Mybatis源码解析之mapper接口的代理模式详解

public <T> void addMapper(Class<T> type) {
  if (type.isInterface()) {
    if (hasMapper(type)) {
      throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
    }
    boolean loadCompleted = false;
    try {
      knownMappers.put(type, new MapperProxyFactory<T>(type));
      // It's important that the type is added before the parser is run
      // otherwise the binding may automatically be attempted by the
      // mapper parser. If the type is already known, it won't try.
      MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
      parser.parse();
      loadCompleted = true;
    } finally {
      if (!loadCompleted) {
        knownMappers.remove(type);
      }
    }
  }
}

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);
  }
}

public class MapperProxyFactory<T> {
 
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();
 
  public MapperProxyFactory(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }
 
  public Class<T> getMapperInterface() {
    return mapperInterface;
  }
 
  public Map<Method, MapperMethod> getMethodCache() {
    return methodCache;
  }
 
  @SuppressWarnings("unchecked")
  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);
  }
}

@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;
}

public Object execute(SqlSession sqlSession, Object[] args) {
	 Object result;
	 switch (command.getType()) {
	   case INSERT: {
	 	Object param = method.convertArgsToSqlCommandParam(args);
	     result = rowCountResult(sqlSession.insert(command.getName(), param));
	     break;
	   }
	   case UPDATE: {
	     Object param = method.convertArgsToSqlCommandParam(args);
	     result = rowCountResult(sqlSession.update(command.getName(), param));
	     break;
	   }
	   case DELETE: {
	     Object param = method.convertArgsToSqlCommandParam(args);
	     result = rowCountResult(sqlSession.delete(command.getName(), param));
	     break;
	   }
	   case SELECT:
	     if (method.returnsVoid() && method.hasResultHandler()) {
	       executeWithResultHandler(sqlSession, args);
	       result = null;
	     } else if (method.returnsMany()) {
	       result = executeForMany(sqlSession, args);
	     } else if (method.returnsMap()) {
	       result = executeForMap(sqlSession, args);
	     } else if (method.returnsCursor()) {
	       result = executeForCursor(sqlSession, args);
	     } else {
	       Object param = method.convertArgsToSqlCommandParam(args);
	       result = sqlSession.selectOne(command.getName(), param);
	     }
	     break;
	   case FLUSH:
	     result = sqlSession.flushStatements();
	     break;
	   default:
	     throw new BindingException("Unknown execution method for: " + command.getName());
	 }
	 if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
	   throw new BindingException("Mapper method '" + command.getName() 
	       + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
	 }
	 return result;
}

private Object rowCountResult(int rowCount) {
 final Object result;
  if (method.returnsVoid()) {
    result = null;
  } else if (Integer.class.equals(method.getReturnType()) || Integer.TYPE.equals(method.getReturnType())) {
    result = rowCount;
  } else if (Long.class.equals(method.getReturnType()) || Long.TYPE.equals(method.getReturnType())) {
    result = (long)rowCount;
  } else if (Boolean.class.equals(method.getReturnType()) || Boolean.TYPE.equals(method.getReturnType())) {
    result = rowCount > 0;
  } else {
    throw new BindingException("Mapper method '" + command.getName() + "' has an unsupported return type: " + method.getReturnType());
  }
  return result;
}