Servlet登录小案例

需求：
登录功能 
登录页面输入用户名和密码， 到数据库进行验证 ，如果成功跳转到success.html页面，失败跳转到error.html页面
数据库 mysql，数据表 t_user表【表中的字段 ：name 用户名，pwd 密码】
实现：
mysql 存储数据建表 
jdbc操作java代码连接查询数据库里对应的字段
servlet将 html和java连接起来，用login来登录转发到成功或者失败页面。
实现步骤：
jdbc 
依赖 jar包，数据库连接的util DBUtil数据库连接工具类
mysql 连接
db.properties 数据库连接配置
核心代码实现：（DAO层）
sql语句 查询：String sql = "select * from t_user  where name=? and pwd =? ";
创建一个实体类和数据库表对应，dao层 用户名和密码验证，返回一个结果 对象 
servlet调用DAO层：如果用户存在 ，不为空，跳转到ok.html页面 ；如果不存在，对象为空， 登录失败 error.html

前台页面：
login.html【登录界面】

 <!DOCTYPE html>
 <html>
   <head>
     <title>login.html</title>
     <meta charset="utf-8">
     <meta name="keywords" content="keyword1,keyword2,keyword3">
     <meta name="description" content="this is my page">
     <meta name="content-type" content="text/html; charset=UTF-8">

     <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

   </head>

   <body>
       <form action="UserLogin">
           用户名：<input type="text" name="uname" id="uname" /><br>
           密码：<input type="password" name="pwd" id="pwd" /><br>
           <input value="登录" type="submit"/>
       </form>
   </body>
 </html>

success.html【登录成功界面】

 <!DOCTYPE html>
 <html>
   <head>
     <title>success.html</title>
     <meta charset="utf-8">
     <meta name="keywords" content="keyword1,keyword2,keyword3">
     <meta name="description" content="this is my page">
     <meta name="content-type" content="text/html; charset=UTF-8">

     <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

   </head>

   <body>
     This is 登录成功  page.看到女神<br>
     <div>
     <img src="imges/success.jpg"  width="800px" height="500px"/>
     </div>
   </body>
 </html>

error.html【登录失败界面】

 <!DOCTYPE html>
 <html>
   <head>
     <title>error.html</title>
     <meta charset="utf-8">
     <meta name="keywords" content="keyword1,keyword2,keyword3">
     <meta name="description" content="this is my page">
     <meta name="content-type" content="text/html; charset=UTF-8">

     <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

   </head>

   <body>
     This is 登录失败  page.一直在转悠转悠 <br>
     <div>
         <img src="imges/error.gif" />
     </div>
   </body>
 </html>

entity层【实体类】

 package boom.servlet.entity;
 /**
  * 实体类
  * @author Administrator
  *
  */
 public class T_user {
     // 对应着数据库表的字段
     private int id;
     private String name;
     private String pwd;
     // 无参构造方法
     public T_user() {
     }
     // 有参构造方法
     public T_user(int id, String name, String pwd) {
         super();
         this.id = id;
         this.name = name;
         this.pwd = pwd;
     }
     // getter setter
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public String getPwd() {
         return pwd;
     }
     public void setPwd(String pwd) {
         this.pwd = pwd;
     }
     // 重写toString
     @Override
     public String toString() {
         return "T_user [id=" + id + ", name=" + name + ", pwd=" + pwd + "]";
     }

 }

util层【封装的JDBC数据库连接】

 package boom.servlet.util;

 import java.io.IOException;
 import java.io.InputStream;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Properties;
 /**
  * 连接数据库的工具类
  * @author Administrator
  *
  */
 public class DBUtil {
     private static String driver;
     private static String url;
     private static String username;
     private static String password;

     static {
         // 创建properties对象获取属性文件的内容
         Properties p = new Properties();
         // 获取属性配置文件的读取流对象
         InputStream is = DBUtil.class.getResourceAsStream("/db.properties");
         try {
             // 加载属性配置文件
             p.load(is);
             // 获取jdbc参数
             driver = p.getProperty("driver");
             url = p.getProperty("url");
             username = p.getProperty("username");
             password = p.getProperty("password");
             // 加载驱动
             Class.forName(driver);
         } catch (IOException e) {
             e.printStackTrace();
         } catch (ClassNotFoundException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

     // 获取Connection对象
     public static Connection getConnection() {
         Connection conn = null;
         try {
             conn = DriverManager.getConnection(url, username, password);
         } catch (SQLException e) {
             e.printStackTrace();
         }
         return conn;
     }

     // 封装获取PreparedStatement对象
     public static PreparedStatement getPreparedStatement(String sql,
             Connection conn) {

         PreparedStatement ps = null;
         try {
             ps = conn.prepareStatement(sql);
         } catch (SQLException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         return ps;

