27.servlet

第一个servlet

image.png
//FirstServlet.java
package com.imooc.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FirstServlet extends HttpServlet{

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //接收请求发来的参数
        String name = request.getParameter("name");
        String html = "<h1 style='color:red'>hi," + name +"!</h1><hr/>";
        System.out.println("返回给浏览器的响应数据为：" + html);
        PrintWriter out = response.getWriter();
        out.println(html);//将html发送回浏览器
    }
    
}


//web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>FirstServlet</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <!-- 声明Servlet -->
  <servlet>
    <!-- servlet的别名 -->
    <servlet-name>first</servlet-name>
    <servlet-class>com.imooc.servlet.FirstServlet</servlet-class>
  </servlet>
  
  <!-- 将Servlet与URL绑定 -->
  <servlet-mapping>
    <servlet-name>first</servlet-name>
    <url-pattern>/hi</url-pattern>
  </servlet-mapping>
</web-app>

在地址栏输入 http://localhost:8080/servlet 即可

image.png

通过xml地址中的/hi 匹配到servlet-name:first,然后找到对应的类FirstServlet去对网址进行响应

2 Java web 工程结构

image.png

image.png

如图：在项目中的文件结构，其实也会对应发布到tomcat中，如D:\software\java\apache-tomcat-8.5.50\webapps\ServletProj

2.1 首页index.html

index.html的内容会在输入http://localhost:8080/ServletProj/后显示，即首页
`

3 Servlet开发步骤


4通过表单发送数据给tomact,完成数据request和response

请求参数
请求参数是指浏览器通过请求向Tomcat请求的数据
请求参数通常是用户输入的数据，待servlet进行处理
参数名=值1&参数名2=值2&参数名n=
http://localhost:8080/ServletProj/ComputerServlet?name=122&mobile=3333&sex=male&spec=English
<form action="">action是表单提交后发送的地址是什么
request.getParamenter() 接收单个参数
request.getParamenterValues 接收多个同名参数

表单位置

//Student.html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <h1>学生信息登记表</h1>
    <form action="http://localhost:8080/ServletProj/ComputerServlet">
        姓名：<input type="text" name="name"> <br>
        电话：<input type="text" name="mobile"> <br>
        性别：
        <select name="sex" id="">
            <option value="male" >男</option>
            <option value="female">女</option>
        </select> <br>
        <input type="checkbox" name="spec" value="English">英语
        <input type="checkbox" name="spec" value="Program">编程
        <input type="checkbox" name="spec" value="Speech">演讲
        <input type="checkbox" name="spec" value="swimming">游泳<br>
        <input type="submit" value="提交">
    </form>
</body>
</html>

//cal.java
package com.imooc.test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Cal extends HttpServlet{

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String mobile = request.getParameter("mobile");
        String sex = request.getParameter("sex");
        String[] specs = request.getParameterValues("spec");
        PrintWriter out = response.getWriter();
        out.println("<h1>"+name+"</h1>");
        out.println("<h1>"+mobile+"</h1>");
        out.println("<h1>"+sex+"</h1>");
        for(String spec:specs) {
            out.println("<h1>"+spec+"</h1>");
        }
        
    }
    
}

//web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>ServletProj</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>goods</servlet-name>
    <servlet-class>com.imooc.test.WebTest</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>goods</servlet-name>
    <url-pattern>/ShopServlet</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>cal</servlet-name>
    <servlet-class>com.imooc.test.Cal</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>cal</servlet-name>
    <url-pattern>/ComputerServlet</url-pattern>
  </servlet-mapping>
</web-app>

在地址栏输入http://localhost:8080/ServletProj/Student.html 即可

5."get" "post"

