Tips ： Finally, there is a real column including all class contents

Filter filter

Filters can also be called preprocessors , He's executing a page （servlet Or web page ） A program executed before , Often used to verify cookie Or filter through （ A way to crack web pages ）

Fitter You can specify which page or pages to execute ：
For example, if I want to execute on all pages, I use /*（* For wildcard ）
If you just want to servlet-mapping by /abc Page execution of , Only need to filter-mapping Change it to /abc that will do
If you just want to abc.jsp Page execution of , Only need to filter-mapping Change it to /abc.jsp that will do

Write fiter Interface is required when implements Filter
Also on doFilter Rewrite
@Override
public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException

wildcard

It can be seen above that the settings are mapping You can use wildcards when you use , This involves matching priorities
It is divided into three parts ：
First, match the exact match
Match again /* wildcard
Then match the suffix wildcard

for instance ：
I have a 5 individual servlet Of mapping Respectively /abc.k 、/abc、/* 、/abc/* 、/*.k
I'm now typing in the browser ： project /abc
First match /abc, Yes , Show the second
I'm now typing in the browser ： project /ab
First match /ab, No,
Next match /*, There are two ：/*、/abc/* , Will choose the long one , So the fourth
without /*, Will match /*.k

Cookie Brief introduction

1. The server script sends a series of cookie Go to browser . Such as name , Age ,ID Number and so on .
2. The browser stores this information on the local machine , For a rainy day .
3. The next time the browser sends any request to the server , It will put these cookie The message is sent to the server , Then the server uses that information to identify users or do something else .

In fact, there is nothing like what has been learned ：session, I thought a session Just a user , This is not entirely accurate , For example, I log in to a website , I quit my current login account again , Log in to another account , One session It corresponds to two users , And if only session If you exit the account, when we realize automatic login , Only by setting session The survival time to complete .cookie Simplify these operations ：
Set up cookie Methods ：

Cookie cookie = new Cookie("user", user+"-"+password);
cookie.setPath(req.getContextPath());/ The valid range is my web page 
cookie.setMaxAge(60*60*1);/ Valid for one hour 
resp.addCookie(cookie);

Set up cookie It will be sent as follows ：
Copy the picture of the rookie , The parameter does not correspond to

Actual items

utilize Filter filter 、 Wildcards and Cookie Handle , Automatic login
Of the login page servlet：

package com.ljq;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.activation.DataSource;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.RequestDispatcher;
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 javax.servlet.http.HttpSession;

import com.mysql.cj.exceptions.DataReadException;
import com.sun.org.apache.bcel.internal.generic.Select;
import com.sun.xml.internal.bind.CycleRecoverable.Context;

import sun.awt.windows.WPrinterJob;

public class loginservlet extends HttpServlet {
    
	@Override
	public void init() throws ServletException {
    
		// TODO Auto-generated method stub
		super.init();
	}
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
		// TODO Auto-generated method stub
		HttpSession session = req.getSession();
		req.setCharacterEncoding("utf-8");
		resp.setContentType("text/html;charset=utf-8");
		PrintWriter pWriter = resp.getWriter();
		String user = req.getParameter("user");
		String password = req.getParameter("password");
		String string = null;
		if (user == null || password == null || user.length() == 0 || password.length() == 0) {
    
			session.setAttribute("failmess", ", Input empty ");
			string = "loginfail.jsp";
		}
		String dataBase = "updatabase";
		String mysqluser = "root";
		String mysqlpassword = "123";
		String table = "up";
		String ruser[][] = null;
		if (string == null)
		try {
    
			Connection connection = DriverManager.getConnection("jdbc:mysql://192.168.101.121:3306/"+dataBase+"?"+"userSSL=false&serverTimezone=CST&characterEncoding=utf-8",mysqluser,mysqlpassword);
			Statement sql = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY,ResultSet.CONCUR_READ_ONLY);
			ResultSet rs = (ResultSet)sql.executeQuery("Select * from "+table);
			rs.last();
			int n = rs.getRow();
			rs.beforeFirst();
			ruser = new String[n][2];
			int i = 0;
			while(rs.next()) {
    
				ruser[i][0] = rs.getString(1);
				ruser[i][1] = rs.getString(2);
				i++;
			}
			sql.close();
			if (ruser == null || ruser.length == 0)
			{
    
				session.setAttribute("failmess", ", Database has no data or read error ");
				string = "loginfail.jsp";
			}
			if ((i = login(ruser, user, password)) != -1) {
    