     }

     // 封装获取Statement对象
     public static Statement getStatement(Connection conn) {
         Statement stmt = null;
         try {
             stmt = conn.createStatement();
         } catch (SQLException e) {
             e.printStackTrace();
         }
         return stmt;

     }

     // 关闭资源
     //父类可以调用 子类继承过的父类方法
     public static void closeAll(ResultSet rs, Statement ps, Connection conn) {
         try {
             if(rs!=null ){
                 rs.close();
             }
         } catch (SQLException e1) {
             e1.printStackTrace();
         }
         try {
             if(ps!=null ){
                 ps.close();
             }
         } catch (SQLException e) {
                 e.printStackTrace();
         }
         try {
             if(conn!=null){
                 conn.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
     // 封装DML
     public static int executeDML(String sql, Object... objs) {
         // 创建连接对象
         Connection conn = getConnection();
         // 创建sql命令对象
         PreparedStatement ps = DBUtil.getPreparedStatement(sql, conn);
         // 给占位符赋值
         try {
             conn.setAutoCommit(false);
             for (int i = 0; i < objs.length; i++) {
                 ps.setObject(i + 1, objs[i]);
             }
             int i = ps.executeUpdate();
             conn.commit();
             return i;
         } catch (Exception e) {
             try {
                 conn.rollback();
             } catch (SQLException e1) {
                 // TODO Auto-generated catch block
                 e1.printStackTrace();
             }
         } finally {
             // 关闭资源
             DBUtil.closeAll(null, ps, conn);
         }
         // 返回结果
         return -1;
     }
     // 测试数据库是否连接成功
     public static void main(String[] args) {
         Connection conn = DBUtil.getConnection();
         System.out.println(conn);
     }
 }

dao层【user实现类】

 package boom.servlet.dao;

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

 import boom.servlet.entity.T_user;
 import boom.servlet.util.DBUtil;

 /**
  * 登录查询实现类
  * @author Administrator
  *select * from t_user where name='admin' and pwd='admin'
  */
 public class UserDaoImpl {
     // 返回对象
     public T_user getUser(String name,String pwd){
         String sql = "select * from t_user  where name=? and pwd =? ";
         Connection conn = null;
         PreparedStatement  ps = null;
         ResultSet rs = null;
         T_user user=  null;
         //1.创建连接
         conn = DBUtil.getConnection();
         try {
               //2.获取预处理块对象  preparestatement
               ps = conn.prepareStatement(sql);
               //3.绑定参数
               ps.setString(1, name);
               ps.setString(2, pwd);
               //4.执行SQL语句  5.获取结果集
                rs = ps.executeQuery();
               //6.遍历结果集存放到 user对象中
                while(rs.next()){
                    int id = rs.getInt("id");
                    String name2 = rs.getString("name");
                    String pwd2 = rs.getString("pwd");
                    //将数据放到对象中
                    user = new T_user(id,name2,pwd2);
                }
         } catch (SQLException e) {
             e.printStackTrace();
         }finally{
             //7.关闭资源
             DBUtil.closeAll(rs, ps, conn);
         }
         return user;
     }
 }

servlet层【获取前端页面登录验证】

 package boom.servlet.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 boom.servlet.dao.UserDaoImpl;
 import boom.servlet.entity.T_user;
 /**
  * 获取前端页面登录验证
  * @author Administrator
  *
  */
 public class UserLogin extends HttpServlet {
     @Override
     protected void service(HttpServletRequest request,
             HttpServletResponse response) throws ServletException, IOException {
         // 1、获取login用户提交的数据【账户，密码】
         String uname = request.getParameter("uname");
         String pwd = request.getParameter("pwd");
         // 2、调用业务逻辑层。简化后调用dao层
         UserDaoImpl daoImpl = new UserDaoImpl();
         T_user user = daoImpl.getUser(uname, pwd);
         String path = "/login.html";
         if (user != null) {
             path = "/success.html";
         } else {
             path = "/error.html";
         }
         // 3 根据dao的查询结果 ，跳转到成功或失败页面
         request.getRequestDispatcher(path).forward(request, response);

     }
 }

test层【测试dao层是否连接成功】

 package boom.servlet.test;

 import boom.servlet.dao.UserDaoImpl;
 import boom.servlet.entity.T_user;

 /**
  * 测试dao层
  * @author Administrator
  *
  */
 public class TestUserDao {
     public static void main(String[] args) {
         UserDaoImpl daoImpl = new UserDaoImpl();
         T_user user = daoImpl.getUser("boom", "123");
         if(user != null){
             System.out.println("登录成功");
         }else{
             System.out.println("登录失败");
         }
     }
 }

数据库配置文件【db.properties】

演示界面：