00.通过demo进行学习（编写登录验证页面进行学习filter）

1.编写一级过滤器，实现编码的统一

package demo.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpFilter;

//@WebFilter("/*")     //后面统一使用xml进行配置
public class Filter1 extends HttpFilter implements Filter {


    public void init(FilterConfig fConfig) throws ServletException {
        System.out.println("初始化请求第一个过滤器！");
    }
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("一级过滤器启动！");
        
        //编码统一，处理乱码！
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        
        chain.doFilter(request, response);
        System.out.println("一级过滤器通过！");
    }
    
    public void destroy() {
        System.out.println("一级过滤器destory");
    }
    
    

}

2.编写二级过滤器实现访问当前文件夹下的Servlet，如果用户已经登录则显示“登录成功”，否则再次跳转到登录页面，并显示“请登录”

package demo.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

/**
 * 登录验证的过滤器
 */
//@WebFilter("/request/*")
public class Filter2 implements Filter {


    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
         System.out.println("二级过滤器启动！");
        
        //0.强制转换
          HttpServletRequest request = (HttpServletRequest) req;
        //HttpServletResponse response = (HttpServletResponse) req;

        //1.获取资源请求路径
        String uri = request.getRequestURI();
        //2.判断是否包含登录相关资源路径,要注意排除掉其他资源    
        if( uri.contains(" uri.contains(\"/login2.jsp\") || /LoginServlet") || uri.contains("/css/") || uri.contains("/js/") || uri.contains("/fonts/") || uri.contains("/checkCodeServlet")  ){
            //包含，用户就是想登录。放行
            chain.doFilter(req, resp);
            System.out.println("二级过滤器通过！");
        }else{
            //不包含，需要验证用户是否登录
            //3.从获取session中获取user
            Object user = request.getSession().getAttribute("uname");
            if(user != null){
                request.setAttribute("login_message","登录成功！");
                 System.out.println("二级过滤器通过，并登录成功！");
                //登录了。放行
                chain.doFilter(req, resp);
               
            }else{
                //没有登录。跳转登录页面

                request.setAttribute("login_msg","请登录！");
                request.getRequestDispatcher("/login2.jsp").forward(request,resp);
            }
        }



    }

    public void init(FilterConfig config) throws ServletException {

    }

    public void destroy() {
    }

}

2-1、登录验证的servlet

package com.filter.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        

        String username = request.getParameter("username");
        String pwd = request.getParameter("pwd");
        
        //获取Session
        HttpSession session = request.getSession();
        
        //验证用户名和密码是否有效
        
        //将用户名放入session    并且设置名称为uname(在过滤器中获取时，直接获取uname)
        session.setAttribute("uname",username);
        //设定session的有效期
        session.setMaxInactiveInterval(900);
        
        //将获取的用户名和密码打印在页面上
        response.getWriter().print("用户名："+username);
        response.getWriter().print("<br/>");
        response.getWriter().print("密码："+pwd);
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

2-2、登录的表单

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
<form action="LoginServlet" method="post"> 
      用户名：<input type="text" name="username"/><br/>
      密码：<input type="password"  name="pwd"/><br/>
      <input type="submit" value="提交"/>
      
      
</form>


</body>
</html>

3. 在xml文件配置中实现过滤器链

<!-- filter1过滤器配置文件 -->
     <filter>
        <filter-name>Filter1</filter-name>
        <!-- 注意自己项目的路径 -->
        <filter-class>demo.filter.Filter1</filter-class>    
    </filter>
    <filter-mapping>
        <filter-name>Filter1</filter-name>
        <url-pattern>/*</url-pattern>      
    </filter-mapping>
    
    <!-- filter2过滤器配置文件 -->
    <filter>
        <filter-name>Filter2</filter-name>
            <!-- 注意自己项目的路径 -->
        <filter-class>demo.filter.Filter2</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>Filter2</filter-name>
        <url-pattern>/*</url-pattern>       
    </filter-mapping>