在 MyBatis 中有两种事务管理器类型，也就是 type="[JDBC|MANAGED]"：
JDBC – 这个配置直接简单使用了 JDBC 的提交和回滚设置。它依赖于从数据源得到的连接来管理事务范围。
MANAGED – 这个配置几乎没做什么。它从来不提交或回滚一个连接。而它会让容器来管理事务的整个生命周期（比如 Spring 或 JEE 应用服务器的上下文）。默认情况下它会关闭连接。然而一些容器并不希望这样，因此如果你需要从连接中停止它，将 closeConnection 属性设置为 false。例如：
<transactionManager type="MANAGED"> <property name="closeConnection" value="false"/> </transactionManager>
这两种事务管理器都不需要任何属性。
其实，JDBC 类型对应 JdbcTransactionFactory、JdbcTransaction；MANAGED 类型对应 ManagedTransactionFactory、ManagedTransaction。它们分别实现了 TransactionFactory 和 Transaction 接口。如下图：
你要自定义事务管理器需要实现 TransactionFactory 和 Transaction 接口。
（1）TransactionFactory 接口源码如下：
public interface TransactionFactory {
/**
* Sets transaction factory custom properties.
* @param props
*/
void setProperties(Properties props);
/**
* Creates a {@link Transaction} out of an existing connection.
* @param conn Existing database connection
* @return Transaction
* @since 3.1.0
*/
Transaction newTransaction(Connection conn);
/**
* Creates a {@link Transaction} out of a datasource.
* @param dataSource DataSource to take the connection from
* @param level Desired isolation level
* @param autoCommit Desired autocommit
* @return Transaction
* @since 3.1.0
*/
Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit);
}该接口定义了三个方法，一个用来设置属性，另外两个用来创建事务对象。
（2）Transaction 接口源码如下：
public interface Transaction {
/**
* Retrieve inner database connection
* @return DataBase connection
* @throws SQLException
*/
Connection getConnection() throws SQLException;
/**
* Commit inner database connection.
* @throws SQLException
*/
void commit() throws SQLException;
/**
* Rollback inner database connection.
* @throws SQLException
*/
void rollback() throws SQLException;
/**
* Close inner database connection.
* @throws SQLException
*/
void close() throws SQLException;
}该接口定义了四个方法，分别用于获取数据库连接、提交事务、回滚事务、关闭数据库连接。
当我们实现了上面两个接口，需要在别名中进行声明，例如：
<typeAliases> <!-- 声明自定义的事务管理器 --> <typeAlias alias="my_transaction" type="com.hxstrive.mybatis.transaction.demo1.MyTransactionFactory" /> </typeAliases>
然后在 <transactionManager> 标签的 type 属性中指定定义事务管理器别名，如：my_transaction
<transactionManager type="my_transaction" />
我们配置类型别名，MyBatis 是怎样发现我们自定义的事务管理器的呢？查看源码就可以知道了，如下图：
进入 resolveClass 方法，该方法将调用 resolveAlias 方法去解析别名（这里别名为 my_transaction），如下：
resolveAlias 方法中将从 TYPE_ALIASES Map中根据 key 获取别名对应的类全限定名称。如下：
（1）MyBatis 配置文件 mybatis-cfg.xml 内容如下：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="database.properties"/>
<typeAliases>
<!-- 声明自定义的事务管理器 -->
<typeAlias alias="my_transaction" type="com.hxstrive.mybatis.transaction.demo1.MyTransactionFactory" />
</typeAliases>
<environments default="MySqlDatabase" >
<environment id="MySqlDatabase" >
<!-- 使用自定义事务管理器 -->
<transactionManager type="my_transaction" />
<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>
<mappers>
<mapper resource="com/hxstrive/mybatis/transaction/demo1/UserMapper.xml" />
</mappers>
</configuration>（2）自定义事务工厂类，代码如下：
package com.hxstrive.mybatis.transaction.demo1;
import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;
public class MyTransactionFactory implements TransactionFactory {
private static final String NAME = MyTransactionFactory.class.getSimpleName();
@Override
public void setProperties(Properties props) {
System.out.println(NAME + " setProperties()");
}
@Override
public Transaction newTransaction(Connection conn) {
System.out.println(NAME + " newTransaction()");
return new MyTransaction(conn);
}
@Override
public Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit) {
System.out.println(NAME + " newTransaction()");
try {
return new MyTransaction(dataSource.getConnection());
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
}（3）自定义事务类，代码如下：
package com.hxstrive.mybatis.transaction.demo1;
