MyBatis是一個輕量級的ORM框架,它簡化了對關係數據庫的使用,開發人員可以在XML或註解中編寫SQL來完成對數據庫的操作,配置與使用簡單,由於是手動寫SQL,可控性好,便於SQL調優,而且如果完全使用XML方式,SQL語句可以集中維護,可以做到與Java代碼完全隔離,也便於有DBA的團隊對SQL調優。
MyBatis的大版本號是3.x,它的前身叫iBatis,創建於2002,最後一個版本是2.3.5 GA,2012年做了重大改進,改名爲MyBatis,項目也從Apache遷移到了Google Code,目前最新版本是3.2.0,2003年2月21日發佈。
GitHub站點:http://mybatis.github.com/mybatis-3/index.html
Google站點:https://code.google.com/p/mybatis/
iBatis退休聲明:http://ibatis.apache.org/
下面通過一個例子快速體驗一下MyBatis。
準備user表,用於示例
CREATE TABLE USER (
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(20),
create_time DATETIME,
PRIMARY KEY (id)
) ENGINE = innodb DEFAULT CHARSET = utf8;
初始化數據INSERT INTO user (name, create_time) VALUES ('劉一', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('陳二', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('張三', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('李四', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('王五', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('趙六', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('孫七', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('周八', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('吳九', current_timestamp);
INSERT INTO user (name, create_time) VALUES ('鄭十', current_timestamp);
第一步:pom.xml加入以下依賴。
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.20</version>
</dependency>
<!-- mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.1.1</version>
</dependency>
第二步:編寫domain類,注意包名。public class User {
private Integer id;
private String name;
private Date createTime;
// getter, setter方法略
}
第三步:編寫dao層,使用mybatis後,這一層可以只有接口,沒有具體的類,注意包名。package fun.elricboa.demo.mapper;
public interface UserMapper {
List<User> findAll();
}
第四步:編寫dao層的mapper文件UserMapper.xml,放在fun.elricboa.demo.mapper包下。
<?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="fun.elricboa.demo.mapper.UserMapper">
<select id="findAll" resultType="User">
select * from user
</select>
</mapper>
注意:
1.mapper文件名(UserMapper.xml)要和上一步的接口名一致;
2.namespace屬性必須爲上一步接口的全類名:fun.elricboa.demo.mapper.UserMapper
第五步:編寫mybatis配置文件mybatis-config.xml,放在src/main/resources下。
<configuration>
<properties resource="database.properties"/>
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<typeAliases>
<package name="fun.elricboa.demo.domain"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${database.driverClassName}"/>
<property name="url" value="${database.url}"/>
<property name="username" value="${database.username}"/>
<property name="password" value="${database.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<package name="fun.elricboa.demo.mapper"/>
</mappers>
</configuration>
說明:
1.database.properties是數據庫配置文件,也在src/main/resources下,引入這個文件後,後面就可引用數據庫配置項。
2.typeAliases顧名思義,是類型的別名,這裏配置爲第二步domain類的包名,這樣mybatis的mapper文件中就可以直接寫類名,不必寫類的全名。
3.mappers配置第三步dao層接口類的包名,告訴mybatis接口類及mapper文件的位置。
4.mapUnderscoreToCamelCase參數用於將下劃線的命名格式轉換爲駝峯命名,如表字段名create_time,在domain類中定義爲createTime,執行sql語句後,mybatis會自動把create_time轉換爲createTime,省去了寫sql時指定別名的麻煩。
至此,代碼編寫完成,現在編寫測試用例:
public class MyBatisTest {
@Test
public void test() throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
// 通過selectList查詢
List<User> userList = sqlSession.selectList(UserMapper.class.getName() + ".findAll");
for (User user : userList) {
logger.debug(user.toString());
}
logger.debug("------------------------------------------------------------------------");
// 通過接口類查詢
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> users = mapper.findAll();
for (User user : users) {
logger.debug(user.toString());
}
} finally {
sqlSession.close();
}
}
}
以上是最簡單的查詢,下面給出條件查詢、增、刪、改的示例
對UserMapper接口增加6個方法:
List<User> findAll();
User findById(Integer id);
List<User> findByIdList(List<Integer> userIdList);
int insert(User user);
int insertList(List<User> list);
int update(User user);
int deleteById(Integer id);
}
現在實現這6個方法,對於mybatis來說,就是在xml中寫sql語句,修改UserMapper.xml:<select id="findById" parameterType="int" resultType="User">
select * from user where id = #{id}
</select>
<select id="findByIdList" parameterType="list" resultType="User">
select * from user where id in
<foreach collection="list" item="id" open="(" separator="," close=")">
#{id}
</foreach>
</select>
<insert id="insert" keyProperty="id" parameterType="User">
insert into user(
name, create_time
) values (
#{name},
<choose>
<when test="createTime != null">
#{createTime}
</when>
<otherwise>
current_timestamp
</otherwise>
</choose>
)
</insert>
<insert id="insertList" parameterType="list">
insert into user(
name, create_time
) values
<foreach collection="list" item="item" open="(" close=")" separator="),(">
#{item.name},
<choose>
<when test="item.createTime != null">
#{item.createTime}
</when>
<otherwise>
current_timestamp
</otherwise>
</choose>
</foreach>
</insert>
<update id="update" parameterType="User">
update user
<set>
<if test = "name != null">name = #{name},</if>
<if test = "createTime != null">create_time = #{createTime},</if>
</set>
where
id = #{id}
</update>
<delete id="deleteById" parameterType="int">
delete from user where id = #{id}
</delete>
注意:mybatis對於事務的auto_commit是false,對於上面的insert、update、delete實現,在測試代碼中需要手動提交事務,如:
@Test
public void testInsert() {
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = new User();
user.setName("測試");
mapper.insert(user);
// 提交事務
sqlSession.commit();
} finally {
sqlSession.close();
}
}
如果需要自動提交事務,可以在調用openSession方法時傳入參數,即sqlSessionFactory.openSession(true)