用ssm写一个登录界面

好的，下面我将为你提供一个简单的SSM登录界面的实现步骤：

1. 创建一个Maven项目，引入所需的依赖。在pom.xml文件中添加以下依赖：

<!-- Spring -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.2.7.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.2.7.RELEASE</version>
</dependency>

<!-- MyBatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.5</version>
</dependency>
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis-spring</artifactId>
    <version>2.0.5</version>
</dependency>

<!-- 数据库连接池 -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.12</version>
</dependency>

<!-- JSP -->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>jstl</artifactId>
    <version>1.2</version>
</dependency>
<dependency>
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
</dependency>

<!-- Servlet -->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>servlet-api</artifactId>
    <version>2.5</version>
</dependency>

<!-- Junit -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>

2. 配置数据源和MyBatis。

在src/main/resources目录下创建db.properties文件，配置数据源信息。例如：

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test
jdbc.username=root
jdbc.password=123456

在src/main/resources目录下创建mybatis-config.xml文件，配置MyBatis。例如：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
        <package name="com.example.entity"/>
    </typeAliases>
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

3. 创建实体类和DAO层。

在com.example.entity包下创建User实体类，例如：

public class User {
    private Integer id;
    private String username;
    private String password;
    // getter和setter方法
}

在com.example.dao包下创建UserMapper接口和UserMapper.xml文件。例如：

UserMapper.java

public interface UserMapper {
    User selectByUsernameAndPassword(@Param("username") String username, @Param("password") String password);
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.dao.UserMapper">
    <select id="selectByUsernameAndPassword" resultType="com.example.entity.User">
        select * from user where username = #{username} and password = #{password}
    </select>
</mapper>

4. 创建Service层和Controller层。

在com.example.service包下创建UserService接口和UserServiceImpl实现类。例如：

UserService.java

public interface UserService {
    User login(String username, String password);
}

UserServiceImpl.java

@Service
public class UserServiceImpl implements UserService {

    @Autowired
    private UserMapper userMapper;

    @Override
    public User login(String username, String password) {
        return userMapper.selectByUsernameAndPassword(username, password);
    }
}

在com.example.controller包下创建LoginController类。例如：

@Controller
@RequestMapping("/login")
public class LoginController {

    @Autowired
    private UserService userService;

    @RequestMapping("/login")
    public String login(String username, String password, HttpSession session) {
        User user = userService.login(username, password);
        if (user != null) {
            session.setAttribute("user", user);
            return "redirect:/index.jsp";
        } else {
            return "redirect:/login.jsp";
        }
    }

    @RequestMapping("/logout")
    public String logout(HttpSession session) {
        session.invalidate();
        return "redirect:/login.jsp";
    }
}

5. 创建登录页面和主页。

在WebRoot目录下创建login.jsp和index.jsp页面。例如：

login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
    <title>登录</title>
</head>
<body>
<h1>登录</h1>
<form action="${pageContext.request.contextPath}/login/login" method="post">
    <label>用户名：</label>
    <input type="text" name="username"/><br/>
    <label>密码：</label>
    <input type="password" name="password"/><br/>
    <input type="submit" value="登录"/>
</form>
</body>
</html>

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8" session="false"%>
<!DOCTYPE html>
<html>
<head>
    <title>首页</title>
</head>
<body>
<h1>欢迎您，${user.username}！</h1>
<a href="${pageContext.request.contextPath}/login/logout">退出</a>
</body>
</html>

至此，一个简单的SSM登录界面就完成了。