mybatis+foreach

MyBatis的`foreach`标签用于在SQL语句中遍历一个集合，并将集合中的元素作为参数传递给SQL语句。下面是一个示例：

<delete id="deleteUsersByIds" parameterType="java.util.List">
  DELETE FROM users WHERE id IN
  <foreach collection="list" item="item" index="index" open="(" separator="," close=")">
    #{item}
  </foreach>
</delete>

在上面的示例中，`foreach`标签迭代了一个名为`list`的集合，并将集合中的每个元素以`${item}`的形式插入到SQL语句中。

相关问题

mybatis+批量插入去重

以下是使用MyBatis实现批量插入去重的步骤：

1.在Mapper.xml文件中定义插入语句，使用INSERT IGNORE INTO语句插入数据，忽略重复数据的插入。

<insert id="batchInsert" parameterType="java.util.List">
    INSERT IGNORE INTO table_name (column1, column2, ...) VALUES
    <foreach collection="list" item="item" separator=",">
        (#{item.column1}, #{item.column2}, ...)
    </foreach>
</insert>

2.在Service层中，将数据按照一定的批次进行分割，然后调用Mapper中的批量插入方法。

@Service
public class MyService {
    @Autowired
    private MyMapper myMapper;

    public void batchInsert(List<MyEntity> list) {
        int batchSize = 1000;
        int totalSize = list.size();
        int batchCount = (totalSize + batchSize - 1) / batchSize;
        for (int i = 0; i < batchCount; i++) {
            int fromIndex = i * batchSize;
            int toIndex = Math.min((i + 1) * batchSize, totalSize);
            List<MyEntity> subList = list.subList(fromIndex, toIndex);
            myMapper.batchInsert(subList);
        }
    }
}

3.在Controller层中，接收请求并调用Service层的批量插入方法。

@RestController
public class MyController {
    @Autowired
    private MyService myService;

    @PostMapping("/batchInsert")
    public void batchInsert(@RequestBody List<MyEntity> list) {
        myService.batchInsert(list);
    }
}

springboot+mybatis+mysql+jsp实现用户登陆、增删改查的样例代码

以下是一个简单的Spring Boot + MyBatis + MySQL + JSP实现用户登录、增删改查的样例代码：

1. 首先，需要在pom.xml文件中添加以下依赖：

<dependencies>
    <!-- Spring Boot -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- MyBatis -->
    <dependency>
        <groupId>org.mybatis.spring.boot</groupId>
        <artifactId>mybatis-spring-boot-starter</artifactId>
        <version>2.1.4</version>
    </dependency>

    <!-- MySQL -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.23</version>
    </dependency>

    <!-- JSP -->
    <dependency>
        <groupId>org.apache.tomcat.embed</groupId>
        <artifactId>tomcat-embed-jasper</artifactId>
        <scope>provided</scope>
    </dependency>
</dependencies>

2. 在application.properties文件中添加以下配置：

spring.datasource.url=jdbc:mysql://localhost:3306/mydb?useSSL=false&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

mybatis.mapper-locations=classpath:mapper/*.xml
mybatis.type-aliases-package=com.example.demo.entity

3. 创建一个User实体类：

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

4. 创建一个UserMapper接口：

@Mapper
public interface UserMapper {
    User selectUserByUsername(String username);
    List<User> selectAllUsers();
    void insertUser(User user);
    void updateUser(User user);
    void deleteUser(Integer id);
}

5. 创建一个UserMapper.xml文件：

<mapper namespace="com.example.demo.mapper.UserMapper">
    <select id="selectUserByUsername" resultType="com.example.demo.entity.User">
        select * from user where username = #{username}
    </select>

    <select id="selectAllUsers" resultType="com.example.demo.entity.User">
        select * from user
    </select>

    <insert id="insertUser">
        insert into user (username, password) values (#{username}, #{password})
    </insert>

    <update id="updateUser">
        update user set username = #{username}, password = #{password} where id = #{id}
    </update>

    <delete id="deleteUser">
        delete from user where id = #{id}
    </delete>
</mapper>

6. 创建一个UserController类：

@Controller
public class UserController {
    @Autowired
    private UserMapper userMapper;

    @GetMapping("/")
    public String index() {
        return "index";
    }

    @GetMapping("/login")
    public String login() {
        return "login";
    }

    @PostMapping("/login")
    public String login(String username, String password, HttpSession session) {
        User user = userMapper.selectUserByUsername(username);
        if (user != null && user.getPassword().equals(password)) {
            session.setAttribute("user", user);
            return "redirect:/user/list";
        } else {
            return "login";
        }
    }

    @GetMapping("/logout")
    public String logout(HttpSession session) {
        session.removeAttribute("user");
        return "redirect:/login";
    }

    @GetMapping("/user/list")
    public String list(Model model) {
        List<User> userList = userMapper.selectAllUsers();
        model.addAttribute("userList", userList);
        return "list";
    }

    @GetMapping("/user/add")
    public String add() {
        return "add";
    }

    @PostMapping("/user/add")
    public String add(User user) {
        userMapper.insertUser(user);
        return "redirect:/user/list";
    }

    @GetMapping("/user/edit/{id}")
    public String edit(@PathVariable Integer id, Model model) {
        User user = userMapper.selectUserById(id);
        model.addAttribute("user", user);
        return "edit";
    }

    @PostMapping("/user/edit")
    public String edit(User user) {
        userMapper.updateUser(user);
        return "redirect:/user/list";
    }

    @GetMapping("/user/delete/{id}")
    public String delete(@PathVariable Integer id) {
        userMapper.deleteUser(id);
        return "redirect:/user/list";
    }
}

7. 创建以下JSP页面：

index.jsp：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>首页</title>
</head>
<body>
    <h1>欢迎来到首页</h1>
    <a href="/login">登录</a>
</body>
</html>

login.jsp：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>登录</title>
</head>
<body>
    <h1>登录</h1>
    <form method="post" action="/login">
        <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>

list.jsp：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>用户列表</title>
</head>
<body>
    <h1>用户列表</h1>
    <a href="/user/add">添加用户</a>
    <table border="1">
        <tr>
            <th>ID</th>
            <th>用户名</th>
            <th>密码</th>
            <th>操作</th>
        </tr>
        <c:forEach items="${userList}" var="user">
            <tr>
                <td>${user.id}</td>
                <td>${user.username}</td>
                <td>${user.password}</td>
                <td>
                    <a href="/user/edit/${user.id}">编辑</a>
                    <a href="/user/delete/${user.id}">删除</a>
                </td>
            </tr>
        </c:forEach>
    </table>
    <a href="/logout">退出登录</a>
</body>
</html>

add.jsp：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>添加用户</title>
</head>
<body>
    <h1>添加用户</h1>
    <form method="post" action="/user/add">
        <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="添加">
    </form>
    <a href="/user/list">返回列表</a>
</body>
</html>

edit.jsp：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>编辑用户</title>
</head>
<body>
    <h1>编辑用户</h1>
    <form method="post" action="/user/edit">
        <input type="hidden" name="id" value="${user.id}">
        <label>用户名：</label>
        <input type="text" name="username" value="${user.username}"><br>
        <label>密码：</label>
        <input type="password" name="password" value="${user.password}"><br>
        <input type="submit" value="保存">
    </form>
    <a href="/user/list">返回列表</a>
</body>
</html>

8. 运行程序，访问http://localhost:8080即可看到首页。点击登录，输入用户名和密码即可进入用户列表页面，可以进行增删改查操作。