JavaWeb之Servlet登录demo

简单的写一个注册和登录的demo

先介绍以下流程

（1）前台页面获取用户输入的用户名和密码

（2）将信息发送到servlet

（3）servlet进行数据库查询，返回查询的结果

首先创建一个数据库，然后其中包含用户名和密码两个字段

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`password` varchar(255) CHARACTER SET utf8mb4 DEFAULT NULL,
`username` varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('123', 'yue');
INSERT INTO `user` VALUES ('llll', '121');

　项目结构如下图

,需要导入包

前台三个页面：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>login</title>
   <style type="text/css">
#errormsg {
  color: red;
}
</style>
</head>
<body>
<c:if test="${not empty errormsg}">
  <p id="errormsg" >${errormsg }</p>
</c:if>
<form action="${pageContext.request.contextPath}/UserServlet?method=login" method="post">
  username:<input type="text" name="username" value="${username}" />
  password:<input type="password" name="password"/>
  <input type="submit" value="login" />
</form>

</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>register</title>
</head>
<body>
   <c:if test="${not empty errormsg}">
  <p id="errormsg" >${errormsg }</p>
</c:if>
<form action="${pageContext.request.contextPath}/UserServlet?method=register" method="post">
  username:<input type="text" name="username" value="${username}" />
  password:<input type="password" name="password"/>
  <input type="submit" value="register" />
</form>
</body>
</html>

succ.jsp

DBUtil,class

package com.hpe.util;

import java.io.FileReader;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

public class DBUtil {
private static String drivatename = null;
private static String url = null;
private static String username = null;
private static String password = null;

static {
  try {
   //读取配置文件，加载JDBC四大参数
   Properties config = new Properties();
   config.load(new FileReader(DBUtil.class.getClassLoader().getResource("JDBC.conf").getPath()));
   drivatename = config.getProperty("drivername");
   url = config.getProperty("url");
   username = config.getProperty("username");
   password = config.getProperty("password");

   //System.out.println(drivatename);

   //加载驱动类
   Class.forName(drivatename);
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (ClassNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
}

//建立连接
public static Connection getConn() {
  Connection conn = null;

  try {
   conn = DriverManager.getConnection(url, username, password);
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }

  return conn;
}

//关闭连接
public static void closeConn(Connection conn) {
  try {
   conn.close();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
}

//关闭preparedStatement
public static void closePstmt(PreparedStatement pstmt) {
  try {
   pstmt.close();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
}

//关闭结果集ResultSet
public static void closeRst(ResultSet rst) {
  try {
   rst.close();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
}
}

JDBC.config

drivername=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mydbjdbc
username=（用户）
password=（密码）

userServlet.java

package com.hpe.servlet;

import java.io.IOException;
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 com.hpe.po.User;
import com.hpe.service.UserService;

public class UserServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private UserService service = new UserService();

//登陆
protected void login(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    //获取用户名和密码
    String username = request.getParameter("username");
    String password = request.getParameter("password");

    //调用UserService中的方法进行验证
    User user = service.login(username, password);
    if(user != null) { //登陆成功
      //将用户信息保存在域对象中
      HttpSession session = request.getSession();
      session.setAttribute("user", user);
      //转发到成功页
      request.getRequestDispatcher("/succ.jsp").forward(request, response);
    } else { // 登陆失败
      //将错误信息、用户名放入域当中
      String errormsg = "用户名或密码错误";
      request.setAttribute("errormsg", errormsg);
      request.setAttribute("username", username);
      //转发到登陆页
      request.getRequestDispatcher("/login.jsp").forward(request, response);
    }

    }
    //注册
    protected void register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    String username = request.getParameter("username");
    String password = request.getParameter("password");

    User user = new User(username, password);

    //注册
    int result = service.register(user);
    if(result == 1) {//成功
      //将用户信息保存在域对象中
      HttpSession session = request.getSession();
      session.setAttribute("user", user);
      //转发到成功页
      request.getRequestDispatcher("/succ.jsp").forward(request, response);
    } else { //失败
      String errormsg = null;
      errormsg = "注册失败";
      if(result == -1) {//
       errormsg = "该用户已经存在";
      }
      request.setAttribute("errormsg", errormsg);
      //失败转发到注册页
      request.getRequestDispatcher("/register.jsp").forward(request, response);
    }
    }

