05-Mybatis注解开发（Mybatis系列终结篇）

2023-12-16 18:38:39

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05-Mybatis注解开发（Mybatis系列终结篇）

使用注解开发，可以减少Mapper映射文件的编写。

1、Mybatis常用注解

@Insert:实现新增

@Update:实现更新

@Delete:实现删除

@Select:实现查询

@Result:实现结果集封装

@Results:可以与@Result 一起使用，封装多个结果集

@ResultMap:实现引用@Results 定义的封装

@One:实现一对一结果集封装

@Many:实现一对多结果集封装

@SelectProvider: 实现动态 SQL 映射

@CacheNamespace:实现注解二级缓存的使用

2、使用注解实现基本CRUD

2.1、主配置文件

<configuration>
  <!-- 引入外部配置文件 -->
  <properties resource="jdbc.properties"/>

  <!-- 实体类别名配置 -->
  <typeAliases>
    <package name="com.junlong.domain"/>
  </typeAliases>

  <!-- 环境配置 -->
  <environments default="mysql">
    <environment id="mysql">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${jdbc.driver}"/>
        <property name="url" value="${jdbc.url}"/>
        <property name="username" value="${jdbc.username}"/>
        <property name="password" value="${jdbc.password}"/>
      </dataSource>
    </environment>
  </environments>

  <!-- 持久层接口配置 -->
  <mappers>
    <package name="com.junlong.dao"/>
  </mappers>
</configuration>

2.2、持久层接口（注解开发）

public interface UserDao {
    /**
     * 查询所有用户
     *
     * @return 返回所有用户列表 List<User>
     */
    @Select("select * from user")
    @Results(
        id = "userMap",
        value = {
            @Result(id = true, column = "id", property = "userId"),
            @Result(column = "username", property = "userName"),
            @Result(column = "birthday", property = "userBirthday"),
            @Result(column = "sex", property = "userSex"),
            @Result(column = "address", property = "userAddress")
        }
    )
    List<User> findAll();

    /**
     * 根据用户id查询用户信息
     *
     * @param id 用户id
     * @return 返回用户对象 User
     */
    @Select("select * from user where id = #{id}")
    @ResultMap("userMap")
    User findById(int id);

    /**
     * 新增用户
     *
     * @param user 用户对象
     */
    @Insert("insert into user (username, birthday, sex, address) VALUES (#{userName}, #{userBirthday}, #{userSex}, #{userAddress})")
    @SelectKey(keyColumn = "id", keyProperty = "userId", resultType = Integer.class, before = false, statement = "select last_insert_id()")
    void saveUser(User user);

    /**
     * 更新用户信息
     *
     * @param user 用户对象
     */
    @Update("update user set username = #{userName}, address = #{userAddress}, birthday = #{userBirthday}, sex = #{userSex} where id = #{userId}")
    void updateUser(User user);

    /**
     * 根据用户id删除用户（物理删除）
     *
     * @param id 用户id
     */
    @Delete("delete from user where id = #{id}")
    void deleteUser(Integer id);

    /**
     * 聚合函数查询总记录数
     *
     * @return 返回总记录数
     */
    @Select("select count(*) from user")
    int findTotal();

    /**
     * 根据用户名模糊查询
     *
     * @param name 用户名（带 %）
     * @return 返回符合条件的用户列表
     */
    @Select("select * from user where username like #{username}")
    @ResultMap("userMap")
    List<User> findByName(String name);
}

2.3、测试

public class UserTest {
    private InputStream inputStream;
    private SqlSession sqlSession;
    private UserDao userDao;

    @Before
    public void init() throws IOException {
        inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession();
        userDao = sqlSession.getMapper(UserDao.class);
    }

    @After
    public void destroy() throws IOException {
        sqlSession.commit();
        sqlSession.close();
        inputStream.close();
    }

    /**
     * 测试查询所有用户
     */
    @Test
    public void testFindAll() {
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
        }
    }

    /**
     * 测试根据用户id查询用户
     */
    @Test
    public void testFindById() {
        User user = userDao.findById(51);
        System.out.println(user);
    }

