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】

 1 <!DOCTYPE html>
 2 <html>
 3   <head>
 4     <title>login.html</title>
 5     <meta charset="utf-8">
 6     <meta name="keywords" content="keyword1,keyword2,keyword3">
 7     <meta name="description" content="this is my page">
 8     <meta name="content-type" content="text/html; charset=UTF-8">
 9     
10     <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
11 
12   </head>
13   
14   <body>
15       <form action="UserLogin">
16           用户名：<input type="text" name="uname" id="uname" /><br>
17           密码：<input type="password" name="pwd" id="pwd" /><br>
18           <input value="登录" type="submit"/>
19       </form>
20   </body>
21 </html>
View Code

success.html【登录成功界面】

 1 <!DOCTYPE html>
 2 <html>
 3   <head>
 4     <title>success.html</title>
 5     <meta charset="utf-8">
 6     <meta name="keywords" content="keyword1,keyword2,keyword3">
 7     <meta name="description" content="this is my page">
 8     <meta name="content-type" content="text/html; charset=UTF-8">
 9     
10     <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
11 
12   </head>
13   
14   <body>
15     This is 登录成功  page.看到女神<br>
16     <div>
17     <img src="imges/success.jpg"  width="800px" height="500px"/>
18     </div>
19   </body>
20 </html>
View Code

error.html【登录失败界面】

 1 <!DOCTYPE html>
 2 <html>
 3   <head>
 4     <title>error.html</title>
 5     <meta charset="utf-8">
 6     <meta name="keywords" content="keyword1,keyword2,keyword3">
 7     <meta name="description" content="this is my page">
 8     <meta name="content-type" content="text/html; charset=UTF-8">
 9     
10     <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
11 
12   </head>
13   
14   <body>
15     This is 登录失败  page.一直在转悠转悠 <br>
16     <div>
17         <img src="imges/error.gif" />
18     </div>
19   </body>
20 </html>
View Code

entity层【实体类】

 1 package boom.servlet.entity;
 2 /**
 3  * 实体类
 4  * @author Administrator
 5  *
 6  */
 7 public class T_user {
 8     // 对应着数据库表的字段
 9     private int id;
10     private String name;
11     private String pwd;
12     // 无参构造方法
13     public T_user() {
14     }
15     // 有参构造方法
16     public T_user(int id, String name, String pwd) {
17         super();
18         this.id = id;
19         this.name = name;
20         this.pwd = pwd;
21     }
22     // getter setter
23     public int getId() {
24         return id;
25     }
26     public void setId(int id) {
27         this.id = id;
28     }
29     public String getName() {
30         return name;
31     }
32     public void setName(String name) {
33         this.name = name;
34     }
35     public String getPwd() {
36         return pwd;
37     }
38     public void setPwd(String pwd) {
39         this.pwd = pwd;
40     }
41     // 重写toString
42     @Override
43     public String toString() {
44         return "T_user [id=" + id + ", name=" + name + ", pwd=" + pwd + "]";
45     }
46     
47 }
View Code

util层【封装的JDBC数据库连接】

  1 package boom.servlet.util;
  2 
  3 import java.io.IOException;
  4 import java.io.InputStream;
  5 import java.sql.Connection;
  6 import java.sql.DriverManager;
  7 import java.sql.PreparedStatement;
  8 import java.sql.ResultSet;
  9 import java.sql.SQLException;
 10 import java.sql.Statement;
 11 import java.util.Properties;
 12 /**
 13  * 连接数据库的工具类
 14  * @author Administrator
 15  *
 16  */
 17 public class DBUtil {
 18     private static String driver;
 19     private static String url;
 20     private static String username;
 21     private static String password;
 22 
 23     static {
 24         // 创建properties对象获取属性文件的内容
 25         Properties p = new Properties();
 26         // 获取属性配置文件的读取流对象
 27         InputStream is = DBUtil.class.getResourceAsStream("/db.properties");
 28         try {
 29             // 加载属性配置文件
 30             p.load(is);
 31             // 获取jdbc参数
 32             driver = p.getProperty("driver");
 33             url = p.getProperty("url");
 34             username = p.getProperty("username");
 35             password = p.getProperty("password");
 36             // 加载驱动
 37             Class.forName(driver);
 38         } catch (IOException e) {
 39             e.printStackTrace();
 40         } catch (ClassNotFoundException e) {
 41             // TODO Auto-generated catch block
 42             e.printStackTrace();
 43         }
 44     }
 45 
 46     // 获取Connection对象
 47     public static Connection getConnection() {
 48         Connection conn = null;
 49         try {
 50             conn = DriverManager.getConnection(url, username, password);
 51         } catch (SQLException e) {
 52             e.printStackTrace();
 53         }
 54         return conn;
 55     }
 56 
 57     // 封装获取PreparedStatement对象
 58     public static PreparedStatement getPreparedStatement(String sql,
 59             Connection conn) {
 60 
 61         PreparedStatement ps = null;
 62         try {
 63             ps = conn.prepareStatement(sql);
 64         } catch (SQLException e) {
 65             // TODO Auto-generated catch block
 66             e.printStackTrace();
 67         }
 68         return ps;
 69 
 70     }
 71 
 72     // 封装获取Statement对象
 73     public static Statement getStatement(Connection conn) {
 74         Statement stmt = null;
 75         try {
 76             stmt = conn.createStatement();
 77         } catch (SQLException e) {
 78             e.printStackTrace();
 79         }
 80         return stmt;
 81 
 82     }
 83 
 84     // 关闭资源
 85     //父类可以调用 子类继承过的父类方法
 86     public static void closeAll(ResultSet rs, Statement ps, Connection conn) {
 87         try {
 88             if(rs!=null ){
 89                 rs.close();
 90             }
 91         } catch (SQLException e1) {
 92             e1.printStackTrace();
 93         }
 94         try {
 95             if(ps!=null ){
 96                 ps.close();
 97             }
 98         } catch (SQLException e) {
 99                 e.printStackTrace();
100         }
101         try {
102             if(conn!=null){
103                 conn.close();
104             }
105         } catch (SQLException e) {
106             e.printStackTrace();
107         }
108     }
109     // 封装DML
110     public static int executeDML(String sql, Object... objs) {
111         // 创建连接对象
112         Connection conn = getConnection();
113         // 创建sql命令对象
114         PreparedStatement ps = DBUtil.getPreparedStatement(sql, conn);
115         // 给占位符赋值
116         try {
117             conn.setAutoCommit(false);
118             for (int i = 0; i < objs.length; i++) {
119                 ps.setObject(i + 1, objs[i]);
120             }
121             int i = ps.executeUpdate();
122             conn.commit();
123             return i;
124         } catch (Exception e) {
125             try {
126                 conn.rollback();
127             } catch (SQLException e1) {
128                 // TODO Auto-generated catch block
129                 e1.printStackTrace();
130             }
131         } finally {
132             // 关闭资源
133             DBUtil.closeAll(null, ps, conn);
134         }
135         // 返回结果
136         return -1;
137     }
138     // 测试数据库是否连接成功
139     public static void main(String[] args) {
140         Connection conn = DBUtil.getConnection();
141         System.out.println(conn);
142     }
143 }
View Code

