MyBatis with Spring

Quick note about MyBatis with Spring. It’s a summary from official site mybatis-spring. Code demo: A simple SpingMVC + Mybatis Helloworld

Requirement

Additional jar org.mybatis.mybatis-spring is needed

Data Source

Here, any kind of DataSource is allowed. For example, org.springframework.jdbc.jar:

<!-- In Resources folder, create jdbc.properties with following content -->
<!-- jdbc.driver=com.mysql.jdbc.Driver -->
<!-- jdbc.url=jdbc:mysql://localhost:3306/db_name -->
<!-- jdbc.username=root -->
<!-- jdbc.password=password -->
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="location" value="classpath:jdbc.properties"/>
</bean>

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="${jdbc.driver}"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>

I got CannotGetJdbcConnectionException when coded my SpingMVC + Mybatis Helloworld example. The solution is to add ?useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT. So set explicitly unicode and timezone.

Setup SqlSessionFactory

In previous note MyBatis Basic, we get SqlSessionFactory by SqlSessionFactoryBuilder:

String resource = "path/to/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

But in MyBatis-Spring xml, bean SqlSessionFactory is created by SqlSessionFactoryBean:

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" /> <!-- Obliged -->
    <!-- Indicate location of mapper files where exists mysql statements -->
    <property name="mapperLocations" value="classpath*:/mybatis/*Mapper.xml"/>
    <!-- Indicate mybatis config files where exists typeAliases, settings, etc -->
    <property name="configLocation" value="classpath:/mybatis/mybatis-config.xml"/>
</bean>

<!-- In java code, it does the following step to create SqlSessionFactory
SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
SqlSessionFactory sessionFactory = factoryBean.getObject();
-->

Define mappers

Two ways to define:

Annotation based
XML based

When using xml based:

Tell SqlSessionFactoryBean where to find it by mapperLocations.
Mapper namespace must be full package path to mapper interface.
id must be the same as function name in mapper interface, also the resultType, paramType, etc.

The following example mixed both of xml and annotation.

<?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">
<!-- namespace must indicate mapper interface full package path -->
<mapper namespace="com.dong.web.mapper.UserMapper">

    <select id="getRowCount" resultType="int">
        select count(*) from tb_user
    </select>

</mapper>

public interface UserMapper {

    int getRowCount();

    @Select("select * from tb_user")
    List<User> getAllUsers();

}

SqlSession

In previous note MyBatis Basic, we get SqlSession from SqlSessionFactory and do transaction manually like following.

SqlSession session = sqlSessionFactory.openSession();

try {
  	...
  	session.commit();
} catch(Exception e) {
	e.printStackTrace();
	session.rollback(); 
} finally {
	session.close();
}

But in mybatis-spring, beans will be injected with a thread safe SqlSession that automatically commits, rollbacks and closes the session based on Spring’s transaction configuration.

We have two ways to get sesion in DAOs:

SqlSessionTemplate
SqlSessionDaoSupport

But I prefer to use MapperScannerConfigurer or MapperFactoryBean directly to avoid coding DAOs manually. MapperScannerConfigurer could even automatically scan mapper interfaces. It’s the beat choice!

Transaction

So first, in mybatis-spring, just need to enable Spring transaction processing:

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
</bean>
<tx:annotation-driven transaction-manager="transactionManager"/>

Then add @Transactional annotation on service layer.

SqlSessionTemplate

SqlSessionTemplate implements SqlSession. It is thread safe and can be shared by multiple DAOs or mappers. It is used to:

Ensure that SqlSession used is the one associated with the current Spring transaction when call SQL method.
Manage session life-cycle, including closing, committing or rolling back the session as necessary.
Translate MyBatis exceptions into Spring DataAccessExceptions.

So the idea here is to create a bean of SqlSessionTemplate and inject it in DAO layer:

<!-- Create a SqlSession bean -->
<bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
    <constructor-arg index="0" ref="sqlSessionFactory" />
</bean>

<!-- Inject it in DAO layer -->
<bean id="userDAO" class="com.dong.web.dao.UserDaoImpl">
    <property name="sqlSession" ref="sqlSession" />
</bean>

DAO class with injected sqlSession:

public class UserDaoImpl implements UserDao {

    private SqlSession sqlSession;

    public void setSqlSession(SqlSession sqlSession) {
        this.sqlSession = sqlSession;
    }

    public List<User> getAllUsers() {
        return sqlSession.select("com.dong.web.mapper.UserMapper.getAllUsers");
    }
}

Batch Processing

To enable batch feature:

<bean id="sqlSession" class="com.dong.web.dao.UserServiceImpl">
    <constructor-arg index="0" ref="sqlSessionFactory" />
    <constructor-arg index="1" value="BATCH" />
</bean>

Now all SQL statements will be batched:

public void insertUsers(User[] users) {
    for (User user : users) {
        sqlSession.insert("org.dong.web.mapper.UserMapper.insertUser", user);
    }
}

SqlSessionDaoSupport

It is an abstract support class that provides SqlSession. We could call getSqlSession() by extending SqlSessionDaoSupport to get SqlSession:

public class UserDaoImpl extends SqlSessionDaoSupport implements UserDao {

    public User getUser(String userId) {
        return (User) getSqlSession().selectOne("com.dong.web.mapper.UserMapper.getUser", userId);
    }
    
}

MapperFactoryBean

It is used to avoid coding manually DAOs by SqlSessionDaoSupport or SqlSessionTemplate, so no DAOs here in java code! It handles creating an SqlSession as well as closing it. If there is a Spring transaction in progress, the session will also be committed or rolled back when the transaction completes.

<!-- Create a MapperFactoryBean for UserMapper interface -->
<bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
    <property name="mapperInterface" value="com.dong.web.mapper.UserMapper" />
</bean>

<!-- Inject mapper in service layer -->
<bean id="userService" class="com.dong.web.service.UserServiceImpl">
    <property name="userMapper" ref="userMapper" />
</bean>

public class UserServiceImpl implements UserService {

  private UserMapper userMapper;

  public void setUserMapper(UserMapper userMapper) {
    this.userMapper = userMapper;
  }

  public List<User> getAllUsers() {
    return this.userMapper.getAllUsers();
  }
}

MapperScannerConfigurer

With MapperFactoryBean, we need to declare a bean for each mapper interface. So better to use MapperScannerConfigurer to automatically scan to find mapper interfaces and register each of them as a MapperFactoryBean.

<!-- Scan all the interfaces under mapper/ -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
   <property name="basePackage" value="com.dong.web.mapper" />
</bean>

IDE will mention Could not autowired, it’s because each MapperFactoryBean is created by MapperScannerConfigurer, IDE could not find yet an existing implementation, D’ont worry. (To check, at least, when I tried my helloworld, it works fine even with this error check)