    /**
     * 测试新增用户
     */
    @Test
    public void testSaveUser() {
        User user = new User();
        user.setUserName("new user");
        user.setUserBirthday(new Date());
        user.setUserSex("女");
        user.setUserAddress("阿尔及利亚");
        System.out.println("保存前：" + user);

        userDao.saveUser(user);

        System.out.println("保存后：" + user);
    }

    /**
     * 测试更新用户信息
     */
    @Test
    public void testUpdateUser() {
        User user = userDao.findById(51);
        user.setUserName("updateUser");
        user.setUserAddress("刚果金");

        userDao.updateUser(user);
    }

    /**
     * 测试删除用户
     */
    @Test
    public void testDeleteUser() {
        userDao.deleteUser(50);
    }

    /**
     * 测试查询总记录数（聚合函数查询）
     */
    @Test
    public void testFindTotal() {
        int total = userDao.findTotal();
        System.out.println("共 " + total + " 条记录");
    }

    /**
     * 测试根据用户名模糊查询
     */
    @Test
    public void testFindByName() {
        List<User> users = userDao.findByName("%王%");
        for (User user : users) {
            System.out.println(user);
        }
    }
}

3、使用注解实现复杂映射关系

3.1、复杂映射关系注解

05-Mybatis注解开发（Mybatis系列终结篇）

3.2、一对一复杂映射关系

3.2.1、账户及用户实体类

  • 账户实体类
public class Account implements Serializable {
    private int id; // 账户id
    private int uid; // 用户id
    private double money;
    private User user; // 账户对应的用户对象

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "Account{" +
            "id=" + id +
            ", uid=" + uid +
            ", money=" + money +
            ", user=" + user +
            '}';
    }
}
  • 用户实体类
public class User implements Serializable {
    private int id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    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 Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

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

3.2.2、账户及用户持久层接口（注解开发）

  • 账户持久层接口
public interface AccountDao {
    /**
     * 查询所有账户，包含账户对应的用户信息（延迟加载）
     *
     * @return 返回所有账户列表
     */
    @Select("select * from account")
    @Results(
        id = "accountMap",
        value = {
            @Result(id = true, column = "id", property = "id"),
            @Result(column = "uid", property = "uid"),
            @Result(column = "money", property = "money"),
            @Result(column = "uid",
                    property = "user",
                    one = @One(select = "com.junlong.dao.UserDao.findById", fetchType = FetchType.LAZY)
                   )
        }
    )
    List<Account> findAll();
}
  • 用户持久层接口
public interface UserDao {
    /**
     * 根据用户id查询用户
     *
     * @param id 用户id
     * @return 返回用户对象
     */
    @Select("select * from user where id = #{id}")
    User findById(Integer id);
}

3.2.3、测试

public class AccountTest {
    private InputStream inputStream;
    private SqlSession sqlSession;
    private AccountDao accountDao;

    @Before
    public void init() throws IOException {
        inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession();
        accountDao = sqlSession.getMapper(AccountDao.class);
    }

    @After
    public void destroy() throws IOException {
        sqlSession.commit();
        sqlSession.close();
        inputStream.close();
    }

    /**
     * 测试查询所有账户
     */
    @Test
    public void testFindAll() {
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account.getMoney());
        }
    }
}

05-Mybatis注解开发（Mybatis系列终结篇）

如运行结果所示，注解种使用了延迟加载，没有使用户相关的信息，因此并没有执行查询用户信息的SQL。

3.3、一对多复杂映射关系

3.3.1、账户及用户实体类

  • 账户实体类
public class Account implements Serializable {
    private int id; // 账户id
    private int uid; // 用户id
    private double money;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }

    @Override
    public String toString() {
        return "Account{" +
            "id=" + id +
            ", uid=" + uid +
            ", money=" + money +
            '}';
    }
}
  • 用户实体类
public class User implements Serializable {
    private int id; // 用户id
    private String username;
    private Date birthday;
    private String sex;
    private String address;
    private List<Account> accounts;

    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 Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public List<Account> getAccounts() {
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