5.1

可以在表单上指定提交方式，默认为get


image.png

请求参数不会再出现在地址栏，而是以Form Data的形式


image.png

service方法是对GET和POST均可以
request.getMethod();可以获取当前的方式为POST GET


image.png

5.2 不同的请求方式对应不同的方法

//GetPostTest.java
package com.imooc.test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class GetPostTest extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        PrintWriter out = response.getWriter();
        out.print("<h1> menthod:GET name:"+name+"</h1>");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        PrintWriter out = response.getWriter();
        out.print("<h1> menthod:POST name:"+name+"</h1>");
    }
}

//Student2.java
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <h1>学生信息登记表</h1>
    <form action="http://localhost:8080/ServletProj/request_method" method="post">
        姓名：<input type="text" name="name"> <br>
        电话：<input type="text" name="mobile"> <br>
        性别：
        <select name="sex" id="">
            <option value="male" >男</option>
            <option value="female">女</option>
        </select> <br>
        <input type="checkbox" name="spec" value="English">英语
        <input type="checkbox" name="spec" value="Program">编程
        <input type="checkbox" name="spec" value="Speech">演讲
        <input type="checkbox" name="spec" value="swimming">游泳<br>
        <input type="submit" value="提交">
    </form>
</body>
</html>

//web.xml 增加内容
  <servlet>
    <servlet-name>method</servlet-name>
    <servlet-class>com.imooc.test.GetPostTest</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>method</servlet-name>
    <url-pattern>/request_method</url-pattern>
  </servlet-mapping>

地址栏输入：http://localhost:8080/ServletProj/Student2.html

6 servlet周期

servlet生命周期：
装载-web.xml（Tomcat解析XML）此时Tomcat只是解析，并未对其做什么操作
创建-构造函数 第一次访问的时候，创建servlet对象执行构造函数
初始化-init() 调用init（）方法初始化
提供服务-service( ) /doGet( )/doPost( )
销毁-destroy() tomcat关闭或重启的时候执行destory( )

package com.imooc.test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class GetPostTest extends HttpServlet{
    public  GetPostTest() {
        System.out.println("正在创建GetPostTest对象");
    }
    @Override
    public void init() throws ServletException {
        System.out.println("正在初始化GetPostTest对象");
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        PrintWriter out = response.getWriter();
        out.print("<h1> menthod:GET name:"+name+"</h1>");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        PrintWriter out = response.getWriter();
        out.print("<h1> menthod:POST name:"+name+"</h1>");
    }
    
    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("正在销毁GetPostTest对象"); 
        
    }
}

7.注解简化配置

@WebServlet("/anno")
public class Anotation extends HttpServlet{
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        resp.getWriter().print("Anotation");
    }
}

通过@WebServlet("/anno")无需配置web.xml

8.启动时加载

根据前面servelt生命周期的可知，init方法是在建立的时候初始化servlet时调用的。现在需要在加载web.xml时，就调用

8.1启动时加载数据库

public class LoadDatabase extends HttpServlet{
    @Override
    public void init() throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("正在加载数据库");
    }
}

8.2 启动时导入数据

public class ImportData extends HttpServlet{
    @Override
    public void init() throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("正在导入数据");
    }
}

8.3 web.xml

<servlet>
    <servlet-name>loadDatabase</servlet-name>
    <servlet-class>com.imooc.test.LoadDatabase</servlet-class>
    <load-on-startup>0</load-on-startup>
  </servlet>
  <servlet>
    <servlet-name>importData</servlet-name>
    <servlet-class>com.imooc.test.ImportData</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>

注意：

image.png

可以在web.xml中配置，也可以使用注解，就不用配置xml了。

8.4 启动时分析数据

@WebServlet(urlPatterns="/unused",loadOnStartup=2)
public class AnalyData extends HttpServlet{
    @Override
    public void init() throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("正在分析数据");
    }
}

需要注意的是，通过配置web.xml时，因为这个过程没有服务，因此无需写
<servlet-mapping>~</servlet-mapping>的映射地址
但是在使用注释的时候，一定要写上映射地址，可以理解为一个bug，虽然写了映射地址也用不到，但是不写，就无法生效
@WebServlet(urlPatterns="/unused",loadOnStartup=2)

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