From the previous series I, we know that SqlSession is new SqlSessionTemplate(sqlSessionFactory). We start from SqlSessionTemplate analysis.

    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());
    }
...

As shown in List-1 above, it is the construction method of SqlSessionTemplate. The executorType defaults to SIMPLE, which will be mentioned later.

To get Mapper, what is returned at the bottom? As shown in Figure 1 below, the dynamic proxy MapperProxy of JDK is returned. You can see the source code of this class, which implements the InvocationHandler of JDK.

Figure 1

When we call Mapper's method, we call MapperProxy's invoke method. As follows, according to the method we call, we construct a MapperMethod, cache it, and then execute MapperMethod's execute method:

    List-2

public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> 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;
  }
...

The SqlSession passed in from the execute method of MapperMethod is SqlSessionTemplate. There are many contents in the execute method. See the following articles.