				Userbean Userbean = new Userbean();
				Userbean.setUser(user);
				Userbean.setPassword(password);
				Userbean.setImage(user+".png");
				session.setAttribute("Userbean", Userbean);
				string = "loginsuccess.jsp";
				String autoLogin = req.getParameter("autologin");
				if (autoLogin.equals("1 Hours of automatic login ")) {
    
					Cookie cookie = new Cookie("user", user+"-"+password);
					cookie.setPath(req.getContextPath());
					cookie.setMaxAge(60*60*1);
					resp.addCookie(cookie);
				}
				else{
    
					Cookie cookie = new Cookie("user", user+"-"+password);
					cookie.setPath(req.getContextPath());
					cookie.setMaxAge(60*5);
					resp.addCookie(cookie);
				}
			}
			else {
    
				session.setAttribute("failmess", ", Wrong password ");
				string = "loginfail.jsp";
			}
		} catch (SQLException e) {
    
			// TODO Auto-generated catch block
			e.printStackTrace();
			session.setAttribute("failmess", ", Database connection failed ");
			string = "loginfail.jsp";
		}
		resp.sendRedirect(string);
// try {
    
// Context context = (Context) new InitialContext();
// Context contextNeeded = (Context)((InitialContext) context).lookup("java:comp/env");
// DataSource ds = (DataSource)((InitialContext) contextNeeded).lookup("up");
// System.out.println(ds);
// } catch (NamingException e) {
    
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
		
		
	}
	public int login(String mysqlup[][], String user, String password) {
    
		for (int i = 0; i < mysqlup.length; i++) {
    
			if (mysqlup[i][0].equals(user) && mysqlup[i][1].equals(password))
			{
    
				return i;
			}
		}
		return -1;
	}
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
		// TODO Auto-generated method stub
		doPost(req, resp);
	}
}

It has been set according to the user's requirements cookie

Fiter Agency buying in ：

package com.ljq;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.xml.ws.Dispatch;

import com.sun.xml.internal.ws.client.dispatch.DataSourceDispatch;

public class AutoLoginFilter implements Filter{
    
	@Override
	public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
			throws IOException, ServletException {
    
		// TODO Auto-generated method stub
		req.setCharacterEncoding("utf-8");
		HttpServletRequest request2 = (HttpServletRequest)req;
		HttpSession session = request2.getSession();
		Cookie[] cookies = request2.getCookies();
		String userp = null;
		for (int i = 0; cookies != null && i < cookies.length; i++) {
    
			if ("user".equals(cookies[i].getName())) {
    
				userp = cookies[i].getValue();
				break;
			}
		}
		Userbean Userbean = (Userbean)session.getAttribute("Userbean");
		if (userp != null && Userbean != null) {
    
			String[] userpp = userp.split("-");
			String user = userpp[0];
			String password = userpp[1];
			
			if (!user.equals(Userbean.getUser()) || !password.equals(Userbean.getPassword()))
			{
    
				Userbean.setUser(null);
				Userbean.setPassword(null);
			}
		}
		else if (Userbean!=null){
    
				Userbean.setUser(null);
				Userbean.setPassword(null);
				Userbean.setImage(null);
		}
		chain.doFilter(request2, resp);
	}
	
	public int login(String mysqlup[][], String user, String password) {
    
		for (int i = 0; i < mysqlup.length; i++) {
    
			if (mysqlup[i][0].equals(user) && mysqlup[i][1].equals(password))
			{
    
				return i;
			}
		}
		return -1;
	}
	
}

Exited servlet：
Because... Cannot be deleted cookie, We can directly set his validity period to 0, Let him expire

package com.ljq;

import java.io.IOException;

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

public class Logout extends HttpServlet{
    

	protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
			throws ServletException, IOException {
    
		
		//  remove session
		req.getSession().removeAttribute("Userbean");
		//  establish cookie
		Cookie cookie = new Cookie("user", "msg");
		cookie.setPath(req.getContextPath());

		//  take cookie Set as expired 
		cookie.setMaxAge(0);
		resp.addCookie(cookie);
		
		//  Navigation , Redirect 
		resp.sendRedirect(req.getContextPath()+"/index.jsp");
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
    
		doGet(request, response);
	}

}

Exhibition ：