过滤器、监听器常见应用

监听器：GUI编程中经常使用

import javafx.scene.layout.Pane;

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class TestPanel {
    public static void main(String[] args) {
        frame frame = new frame("春节快乐");//新建一个窗体
        Panel panel = new Panel(null);//一个面板
        frame.setLayout(null);//设置窗体的布局
        frame.setBounds(300,300,500,500);
        frame.setBackground(new Color(0,0,255));//设置背景颜色
        panel.setBounds(50,50,300,300);
        panel.setBackground(new Color(0,255,0));//设置背景颜色
        frame.add(panel);
        frame.setVisible(true);
        //监听事件，关闭事件
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowOpened(WindowEvent e) {
                System.out.println("打开");
            }

            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("关闭ing");
                System.exit(0);
            }

            @Override
            public void windowClosed(WindowEvent e) {
                System.out.println("关闭");
            }

            @Override
            public void windowIconified(WindowEvent e) {
                super.windowIconified(e);
            }

            @Override
            public void windowDeiconified(WindowEvent e) {
                super.windowDeiconified(e);
            }

            @Override
            public void windowActivated(WindowEvent e) {
                System.out.println("激活");
            }

            @Override
            public void windowDeactivated(WindowEvent e) {
                System.out.println("未激活");
            }
        });
    }
}

过滤器

场景：

用户登录之后才能进入主页！用户注销就不能进入主页

用户登录之后，向session中放入用户的数据

package com.yang.servlet;

import com.yang.util.Constant;

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

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取前端请求的参数
        String username = req.getParameter("username");
        if (username.equals("admin")){ //登录成功
            req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());
            resp.sendRedirect("/sys/success.jsp");
        }else{//登录失败
            resp.sendRedirect("/error.jsp");
        }
    }

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

进入主页之后要判断用户是否已经登陆

package com.yang.filter;


import com.yang.util.Constant;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SysFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response= (HttpServletResponse) resp;
        if (request.getSession().getAttribute(Constant.USER_SESSION)==null){
            response.sendRedirect("/error.jsp");
        }
        filterChain.doFilter(request,response);
    }

    public void destroy() {

    }
}