登录案例的需求分析以及代码实现

用户登录案例需求：

　　1.编写login.html登录页面

　　　　username & password 两个输入框

　　2.使用Druid数据库连接池技术,操作mysql，day14数据库中user表

　　3.使用JdbcTemplate技术封装JDBC

　　4.登录成功跳转到SuccessServlet展示：登录成功！用户名,欢迎您

　　5.登录失败跳转到FailServlet展示：登录失败，用户名或密码错误

开发步骤：

　　1、创建项目，导入html文件、配置文件、jar包

　　druid.properties配置文件:

driverClassName=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/day14
username=root
password=root
initialSize=5
maxActive=10
maxWait=3000

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="" 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>

　　2、创建数据库环境

CREATE DATABASE day14;
USE day14;
CREATE TABLE USER(
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(32) UNIQUE NOT NULL,
    PASSWORD VARCHAR(32) NOT NULL
);

　　3、创建User类

/**
 * 用户的实体类
 */
public class User {
    private int id;
    private String username;
    private String password;

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + 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;
    }

    public User() {
    }

    public User(int id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }
}

　　4、编写JDBCUtils工具类

/**
 * JDBC工具类，使用Druid连接池
 */
public class JDBCUtils {
    private static DataSource ds;

    static {
        try {
            //1、加载配置文件
            Properties pro = new Properties();
            //使用ClassLoader加载配置文件，获取字节输入流
            InputStream is = JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties");
            pro.load(is);

            //2、初始化连接池对象
            ds = DruidDataSourceFactory.createDataSource(pro);

        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 获取连接池对象
     */
    public static DataSource getDataSource(){
        return ds;
    }

    /**
     * 获取连接Connection对象
     */
    public static Connection getConnection() throws SQLException {
        return ds.getConnection();
    }
}

　　5、创建包dao，创建UserDao类，提供login方法

/**
 * 操作数据库中User表的类
 */
public class UserDao {
    //声明JdbcTemplate对象共用
    private JdbcTemplate template = new JdbcTemplate(JDBCUtils.getDataSource());

    /**
     * 登陆方法
     * @param loginUser
     * @return
     */
    public User login(User loginUser){
        try {
            //编写sql
            String sql = "select * from USER where username = ? and password = ?";
            //调用query方法
            User user = template.queryForObject(sql,
                            new BeanPropertyRowMapper<>(User.class),
                            loginUser.getUsername(), loginUser.getPassword());
            return user;
        } catch (DataAccessException e) {
            e.printStackTrace();
            return null;
        }
    }
}

　　6、编写LoginServlet类

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1、设置编码
        req.setCharacterEncoding("UTF-8");
        //2、获取请求参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        //3、封账user对象
        User loginuser = new User();
        loginuser.setUsername(username);
        loginuser.setPassword(password);
        //4、调用UserDao的login方法
        UserDao userDao = new UserDao();
        User user = userDao.login(loginuser);
        //5、判断user
        if (user==null){
            //登陆失败
            req.getRequestDispatcher("/failServlet").forward(req,resp);
        }else {
            //登陆成功
            //存储数据
            req.setAttribute("user",user);
            //转发
            req.getRequestDispatcher("/successServlet").forward(req,resp);
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

　　7、login.html中form表单的action路径的写法

　　　　虚拟目录+Servlet的资源路径

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="/loginServlet" 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>

　　8、编写SuccessServlet登陆成功页面和FailServlet登陆失败页面

　　SuccessServlet登陆成功页面：

@WebServlet("/successServlet")
public class SuccessServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取Request域中共享的user对象
        User user = (User) req.getAttribute("user");
        if (user!=null){
            //给页面写一句话
            resp.setContentType("text/html;charset=utf-8");
            //输出
            resp.getWriter().write("登陆成功!"+user.getUsername()+",欢迎您");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

　　FailServlet登陆失败页面：

@WebServlet("/failServlet")
public class FailServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //给页面写一句话
        resp.setContentType("text/html;charset=utf-8");
        //输出
        resp.getWriter().write("登陆失败，用户名或密码错误");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}