dao层【user实现类】

 1 package boom.servlet.dao;
 2 
 3 import java.sql.Connection;
 4 import java.sql.PreparedStatement;
 5 import java.sql.ResultSet;
 6 import java.sql.SQLException;
 7 
 8 import boom.servlet.entity.T_user;
 9 import boom.servlet.util.DBUtil;
10 
11 /**
12  * 登录查询实现类
13  * @author Administrator
14  *select * from t_user where name='admin' and pwd='admin'
15  */
16 public class UserDaoImpl {
17     // 返回对象
18     public T_user getUser(String name,String pwd){
19         String sql = "select * from t_user  where name=? and pwd =? ";
20         Connection conn = null;
21         PreparedStatement  ps = null;
22         ResultSet rs = null;
23         T_user user=  null;
24         //1.创建连接
25         conn = DBUtil.getConnection();
26         try {
27               //2.获取预处理块对象  preparestatement
28               ps = conn.prepareStatement(sql);
29               //3.绑定参数
30               ps.setString(1, name);
31               ps.setString(2, pwd);
32               //4.执行SQL语句  5.获取结果集
33                rs = ps.executeQuery();
34               //6.遍历结果集存放到 user对象中
35                while(rs.next()){
36                    int id = rs.getInt("id");
37                    String name2 = rs.getString("name");
38                    String pwd2 = rs.getString("pwd");
39                    //将数据放到对象中
40                    user = new T_user(id,name2,pwd2);
41                }
42         } catch (SQLException e) {
43             e.printStackTrace();
44         }finally{
45             //7.关闭资源
46             DBUtil.closeAll(rs, ps, conn);
47         }
48         return user;
49     }
50 }
View Code

servlet层【获取前端页面登录验证】

 1 package boom.servlet.servlet;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.ServletException;
 6 import javax.servlet.http.HttpServlet;
 7 import javax.servlet.http.HttpServletRequest;
 8 import javax.servlet.http.HttpServletResponse;
 9 
10 import boom.servlet.dao.UserDaoImpl;
11 import boom.servlet.entity.T_user;
12 /**
13  * 获取前端页面登录验证
14  * @author Administrator
15  *
16  */
17 public class UserLogin extends HttpServlet {
18     @Override
19     protected void service(HttpServletRequest request,
20             HttpServletResponse response) throws ServletException, IOException {
21         // 1、获取login用户提交的数据【账户，密码】
22         String uname = request.getParameter("uname");
23         String pwd = request.getParameter("pwd");
24         // 2、调用业务逻辑层。简化后调用dao层
25         UserDaoImpl daoImpl = new UserDaoImpl();
26         T_user user = daoImpl.getUser(uname, pwd);
27         String path = "/login.html";
28         if (user != null) {
29             path = "/success.html";
30         } else {
31             path = "/error.html";
32         }
33         // 3 根据dao的查询结果 ，跳转到成功或失败页面
34         request.getRequestDispatcher(path).forward(request, response);
35 
36     }
37 }
View Code

test层【测试dao层是否连接成功】

 1 package boom.servlet.test;
 2 
 3 import boom.servlet.dao.UserDaoImpl;
 4 import boom.servlet.entity.T_user;
 5 
 6 /**
 7  * 测试dao层
 8  * @author Administrator
 9  *
10  */
11 public class TestUserDao {
12     public static void main(String[] args) {
13         UserDaoImpl daoImpl = new UserDaoImpl();
14         T_user user = daoImpl.getUser("boom", "123");
15         if(user != null){
16             System.out.println("登录成功");
17         }else{
18             System.out.println("登录失败");
19         }
20     }
21 }
View Code

数据库配置文件【db.properties】

演示界面：



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原文地址：https://www.cnblogs.com/cao-yin/p/9899665.html