mybatis3.4.5源码跟读

贴一段简单的mybatis使用时的测试代码

(其他配置文件省略了，如果要搭建环境推荐一个清晰的博客： https://www.cnblogs.com/xdp-gacl/p/4261895.html  )

 

package test;

import java.io.IOException;

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 org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.uu.UserMapper;

public class T {
	
	@Test
	public void test() {
		SqlSessionFactory sqlSessionFactory = getSessionFactory();
		SqlSession sqlSession = sqlSessionFactory.openSession();
		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
		userMapper.deleteOne();
		System.out.println("success");
		sqlSession.commit();
	}

	// Mybatis 通过SqlSessionFactory获取SqlSession, 然后才能通过SqlSession与数据库进行交互
	private static SqlSessionFactory getSessionFactory() {
		
		SqlSessionFactory sessionFactory = null;
		String resource = "mybatis-config.xml";
		try {
			sessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader(resource));
			//new Configuration();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return sessionFactory;
	}
}

代码入口是 SqlSessionFactoryBuilder

1、Resources.getResourceAsReader(resource) 是将配置文件解析封装成一个  java.io.Reader 对象，这个可以不用关注；

 

2、new SqlSessionFactoryBuilder 这一行代码也没有复杂的操作，只是返回一个 org.apache.ibatis.session.SqlSessionFactoryBuilder 对象；

3、构建SqlSessionFactory的逻辑在build里面

上图中实例化

org.apache.ibatis.builder.xml.XMLConfigBuilder.XMLConfigBuilder(Reader, String, Properties)时，做了具体的配置文件读取和封装；

待续。。。

 

SqlSession sqlSession = sqlSessionFactory.openSession();

最终调用的是

 

 

org.apache.ibatis.session.defaults.DefaultSqlSessionFactory.openSessionFromDataSource(ExecutorType, TransactionIsolationLevel, boolean)

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

这里创建了事务，并实例化了一个 Executor 对象，一并封装进了 DefaultSqlSession对象返回；

 

5、接下来获得Mapper

UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

最终调试调用到

 

 

org.apache.ibatis.binding.MapperRegistry.getMapper(Class, SqlSession)

 @SuppressWarnings("unchecked")
  public  T getMapper(Class type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

看到这里就大概明白了Mapper对象是通过 JDK 提供的动态代理机制实现的。