import org.apache.ibatis.transaction.Transaction;
import java.sql.Connection;
import java.sql.SQLException;
public class MyTransaction implements Transaction {
private static final String NAME = MyTransaction.class.getSimpleName();
private Connection connection;
public MyTransaction(Connection connection) {
this.connection = connection;
}
@Override
public Connection getConnection() throws SQLException {
System.out.println(NAME + " getConnection()");
return this.connection;
}
@Override
public void commit() throws SQLException {
System.out.println(NAME + " commit()");
if(null != this.connection && !this.connection.getAutoCommit()) {
this.connection.commit();
}
}
@Override
public void rollback() throws SQLException {
System.out.println(NAME + " rollback()");
if(null != this.connection && !this.connection.getAutoCommit()) {
this.connection.rollback();
}
}
@Override
public void close() throws SQLException {
System.out.println(NAME + " close()");
if(null != this.connection) {
this.connection.close();
}
}
}（3）定义 Mapper 接口和配置文件
a、UserMapper.java
package com.hxstrive.mybatis.transaction.demo1;
public interface UserMapper {
/** 查询用户数 */
int getUserCount();
}b、UserMapper.xml
<?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.hxstrive.mybatis.transaction.demo1.UserMapper"> <!-- 查询用户数 --> <select id="getUserCount" resultType="integer"> select count(*) from `user` </select> </mapper>
（4）客户端代码如下：
package com.hxstrive.mybatis.transaction.demo1;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.InputStream;
public class TransactionDemo {
public static void main(String[] args) throws Exception {
String cfgName = "com/hxstrive/mybatis/transaction/demo1/mybatis-cfg.xml";
InputStream input = Resources.getResourceAsStream(cfgName);
SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlFactory = factoryBuilder.build(input);
SqlSession sqlSession = sqlFactory.openSession(true);
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
int userCount = userMapper.getUserCount();
System.out.println("用户总数=" + userCount);
sqlSession.close();
}
}运行客户端代码，输出结果如下：
MyTransactionFactory setProperties() 2020-09-13 15:59:08,269 DEBUG [org.apache.ibatis.logging.LogFactory] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter. 2020-09-13 15:59:08,316 DEBUG [org.apache.ibatis.datasource.pooled.PooledDataSource] - PooledDataSource forcefully closed/removed all connections. 2020-09-13 15:59:08,317 DEBUG [org.apache.ibatis.datasource.pooled.PooledDataSource] - PooledDataSource forcefully closed/removed all connections. 2020-09-13 15:59:08,317 DEBUG [org.apache.ibatis.datasource.pooled.PooledDataSource] - PooledDataSource forcefully closed/removed all connections. 2020-09-13 15:59:08,317 DEBUG [org.apache.ibatis.datasource.pooled.PooledDataSource] - PooledDataSource forcefully closed/removed all connections. MyTransactionFactory newTransaction() 2020-09-13 15:59:08,934 DEBUG [org.apache.ibatis.datasource.pooled.PooledDataSource] - Created connection 1555690610. MyTransaction getConnection() 2020-09-13 15:59:08,971 DEBUG [com.hxstrive.mybatis.transaction.demo1.UserMapper.getUserCount] - ooo Using Connection [com.mysql.jdbc.JDBC4Connection@5cb9f472] 2020-09-13 15:59:08,972 DEBUG [com.hxstrive.mybatis.transaction.demo1.UserMapper.getUserCount] - ==> Preparing: select count(*) from `user` 2020-09-13 15:59:09,080 DEBUG [com.hxstrive.mybatis.transaction.demo1.UserMapper.getUserCount] - ==> Parameters: 2020-09-13 15:59:09,138 DEBUG [com.hxstrive.mybatis.transaction.demo1.UserMapper.getUserCount] - <== Total: 1 用户总数=3 MyTransaction close() 2020-09-13 15:59:09,139 DEBUG [org.apache.ibatis.datasource.pooled.PooledDataSource] - Returned connection 1555690610 to pool.