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

3.3.2、账户及用户持久层接口

  • 账户持久层接口
public interface AccountDao {
    /**
     * 根据用户uid查询所有账户
     *
     * @param uid 用户id
     * @return 返回该用户id的所有账户列表
     */
    @Select("select * from account where uid = #{uid}")
    List<Account> findByUid(int uid);
}
  • 用户持久层接口
public interface UserDao {
    /**
     * 查询所有用户，包含用户的所有账户信息（延迟加载）
     *
     * @return 返回所有用户列表
     */
    @Select("select * from user")
    @Results(
        id = "userMap",
        value = {
            @Result(id = true, column = "id", property = "id"),
            @Result(column = "username", property = "username"),
            @Result(column = "birthday", property = "birthday"),
            @Result(column = "sex", property = "sex"),
            @Result(column = "address", property = "address"),
            @Result(column = "id",
                    property = "accounts",
                    many = @Many(select = "com.junlong.dao.AccountDao.findByUid", fetchType = FetchType.LAZY)
                   )
        }
    )
    List<User> findAll();
}

3.3.3、测试

public class UserTest {
    private InputStream inputStream;
    private SqlSession sqlSession;
    private UserDao userDao;

    @Before
    public void init() throws IOException {
        inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession();
        userDao = sqlSession.getMapper(UserDao.class);
    }

    @After
    public void destroy() throws IOException {
        sqlSession.commit();
        sqlSession.close();
        inputStream.close();
    }

    /**
     * 测试查询所有用户（包含该用户的所有账户信息）
     */
    @Test
    public void testFindAll() {
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user.getUsername());
        }
    }
}

05-Mybatis注解开发（Mybatis系列终结篇）

如运行结果所示，注解配置了延迟加载，由于没有使用账户相关信息，因此并没有执行查询账户信息的SQL。

4、基于注解的二级缓存

4.1、主配置文件

<configuration>
  <!-- 外部配置文件 -->
  <properties resource="jdbc.properties"/>
  <!-- 开启二级缓存 -->
  <settings>
    <!-- cacheEnabled 默认取值为 true，可以省略不配 -->
    <setting name="cacheEnabled" value="true"/>
  </settings>
  <!-- 实体类别名 -->
  <typeAliases>
    <package name="com.junlong.domain"/>
  </typeAliases>
  <!-- 环境配置 -->
  <environments default="mysql">
    <environment id="mysql">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${jdbc.driver}"/>
        <property name="url" value="${jdbc.url}"/>
        <property name="username" value="${jdbc.username}"/>
        <property name="password" value="${jdbc.password}"/>
      </dataSource>
    </environment>
  </environments>
  <!-- dao路径 -->
  <mappers>
    <package name="com.junlong.dao"/>
  </mappers>
</configuration>

4.2、用户持久层接口开启二级缓存（注解开发）

// 配置二级缓存
@CacheNamespace(blocking = true)
public interface UserDao {
    /**
     * 根据用户id查询用户
     *
     * @param id 用户id
     * @return 返回用户对象
     */
    @Select("select * from user where id = #{id}")
    User findById(Integer id);
}

4.3、测试

public class UserTest {
    private InputStream inputStream;
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void init() throws IOException {
        inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @After
    public void destroy() throws IOException {
        inputStream.close();
    }

    /**
     * 测试根据用户id查询用户（二级缓存）
     *
     * 注意：只有当sqlSession被 提交 或 关闭 后，二级缓存才能生效
     */
    @Test
    public void testFindById() {
        SqlSession sqlSession1 = sqlSessionFactory.openSession();
        UserDao userDao1 = sqlSession1.getMapper(UserDao.class);
        User user1 = userDao1.findById(51);
        System.out.println(user1);
        sqlSession1.commit();
        sqlSession1.close();

        SqlSession sqlSession2 = sqlSessionFactory.openSession();
        UserDao userDao2 = sqlSession2.getMapper(UserDao.class);
        User user2 = userDao2.findById(51);
        System.out.println(user2);
        sqlSession2.commit();
        sqlSession2.close();

        System.out.println(user1 == user2);
    }
}

05-Mybatis注解开发（Mybatis系列终结篇）

如运行结果所示，两次查询只执行了一次SQL，由于二级缓存使用的是序列化存储，所以两次查询得到的对象并不是用一个。

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