While XML configuration remains the predominant approach in MyBatis, annotation-based development offers a streamlined alternative that is widely adopted across other frameworks in the ecosystem.

Defining Mapper Interfaces with Annotations

Annotate methods directly on the interface to specify SQL queries:

public interface UserDao {
    
    @Select("SELECT * FROM users WHERE id = #{id}")
    UserEntity findById(int id);
}

Configuring Annotation-Based Mappers

In the MyBatis core configuration file, register the mapper interface instead of an XML mapper:

<mappers>
    <mapper class="com.example.dao.UserDao"/>
</mappers>

Executing Queries

@Test
public void testQueryById() {
    SqlSession session = SqlSessionFactoryUtil.getSession();
    
    UserDao dao = session.getMapper(UserDao.class);
    UserEntity result = dao.findById(1);
    System.out.println(result);
    
    session.close();
}

Insert, Update, and Delete Operations

When working with multiple parameters of primitive types or when parameter ambiguity might occur, the @Param annotation becomes essential. For reference types, MyBatis can infer the parameter name, but explicitly using @Param improves clarity and safety.

public interface UserDao {
    
    @Insert("INSERT INTO users VALUES (#{id}, #{username}, #{password})")
    int addUser(UserEntity user);
    
    @Delete("DELETE FROM users WHERE id = 10")
    int removeUser(int id);
    
    @Update("UPDATE users SET username = #{username} WHERE id = #{id}")
    int modifyUser(UserEntity user);
    
    @Select("SELECT * FROM users")
    List<UserEntity> fetchAllUsers();
    
    @Select("SELECT * FROM users WHERE id = #{id} AND username = #{name}")
    UserEntity findByIdAndName(@Param("id") int id, @Param("name") String name);
}

Test Cases for CRUD Operations

@Test
public void testSelect() {
    SqlSession session = SqlSessionFactoryUtil.getSession();
    UserDao dao = session.getMapper(UserDao.class);
    
    UserEntity user = dao.findByIdAndName(1, "admin");
    System.out.println(user);
    
    session.close();
}

@Test
public void testInsert() {
    SqlSession session = SqlSessionFactoryUtil.getSession();
    UserDao dao = session.getMapper(UserDao.class);
    
    int rows = dao.addUser(new UserEntity(10, "testuser", "pass123"));
    if (rows > 0) {
        session.commit();
        System.out.println("Insert successful");
    }
    
    session.close();
}

@Test
public void testDelete() {
    SqlSession session = SqlSessionFactoryUtil.getSession();
    UserDao dao = session.getMapper(UserDao.class);
    
    int rows = dao.removeUser(10);
    if (rows > 0) {
        session.commit();
        System.out.println("Delete successful");
    }
    
    session.close();
}

@Test
public void testUpdate() {
    SqlSession session = SqlSessionFactoryUtil.getSession();
    UserDao dao = session.getMapper(UserDao.class);
    
    int rows = dao.modifyUser(new UserEntity(9, "updateduser", "newpass"));
    if (rows > 0) {
        session.commit();
        System.out.println("Update successful");
    }
    
    session.close();
}

Enabling Auto-Commit

The exapmles above demonstarte manual transaction commit. MyBatis supports automatic commit configuration through the openSession method:

public static SqlSession getAutoCommitSession() {
    return sqlSessionFactory.openSession(true);
}

The openSession method overload enables automatic transaction commit when passed a boolean parameter set to true.