mybatis的源码流程图

今天我主要来对Mybatis的底层源码进行分析，主要是以下4行代码：

InputStream is=Resources.getResourceAsStream("mybatis-config.xml");

SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(is);

SqlSession session = sqlSessionFactory.openSession();

UserMapper mapper1 = session.getMapper(UserMapper.class);

下面我们来分行介绍一下这些代码

• 获取传入的XML文件

• 

刚开始这第一行，首先调用getResourceAsStream(String resource)方法，传入mybatis-config.xml文件

public static InputStream getResourceAsStream(String resource) throws IOException {
    return getResourceAsStream(null, resource);
  }

然后该方法里面又调用了本类中的两个参数的getResuorceAsStream(ClassLoader loader，String resource)方法。

通过classLoaderWrapper.getResourceAsStream(resource, loader)方法来获取流，

再调用getResourceAsStream(resource, loader)方法，然后再调用了本类中的getResourceAsStream(String resource, ClassLoader[ ] classLoader)方法

最后判断类加载器中所读的流是否为null，如果不为null，则返回InputStream对象。

InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) {
    for (ClassLoader cl : classLoader) {
       if (null != cl) {
         // try to find the resource as passed
         InputStream returnValue = cl.getResourceAsStream(resource);
     
         // now, some class loaders want this leading "/", so we'll add it and try again if we didn't find the resource
         if (null == returnValue) {
            returnValue = cl.getResourceAsStream("/" + resource);
         }
     
         if (null != returnValue) {
            return returnValue;
         }
      }
    }
    return null;
 }

• 获取SqlSessionFactory对象

• 

再来看这个第二行：首先创建SqlSessionFactoryBuilder对象；然后调用build(InputStream inputStream)方法;

再调用本类中的build(InputStream inputStream, String environment, Properties properties)，

然后创建解析器parser，通过Xpath解析的方式去解析mybatis-config.xml 文件，保存到configuration对象中 ，

后返回DefaultSqlSessionFactory对象。

具体如下：

SqlSessionFactory sqlsessionfactor = new SqlSessionFactoryBuilder().build(is);


public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
}

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

 

• 获取SqlSession对象

• 

然后是这个第三行：首先调用openSession()方法，

再去调用本类中的openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit)方法。

接而创建事务tx，获取environment信息,通过environment构建出transactionFactory事务工厂，通过事务工厂对事物进行设置。

newExecutor()，根据Executor在全局配置中的类型，创建出对应的执行器，

最后返回 DefaultSqlSession对象。

SqlSession session = sqlsessionfactor.openSession();



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();
    }
}

 

• 获取mapper

• 

调用DefaultSqlSession中getMapper(Class type)方法。

再调用Configuration中的getMapper(Class type, SqlSession sqlSession)方法。

再调用MapperRegistry中的getMapper(Class type, SqlSession sqlSession)方法。

调用mapperProxyFactory中的newInstance(SqlSession sqlSession)方法获取一个MapperProxy对象mapperProxy。

根据mapperProxy调用newInstance(MapperProxy mapperProxy)，创建出MapperProxy的代理对象并且返回。

UserMapper mapper = session.getMapper(UserMapper.class);

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);
    }
}

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

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