最简单的Servlet继承HttpServlet查询数据库登录验证

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<%--
Created by IntelliJ IDEA.
User: yunqing
Date: 2017-12-06
Time: 9:11
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>login</title>
</head>
<body>
<form action="/LoginFromMysql" method="post">
用户名：<input type="text" name="username">
密码：<input type="password" name="password">
<input type="submit" value="submit">
</form> </body>
</html>

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_3_1.xsd"
version="3.1">

<servlet>
<servlet-name>fromMysql</servlet-name>
<servlet-class>com.yunqing.servlet.LoginFromMysql</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>fromMysql</servlet-name>
<url-pattern>/LoginFromMysql</url-pattern>
</servlet-mapping>
</web-app>

LoginFromMysql.java

package com.yunqing.servlet;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.*;public class LoginFromMysql extends HttpServlet { public static final String url = "jdbc:mysql://localhost:3306/mybatis";
public static final String name = "root";
public static final String pass = "5678"; Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null; @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取前端表单中的数据
String username = req.getParameter("username");
String password = req.getParameter("password"); try {
//需要添加mysql-connector-java-xxx-bin.jar(在idea中需要把jar包放到TomCAT的lib目录中)
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url,name,pass);
String sql = "SELECT COUNT(id) FROM t_user t WHERE t.name = ? AND t.gender = ?";
ps = conn.prepareStatement(sql);
ps.setString(1,username);
ps.setString(2,password); rs = ps.executeQuery();
while (rs.next()) {
int count = rs.getInt(1);
if (count > 0) {
resp.getWriter().print("Success=" + username);
} else {
resp.getWriter().print("Error=" + username + "BCZ");
}
} } catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (rs != null) {
rs.close();
}
if (ps != null) {
ps.close();
}
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
} }
}
}