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  //获取method参数，根据参数选择调用的方法
  String method = request.getParameter("method");
  if(method.equals("login")) {//登陆
   login(request, response);
  } else if(method.equals("register")) {//注册
   register(request, response);
  }
}

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

}

UserService.class

package com.hpe.service;

import com.hpe.dao.UserDao;
import com.hpe.po.User;

public class UserService {
   private UserDao dao = new UserDao();

   public User login(String username,String password){
    return dao.findUser(username, password);
   }

   public int register(User user){
    User u =dao.findByName(user.getUsername());
    if(u!=null){
     return -1;
    }
    int result =dao.addUser(user);
    return result;
   }
}

UserDao.class

package com.hpe.dao;

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

import com.hpe.po.User;
import com.hpe.util.DBUtil;
import java.sql.PreparedStatement;

public class UserDao {

//登录
public User findUser(String username,String password)
{
  String sql="select * from user where username=? and password=?";
  Connection conn = DBUtil.getConn();

  PreparedStatement pstmt = null;
  ResultSet rSet = null;
  User user = null;
  try {
   // 创建PreparedStatement
   pstmt = conn.prepareStatement(sql);
   // 设置参数
   pstmt.setString(1, username);
   pstmt.setString(2, password);

   rSet = pstmt.executeQuery();

   if (rSet.next()) {
    String name = rSet.getString(1);
    String pwd = rSet.getString(2);
    user = new User(name, pwd);
   }
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } finally {
   // 关闭资源先打开的后关闭
   if (rSet != null) {
    DBUtil.closeRst(rSet);
   }
   if (pstmt != null) {
    DBUtil.closePstmt(pstmt);
   }
   if (conn != null) {
    DBUtil.closeConn(conn);
   }
  }
  return user;
}

public User findByName(String username){
  String sql = "select * from user where username=?";
  // 创建连接
  Connection conn = DBUtil.getConn();

  PreparedStatement pstmt = null;
  ResultSet rSet = null;
  User user = null;
  try {
   // 创建PreparedStatement
   pstmt = conn.prepareStatement(sql);
   // 设置参数
   pstmt.setString(1, username);
   // 运行SQL语句
   /*
    * 增删改 executeUpdate() 查询 executeQuery()
    */
   rSet = pstmt.executeQuery();
   // 处理结果
   if (rSet.next()) {
    String name = rSet.getString(1);
    String pwd = rSet.getString(2);
    user = new User(name, pwd);
   }
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } finally {
   // 关闭资源先打开的后关闭
   if (rSet != null) {
    DBUtil.closeRst(rSet);
   }
   if (pstmt != null) {
    DBUtil.closePstmt(pstmt);
   }
   if (conn != null) {
    DBUtil.closeConn(conn);
   }
  }

  return user;
}

public int addUser(User user) {
  // SQL语句
  String sql = "insert into user values(?, ?)";
  // 创建连接
  Connection conn = DBUtil.getConn();

  PreparedStatement pstmt = null;
  int result = 0;

  try {
   // 创建PreparedStatement
   pstmt = conn.prepareStatement(sql);
   // 设置参数
   pstmt.setString(1, user.getUsername());
   pstmt.setString(2, user.getPassword());
   // 运行SQL语句
   /*
    * 增删改 executeUpdate() 查询 executeQuery()
    */
   result = pstmt.executeUpdate();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } finally {
   // 关闭资源先打开的后关闭
   if (pstmt != null) {
    DBUtil.closePstmt(pstmt);
   }
   if (conn != null) {
    DBUtil.closeConn(conn);
   }
  }
  return result;
}
}

package com.hpe.po;

public class User {
private String username;
private String password;

public User(){

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

}

本人是一个菜鸟，如有不当或错误之处，欢迎指正