由之前的系列一，我们知道SqlSession是new SqlSessionTemplate(sqlSessionFactory)，我们从SqlSessionTemplate分析起。

    List-1

public class SqlSessionTemplate implements SqlSession, DisposableBean {    private final SqlSessionFactory sqlSessionFactory;    private final ExecutorType executorType;    private final SqlSession sqlSessionProxy;    private final PersistenceExceptionTranslator exceptionTranslator;    public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {        this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());    }    public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {        this(sqlSessionFactory, executorType, new MyBatisExceptionTranslator(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));    }    public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {        Assert.notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");        Assert.notNull(executorType, "Property 'executorType' is required");        this.sqlSessionFactory = sqlSessionFactory;        this.executorType = executorType;        this.exceptionTranslator = exceptionTranslator;        this.sqlSessionProxy = (SqlSession)Proxy.newProxyInstance(SqlSessionFactory.class.getClassLoader(), new Class[]{SqlSession.class}, new SqlSessionTemplate.SqlSessionInterceptor());    }...

    如上面的List-1所示，是SqlSessionTemplate的构造方法，那个executorType默认是SIMPLE，这个后面会说。

    我们要获取Mapper，底层上返还的是什么呢，如下图1所示，返回的是JDK的动态代理MapperProxy，可以去看下这个类的源码，它实现了JDK的InvocationHandler。

                                                             图1

    当我们调用Mapper的方法时，调用的就是MapperProxy的invoke方法，如下，根据调用的方法，构造一个MapperMethod，并将其缓存起来，之后执行MapperMethod的execute方法：

    List-2

public class MapperProxy
    
      implements InvocationHandler, Serializable {  private static final long serialVersionUID = -6424540398559729838L;  private final SqlSession sqlSession;  private final Class
     
       mapperInterface;  private final Map
      
        methodCache;  public MapperProxy(SqlSession sqlSession, Class
       
         mapperInterface, Map
        
          methodCache) {    this.sqlSession = sqlSession;    this.mapperInterface = mapperInterface;    this.methodCache = methodCache;  }  @Override  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {    try {      if (Object.class.equals(method.getDeclaringClass())) {        return method.invoke(this, args);      } else if (isDefaultMethod(method)) {        return invokeDefaultMethod(proxy, method, args);      }    } catch (Throwable t) {      throw ExceptionUtil.unwrapThrowable(t);    }    final MapperMethod mapperMethod = cachedMapperMethod(method);    return mapperMethod.execute(sqlSession, args);  }  private MapperMethod cachedMapperMethod(Method method) {    MapperMethod mapperMethod = methodCache.get(method);    if (mapperMethod == null) {      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());      methodCache.put(method, mapperMethod);    }    return mapperMethod;  }...
        
       
      
     
    

    MapperMethod的execute方法中传入的SqlSession是SqlSessionTemplate，execute方法里面有很多的内容，见后续的文章。