮我们内嵌了，只需要指定一下tomcat的端口号就行啦，所以springboot主要是用于微服务的开发。

最后编辑于：2020.04.29 13:02:10

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javaweb发展历程

简介

讲一讲cookie和session：二者都是用来保存一些数据用的

讲一讲javaweb里的两个对象：HttpServletRequest req和HttpServletResponse resp

讲一讲转发和重定向

讲一件拦截器和监听器

框架

springmvc的具体配置

spring框架的配置文件和mybatis框架的配置文件，为了方便，一般将mybatis框架放进spring的配置文件里

web.xml的配置

又来啦又来啦，SpringBoot它来啦

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