2021.3.16 JavaEE3 Filter 笔记

《学习内容》：

//========学习内容=========
Filter基本使用
Filter管理机制
Filter链的执行
责任链模式

《知识点—笔记》
//=========================

《代码内容》：
TestFilder

package filter;
import javax.servlet.*;
import javax.servlet.http.HttpFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
public class TestFilter extends HttpFilter {
    protected void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpSession session = request.getSession();
        String username = (String)session.getAttribute("username");
        String requestURI = request.getRequestURI();
        System.out.println("URI"+"==="+requestURI);
        if (requestURI.contains("index") || requestURI.contains("login")){
            chain.doFilter(request,response);
        }else {
            if (username != null){
                request.getRequestDispatcher("welcome.jsp").forward(request,response);
            }else {
                request.getRequestDispatcher("index.jsp").forward(request, response);
            }
        }
    }
}

LoginController

package controller;
import service.LoginService;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
public class LoginController extends HttpServlet {
    private static LoginService service = new LoginService();
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("控制层执行了");
        request.setCharacterEncoding("UTF-8");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println(username+"--"+password);
        String loginResult = service.login(username,password);
        HttpSession session = request.getSession();
        session.setAttribute("loginResult",loginResult);
        System.out.println(loginResult);
        if ("登录成功".equals(loginResult)){
            session.setAttribute("username",username);
            session.setMaxInactiveInterval(10);
            request.getRequestDispatcher("welcome.jsp").forward(request,response);
        }else {
            request.getRequestDispatcher("idnex.jsp").forward(request,response);
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doPost(request,response);
    }
}

web.xml

<?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">
    <filter>
        <filter-name>request</filter-name>
        <filter-class>filter.TestFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>request</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <servlet>
        <servlet-name>login</servlet-name>
        <servlet-class>controller.LoginController</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>login</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
</web-app>

学习总结：
学懂的：
通过Filter过滤器**去过滤在servlet执行之前的操作，那么如果有多个Filter对象，他是怎么执行的呢？——经过测试，他是按照配置文件依次执行
但是经过模拟Filter底层发现，原**来他是用了ArrayList集合，他是有序可重复的，所以他是依次执行的。
有问题的地方：
学习完责任链设计模式后 感觉暂时没有可以想到的应用场景.