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 passedInputStream 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 resourceif (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<T> type)方法。

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

再调用MapperRegistry中的getMapper(Class<T> 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<T> mapperProxy)，创建出MapperProxy的代理对象并且返回。

UserMapper mapper = session.getMapper(UserMapper.class);public <T> T getMapper(Class<T> type, SqlSession sqlSession) {final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) 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<T> mapperProxy) {return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}public T newInstance(SqlSession sqlSession) {final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);return newInstance(mapperProxy);
}