Java简单案例：Servlet+JDBC实现登录功能
目录
- 环境说明
- Servlet+JDBC可能会遇到的坑
- web项目分层说明
- Bean层
- Dao层
- Service层
- Controller层
- Servlet 生命周期
- 登录功能代码
- 案例整体结构图
- User类
- DBUtil类
- UserDao类
- LoginServlet类
- test类
- web.xml
- index.jsp
环境说明
- mysql 5.7版本
- mysql中创建sx的数据库，在sx数据库中有一张tb_user的表
- tb_user的表中有id，username，password 三个字段
- Tomcat 9.0版本
- 通过servlet+JDBC实现登录功能
Servlet+JDBC可能会遇到的坑
- 在Servlet中使用jdbc运行报错提示java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
将mysql jar包放进tomcat服务器lib文件夹下
- 通过浏览器调用Servlet，页面显示乱码或无法显示
在调用Servlet代码中添加
request.setCharacterEncoding("utf-8");
web项目分层说明
以下是一般web项目分层说明
Bean层
Bean是实体层，里面存放实体类。通过提供符合一致性设计模式的公共方法将内部域暴露成员属性，set和get方法获取。
Dao层
Dao是持久层，访问数据库，实现数据库的真删改查。
Service层
Service是业务层，用来处理业务相关的事情。
Controller层
Controller是控制层，控制页面跳转等操作。
Servlet 生命周期
- 初始化
- 实例化
- 服务
- 销毁
登录功能代码
案例整体结构图
User类
package bean;
public class User {
public User() {
}
public User(int id, String username, String password) {
this.id = id;
this.username = username;
this.password = password;
}
public User(String username, String password) {
this.username = username;
this.password = password;
}
private int id;
private String username;
private String password;
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;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
'}';
}
}
DBUtil类
package dao.DBUtil;
import java.sql.*;
public class DBUtil {
public static Connection getConnection() throws ClassNotFoundException, SQLException {
/*加载驱动*/
Class.forName("com.mysql.jdbc.Driver");
/*创建连接*/
Connection connection=DriverManager.getConnection("jdbc:mysql://localhost:3306/sx","root","");
System.out.println("创建连接成功");
return connection;
}
public static void closeAll(ResultSet resultSet, Statement statement, Connection connection) throws SQLException {
if (resultSet!=null){
resultSet.close();
}
if (statement!=null){
statement.close();
}
if (connection!=null){
connection.close();
}
System.out.println("所有连接关闭成功");
}
}
UserDao类
这里由于是上一篇JDBC文章中修改的代码，所以大部分代码在这次是没用的。本次登录功能只用到了里面findUser方法。
package dao;
import DBUtil.DBUtil;
import bean.User;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
public class UserDao {
public List<User> findAll(){
Connection connection= null;
PreparedStatement statement= null;
ResultSet resultSet=null;
List<User> userList=new ArrayList<>();
try {
connection = DBUtil.getConnection();
String sql="SELECT * FROM tb_user";
statement = connection.prepareStatement(sql);
resultSet=statement.executeQuery();
while (resultSet.next()){
User user=new User();
user.setId(resultSet.getInt(1));
user.setUsername(resultSet.getString(2));
user.setPassword(resultSet.getString(3));
userList.add(user);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
try {
DBUtil.closeAll(resultSet,statement,connection);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
return userList;
}
public User findUser(String name){
Connection connection= null;
PreparedStatement statement= null;
ResultSet resultSet=null;
User user = new User();
try {
connection = DBUtil.getConnection();
String sql="SELECT * FROM tb_user WHERE username=?";
statement = connection.prepareStatement(sql);
statement.setString(1,name );
resultSet=statement.executeQuery();
while (resultSet.next()){
user.setId(resultSet.getInt(1));
user.setUsername(resultSet.getString(2));
user.setPassword(resultSet.getString(3));
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
try {
DBUtil.closeAll(resultSet,statement,connection);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
return user;
}
public void deleteById(int id){
Connection connection= null;
PreparedStatement statement= null;
try {
connection = DBUtil.getConnection();
String sql="DELETE FROM tb_user WHERE id=?";
statement = connection.prepareStatement(sql);
statement.setInt(1, id);
statement.executeUpdate();
System.out.println("删除成功");
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
try {
DBUtil.closeAll(null,statement,connection);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
public void add(User user){
Connection connection= null;
PreparedStatement statement= null;
try {
connection = DBUtil.getConnection();
String sql="INSERT INTO tb_user(username,password) VALUE (?,?)";
statement = connection.prepareStatement(sql);
statement.setString(1,user.getUsername());
statement.setString(2,user.getPassword());
statement.executeUpdate();
System.out.println("增加成功");
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
try {
DBUtil.closeAll(null,statement,connection);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
public void update(User user){
Connection connection= null;
PreparedStatement statement= null;
try {
connection = DBUtil.getConnection();
String sql="UPDATE tb_user SET username=?,password=? WHERE id=?";
statement = connection.prepareStatement(sql);
statement.setString(1,user.getUsername());
statement.setString(2,user.getPassword());
statement.setInt(3,user.getId());
statement.executeUpdate();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
try {
DBUtil.closeAll(null,statement,connection);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
LoginServlet类
package servlet;
import bean.User;
import dao.UserDao;
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 doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setCharacterEncoding("UTF-8");
String username=req.getParameter("username");
String password=req.getParameter("password");
UserDao userDao =new UserDao();
User user = userDao.findUser(username);
if (user.getUsername() == null){
resp.getWriter().write("用户名不存在");
}else if (!user.getPassword().equals(password)){
resp.getWriter().write("密码错误!");
}else {
resp.getWriter().write("欢迎登录");
}
}
}
test类
这个类测试是否数据库访问正常。
import bean.User;
import dao.UserDao;
import java.util.List;
public class test {
public static void main(String[] args) {
UserDao userDao =new UserDao();
String name ="test1";
User userList = userDao.findUser(name);
System.out.println(userList.getUsername());
}
}
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_4_0.xsd"
version="4.0">
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
</web-app>
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>登录</title>
</head>
<body>
<form action="/login" method="post">
username:<input name="username" type="text">
passsword:<input name="password" type="text">
<input type="submit" value="login">
</form>
</body>
</html>