Dubbo异常处理

处理Dubbo调用异常有两种方式：

封装Pojo出参，使用状态码

利用对象来返回错误吗的方式有些违背Dubbo的初衷，可以包含的信息过少，不方便定位问题

定义业务异常类

推荐方式，异常类可以包含更多信息，语义友好。

Dubbo统一异常管理

Dubbo提供了，基于SPI又提供了filter功能，此处不做过多解释，有兴趣的可以直接看Dubbo官方的SPI机制介绍。

实现方式

从ExtensionLoader类中可以发现，spi加载的目录可以看到，加载了三个目录

private static final String SERVICES_DIRECTORY = "META-INF/services/";private static final String DUBBO_DIRECTORY = "META-INF/dubbo/";private static final String DUBBO_INTERNAL_DIRECTORY = DUBBO_DIRECTORY + "internal/";

其中DUBBO_INTERNAL_DIRECTORY目录下在源码中有一份com.alibaba.dubbo.rpc.Filter文件，定义了Dubbo内部的默认过滤器，可以采用最简单的方式来处理异常：覆盖默认filter

只需要在项目里定义一个META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Filter，然后覆盖源码中的定义即可

com.alibaba.dubbo.rpc.Filter

cache=com.alibaba.dubbo.cache.filter.CacheFiltervalidation=com.alibaba.dubbo.validation.filter.ValidationFilterecho=com.alibaba.dubbo.rpc.filter.EchoFiltergeneric=com.alibaba.dubbo.rpc.filter.GenericFiltergenericimpl=com.alibaba.dubbo.rpc.filter.GenericImplFiltertoken=com.alibaba.dubbo.rpc.filter.TokenFilteraccesslog=com.alibaba.dubbo.rpc.filter.AccessLogFilteractivelimit=com.alibaba.dubbo.rpc.filter.ActiveLimitFilterclassloader=com.alibaba.dubbo.rpc.filter.ClassLoaderFiltercontext=com.alibaba.dubbo.rpc.filter.ContextFilterconsumercontext=com.alibaba.dubbo.rpc.filter.ConsumerContextFilter//此处修改为你自定义的ExceptionFilter即可exception=com.xx.xx.dubbo.ExceptionFilterexecutelimit=com.alibaba.dubbo.rpc.filter.ExecuteLimitFilterdeprecated=com.alibaba.dubbo.rpc.filter.DeprecatedFiltercompatible=com.alibaba.dubbo.rpc.filter.CompatibleFiltertimeout=com.alibaba.dubbo.rpc.filter.TimeoutFiltertrace=com.alibaba.dubbo.rpc.protocol.dubbo.filter.TraceFilterfuture=com.alibaba.dubbo.rpc.protocol.dubbo.filter.FutureFiltermonitor=com.alibaba.dubbo.monitor.support.MonitorFilter

ExceptionFilter

@Slf4j@Activate(group = Constants.PROVIDER,order = 10000)public class ExceptionFilter implements Filter {    @Override    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.                    log.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;                    }                    if(exception instanceof AppException){                        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) {                    log.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) {            log.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;        }    }}

为什么要以覆盖的方式来定义filter？

因为dubbo默认的exceptinFilter为了避免类型兼容问题，会将所有自定义异常转换为string，用RuntimeException包装后返回给consumer方，导致调用者拿不到真实的异常类，所以此处直接覆盖是最为轻松简单的办法。