Using MyBatis mapper with XML in Spring

Introduction

MyBatis is a Java framework that brings relational databases and objects together, with a native integration with Spring framework. Sometimes we want to use it to get data from a database and convert them into a designated type for our applications.

Implementation

We include mybatis and mybatis-spring packages as dependencies in pom.xml

We create applicationContext.xml and load it through web.xml

<context-param>
  <param-name>contextConfigLocation</param-name>
  <param-value>classpath:applicationContext.xml</param-value>
</context-param>

We create spring-dao.xml and load it through applicationContext.xml

<import resource="spring-dao.xml" />

We configure a session factory by specifying the class path of mapper xml files in spring-dao.xml

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="mapperLocations" value="classpath:mapper/*.xml" />
  </bean>

<bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
    <constructor-arg ref="sqlSessionFactory" />
 </bean>

To keep it simple for this demonstration, we configure the dataSource bean with jdbc url, username, passwords and other details of dataSource in the same xml file. In reality, you do not store sensitive information in your repository.

We create demoMapper.xml under the path specified in spring-dao.xml. We specify which dao file would be using this mapper in this mapper xml file by namespace.

Using a select statement as an example:

<?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.DemoDao">
	<select id="getDataByIdAndStatus" resultType="com.example.model.DemoInfo"
		parameterType="java.util.HashMap">
		select * from demo_table 
		where demo_id = #{demoId} 
		and status = 1 
		limit 1
	</select>
</mapper>

The above mapper means it is used by DemoDao with a statement named as getDataByIdAndStatus.

You may write the query using <select>, <insert>, <delete>, <update> tags for different types of statement.

In the dao file, we inject the sqlSession .

@Autowired
@Qualifier("sqlSession")
private SqlSession demoSqlSession;

We create a function to return the result to the service layer.

public DemoInfo getDataByIdAndStatus(Map<String, Object> map){
    return this.demoSqlSession.selectOne("com.example.dao.DemoDao.getDataByIdAndStatus",map);
}

The return value would be an object with a designated type.

We can get data from the database through mybatis and convert them into a designated type for further processing.

Wrapping up

We have tried to access data from a relational database by using MyBatis with XML configuration files. We also tried to convert the result into a designated type by creating a dao file.

Though, I would prefer annotation based configuration for queries to improve code readability and reduce the file size of configuration files.

References

Credits

Cover photo by Gauravdeep Singh Bansal on Unsplash