Servlet案例1：用户登录

数据库准备：

CREATE DATABASE web;
USE web;
CREATE TABLE users(
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(64),
    PASSWORD VARCHAR(64),
    email VARCHAR(64)
    );
INSERT INTO users (username,PASSWORD,email) 
VALUES("tom","123","tom@qq.com"),("lucy","123","lucy@qq.com");

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对应User类：

package domain;

public class User {
    private int id;
    private String username;
    private String password;
    private String email;

    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", password=" + password + ", email=" + email + "]";
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

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前端页面:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="/WEB2/login" method="post">
用户名：<input type="text" name="username"><br/>
密码：<input type="password" name="password"><br/>
<input type="submit" value="登录" >

</form>
</body>
</html>

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Servlet:

用到c3p0连接池，dbutils工具类，mysql驱动，注意导入相关包

utils包：

自定义连接池工具类：

package utils;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DataSourceUtils {

    private static DataSource dataSource = new ComboPooledDataSource();

    private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

    // 直接可以获取一个连接池
    public static DataSource getDataSource() {
        return dataSource;
    }

    // 获取连接对象
    public static Connection getConnection() throws SQLException {

        Connection con = tl.get();
        if (con == null) {
            con = dataSource.getConnection();
            tl.set(con);
        }
        return con;
    }

    // 开启事务
    public static void startTransaction() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.setAutoCommit(false);
        }
    }

    // 事务回滚
    public static void rollback() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.rollback();
        }
    }

    // 提交并且 关闭资源及从ThreadLocall中释放
    public static void commitAndRelease() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.commit(); // 事务提交
            con.close();// 关闭资源
            tl.remove();// 从线程绑定中移除
        }
    }

    // 关闭资源方法
    public static void closeConnection() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.close();
        }
    }

    public static void closeStatement(Statement st) throws SQLException {
        if (st != null) {
            st.close();
        }
    }

    public static void closeResultSet(ResultSet rs) throws SQLException {
        if (rs != null) {
            rs.close();
        }
    }

}

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c3p0-config.xml配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
    <default-config>
        <property name="user">root</property>
        <property name="password">xuyiqing</property>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql:///web</property>
    </default-config> 
</c3p0-config>

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核心类：

package login;

import java.io.IOException;
import java.sql.SQLException;

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

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

import domain.User;
import utils.DataSourceUtils;

public class LoginServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //1.获取用户名密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        //2.数据库中验证
        QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
        String sql = "select * from users where username=? and password=?";
        User user = null;
        try {
            user = runner.query(sql,new BeanHandler<User>(User.class) ,username,password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        if(user!=null){
            //登录成功
            response.getWriter().write(user.toString());
        }else {
            //登录失败
            response.getWriter().write("Sorry!Your username or password is wrong.");
            
        }
    }

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

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web.xml配置：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>WEB2</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>login.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
</web-app>

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完成！

访问http://localhost:8080/WEB2/login.html

输入正确的用户名和密码点击登录

结果如下：

完成！

成功！

接下来，提升功能：

统计成功登录的人数：

package login;

import java.io.IOException;
import java.sql.SQLException;

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

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

import domain.User;
import utils.DataSourceUtils;

public class LoginServlet extends HttpServlet {

    @Override
    public void init() throws ServletException {
        int count = 0;
        // 域对象
        this.getServletContext().setAttribute("count", count);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 1.获取用户名密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        // 2.数据库中验证
        QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
        String sql = "select * from users where username=? and password=?";
        User user = null;
        try {
            user = runner.query(sql, new BeanHandler<User>(User.class), username, password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        if (user != null) {
            // 登录成功
            // 利用域对象的方法
            ServletContext context = this.getServletContext();
            Integer count = (Integer) context.getAttribute("count");
            count++;
            response.getWriter().write(user.toString() + "You are the " + count + " person to log in successfully");
            context.setAttribute("count", count);
        } else {
            // 登录失败
            response.getWriter().write("Sorry!Your username or password is wrong.");

        }
    }

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

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原文地址：https://www.cnblogs.com/xuyiqing/p/8407226.html