Dubbo consumer如何處理provider拋出的異常：ExceptionFilter

    dubbo的consumer側通過ExceptionFilter對provider拋來的異常進行處理。

1、ExceptionFilter功能

/**
 * ExceptionInvokerFilter
 * <p>
 * Functions:
 * <ol>
 * <li>unexpected exception will be logged in ERROR level on provider side. Unexpected exception are unchecked
 * exception not declared on the interface</li>
 * <li>Wrap the exception not introduced in API package into RuntimeException. Framework will serialize the outer exception but stringnize its cause in order to avoid of possible serialization problem on client side</li>
 * </ol>
 */

    1、在provider側，unexpected exception會被以ERROR級別打印出來。unexpected exception指的是未在接口上聲明的unchecked exception；

    2、把API中沒有引入的exception包裝成RuntimeException。dubbo會序列化外層的異常，並且會嚴格保留異常的原因，以避免在客戶端出現序列化相關的問題。

2、異常的過濾和處理

2.1 異常處理邏輯

1）CheckedException直接拋出

// directly throw if it's checked exception
if (!(exception instanceof RuntimeException) && (exception instanceof Exception)) {
    return result;
}

2）顯式拋出的異常，直接拋出

// directly throw if the exception appears in the signature
try {
    Method method = invoker.getInterface().getMethod(invocation.getMethodName(), invocation.getParameterTypes());
    Class<?>[] exceptionClassses = method.getExceptionTypes();
    for (Class<?> exceptionClass : exceptionClassses) {
        if (exception.getClass().equals(exceptionClass)) {
            return result;
        }
    }
} catch (NoSuchMethodException e) {
    return result;
}

其他異常，首先在日誌中打印異常信息

// for the exception not found in method's signature, print ERROR message in server's log.
logger.error("Got unchecked and undeclared exception which called by " + RpcContext.getContext().getRemoteHost()
        + ". service: " + invoker.getInterface().getName() + ", method: " + invocation.getMethodName()
        + ", exception: " + exception.getClass().getName() + ": " + exception.getMessage(), exception);

3）異常類和接口類在同一個jar包中，直接拋出

// directly throw if exception class and interface class are in the same jar file.
String serviceFile = ReflectUtils.getCodeBase(invoker.getInterface());
String exceptionFile = ReflectUtils.getCodeBase(exception.getClass());
if (serviceFile == null || exceptionFile == null || serviceFile.equals(exceptionFile)) {
    return result;
}

4）JDK異常，直接拋出

// directly throw if it's JDK exception
String className = exception.getClass().getName();
if (className.startsWith("java.") || className.startsWith("javax.")) {
    return result;
}

5）dubbo異常，直接拋出

// directly throw if it's dubbo exception
if (exception instanceof RpcException) {
    return result;
}

6）其他異常，用RuntimeException包裹後拋給客戶端

// otherwise, wrap with RuntimeException and throw back to the client
return new RpcResult(new RuntimeException(StringUtils.toString(exception)));

2.2 源碼

    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        try {
            Result result = invoker.invoke(invocation);
            if (result.hasException() && GenericService.class != invoker.getInterface()) {
                try {
                    Throwable exception = result.getException();

                    // directly throw if it's checked exception
                    if (!(exception instanceof RuntimeException) && (exception instanceof Exception)) {
                        return result;
                    }
                    // directly throw if the exception appears in the signature
                    try {
                        Method method = invoker.getInterface().getMethod(invocation.getMethodName(), invocation.getParameterTypes());
                        Class<?>[] exceptionClassses = method.getExceptionTypes();
                        for (Class<?> exceptionClass : exceptionClassses) {
                            if (exception.getClass().equals(exceptionClass)) {
                                return result;
                            }
                        }
                    } catch (NoSuchMethodException e) {
                        return result;
                    }

                    // for the exception not found in method's signature, print ERROR message in server's log.
                    logger.error("Got unchecked and undeclared exception which called by " + RpcContext.getContext().getRemoteHost()
                            + ". service: " + invoker.getInterface().getName() + ", method: " + invocation.getMethodName()
                            + ", exception: " + exception.getClass().getName() + ": " + exception.getMessage(), exception);

                    // directly throw if exception class and interface class are in the same jar file.
                    String serviceFile = ReflectUtils.getCodeBase(invoker.getInterface());
                    String exceptionFile = ReflectUtils.getCodeBase(exception.getClass());
                    if (serviceFile == null || exceptionFile == null || serviceFile.equals(exceptionFile)) {
                        return result;
                    }
                    // directly throw if it's JDK exception
                    String className = exception.getClass().getName();
                    if (className.startsWith("java.") || className.startsWith("javax.")) {
                        return result;
                    }
                    // directly throw if it's dubbo exception
                    if (exception instanceof RpcException) {
                        return result;
                    }

                    // otherwise, wrap with RuntimeException and throw back to the client
                    return new RpcResult(new RuntimeException(StringUtils.toString(exception)));
                } catch (Throwable e) {
                    logger.warn("Fail to ExceptionFilter when called by " + RpcContext.getContext().getRemoteHost()
                            + ". service: " + invoker.getInterface().getName() + ", method: " + invocation.getMethodName()
                            + ", exception: " + e.getClass().getName() + ": " + e.getMessage(), e);
                    return result;
                }
            }
            return result;
        } catch (RuntimeException e) {
            logger.error("Got unchecked and undeclared exception which called by " + RpcContext.getContext().getRemoteHost()
                    + ". service: " + invoker.getInterface().getName() + ", method: " + invocation.getMethodName()
                    + ", exception: " + e.getClass().getName() + ": " + e.getMessage(), e);
            throw e;
        }
    }