Dubbo學習之路（十二）：Filter—ExceptionFilter（異常處理）

上一篇主要是瞭解了Dubbo的一些常用的比較重要的原生Filter,包括consumer和provider端的。

在項目開發中呢，我們經常會遇到一些異常，有時候我們會感覺有點懵，不明白設定的自定義異常我們捕獲不道，拋出了我們不想要的異常信息，這一張我們就具體來看一下Dubbo的ExceptionFilter（異常處理）的實現。

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
                    ① 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) {
                            ② 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());
                    ③ if (serviceFile == null || exceptionFile == null || serviceFile.equals(exceptionFile)) {
                        return result;
                    }
                    // directly throw if it's JDK exception
                    String className = exception.getClass().getName();
                    ④ if (className.startsWith("java.") || className.startsWith("javax.")) {
                        return result;
                    }
                    // directly throw if it's dubbo exception
                    ⑤ if (exception instanceof RpcException) {
                        return result;
                    }

                    // otherwise, wrap with RuntimeException and throw back to the client
                    ⑥ 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;
        }
    }

我們可以看到，異常處理必然是在調用後執行的，並且是拋出了異常。

1.如果是checked異常，直接拋出

2.如果是接口上申明的異常，直接拋出

3.如果拋出的異常類，跟當前接口在同一個Jar包裏面，直接拋出

4.如果是JDK自帶的異常，直接拋出

5.如果是RpcException，直接拋出

6.如果不在前面5中情況裏的異常，封裝成RuntimeException拋出