利用Dubbo SPI中的Filter来处理异常

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http://dubbo.apache.org/zh-cn...。
我们可以通过Dubbo的Filter机制，来实现异常统一处理。

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.CacheFilter
validation=com.alibaba.dubbo.validation.filter.ValidationFilter
echo=com.alibaba.dubbo.rpc.filter.EchoFilter
generic=com.alibaba.dubbo.rpc.filter.GenericFilter
genericimpl=com.alibaba.dubbo.rpc.filter.GenericImplFilter
token=com.alibaba.dubbo.rpc.filter.TokenFilter
accesslog=com.alibaba.dubbo.rpc.filter.AccessLogFilter
activelimit=com.alibaba.dubbo.rpc.filter.ActiveLimitFilter
classloader=com.alibaba.dubbo.rpc.filter.ClassLoaderFilter
context=com.alibaba.dubbo.rpc.filter.ContextFilter
consumercontext=com.alibaba.dubbo.rpc.filter.ConsumerContextFilter

//此处修改为你自定义的ExceptionFilter即可
exception=com.xx.xx.dubbo.ExceptionFilter


executelimit=com.alibaba.dubbo.rpc.filter.ExecuteLimitFilter
deprecated=com.alibaba.dubbo.rpc.filter.DeprecatedFilter
compatible=com.alibaba.dubbo.rpc.filter.CompatibleFilter
timeout=com.alibaba.dubbo.rpc.filter.TimeoutFilter
trace=com.alibaba.dubbo.rpc.protocol.dubbo.filter.TraceFilter
future=com.alibaba.dubbo.rpc.protocol.dubbo.filter.FutureFilter
monitor=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。