一、概述

服务发布的过程中，实现类会被ProtocolFilterWrapper进行各种filter的封装，其中就包括ExceptionFilter。那来分析一下ExceptionFilter的代码

二、源码分析

  1. @Activate(group = CommonConstants.PROVIDER)
  2. public class ExceptionFilter extends ListenableFilter {
  4.     public ExceptionFilter() {
  5.         super.listener = new ExceptionListener();
  6.     }
  8.     @Override
  9.     public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
  10.         return invoker.invoke(invocation);
  11.     }
  13.     static class ExceptionListener implements Listener {
  15.         private Logger logger = LoggerFactory.getLogger(ExceptionListener.class);
  17.         @Override
  18.         public void onResponse(Result appResponse, Invoker<?> invoker, Invocation invocation) {
  19.             if (appResponse.hasException() && GenericService.class != invoker.getInterface()) {
  20.                 try {
  21.                     //获取方法中抛出的异常。实现方法中的异常在AbstractProxyInvoker中进行反射调用时
  22.                     //被捕捉封装起来了。这里获取具体的异常信息
  23.                     Throwable exception = appResponse.getException();
  25.                     //如果是检查类异常，直接抛出
  26.                     if (!(exception instanceof RuntimeException) && (exception instanceof Exception)) {
  27.                         return;
  28.                     }
  29.                     //如果异常是方法签名中声明的异常，则直接抛出
  30.                     try {
  31.                         Method method = invoker.getInterface().getMethod(invocation.getMethodName(), invocation.getParameterTypes());
  32.                         Class<?>[] exceptionClassses = method.getExceptionTypes();
  33.                         for (Class<?> exceptionClass : exceptionClassses) {
  34.                             if (exception.getClass().equals(exceptionClass)) {
  35.                                 return;
  36.                             }
  37.                         }
  38.                     } catch (NoSuchMethodException e) {
  39.                         return;
  40.                     }
  41.                     // for the exception not found in method's signature, print ERROR message in server's log.
  42.                     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);
  43.                     //如果异常类和接口类在同一个jar中，则直接抛出该异常
  44.                     String serviceFile = ReflectUtils.getCodeBase(invoker.getInterface());
  45.                     String exceptionFile = ReflectUtils.getCodeBase(exception.getClass());
  46.                     if (serviceFile == null || exceptionFile == null || serviceFile.equals(exceptionFile)) {
  47.                         return;
  48.                     }
  49.                     //如果是jdk的异常则直接抛出
  50.                     String className = exception.getClass().getName();
  51.                     if (className.startsWith("java.") || className.startsWith("javax.")) {
  52.                         return;
  53.                     }
  54.                     //如果是rpc的异常则直接抛出
  55.                     if (exception instanceof RpcException) {
  56.                         return;
  57.                     }
  58.                     //否则将异常包装在RuntimeException中，返回给客户端
  59.                     appResponse.setException(new RuntimeException(StringUtils.toString(exception)));
  60.                     return;
  61.                 } catch (Throwable e) {
  62.                     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);
  63.                     return;
  64.                 }
  65.             }
  66.         }
  67.         @Override
  68.         public void onError(Throwable e, Invoker<?> invoker, Invocation invocation) {
  69.             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);
  70.         }
  71.         // For test purpose
  72.         public void setLogger(Logger logger) {
  73.             this.logger = logger;
  74.         }
  75.     }
  76. }

dubbo异常处理机制设计的初衷：
这个是为了防止服务提供方抛出了消费方没有的异常，比如数据库异常类，导致消费方反序列化失败，使异常信息更奇怪，建议在业务接口上RuntimeException也声明在throws中。