Feign 异常传递

通过Feign交互，如果服务端发送异常，feign默认会将异常包装为自定义FeignException，这样我们就不能直接获取服务端抛出的异常类型和异常描述。下面我们就来使用对象序列化的形式，将服务端的异常（Exception对象）传递到客户端。

思路

实现服务端异常传递，需要满足以下特点

服务端既能支持http直连，也能支持公共Feign请求异常对象传递

http直连：需要对异常进行包装，比如返回{"status":false,"message":"余额不足"} REST格式风格响应信息

Feign客户端：服务端将异常进行序列化，客户端将异常反序列化
服务端的异常类型在客户端不存在，需要在服务端将异常转换为RunTimeException

如服务端和客户端依赖不同的jar，会导致服务端的异常无法在客户端进行反序列化，导致客户端解析错误，最好的方式是将可能抛出的异常，在Feign 远程服务api接口声明中显示抛出，这样服务端和客户端的异常类型一致，在序列化时不会报错。

实现

运行环境
- feign：org.springframework.cloud:spring-cloud-starter-openfeign:2.2.9.RELEASE
- spring：org.springframework.boot:spring-boot-starter-parent:2.3.12.RELEASE

1. 服务端

服务端自定义异常拦截器

为了兼容Http直连，使用Feign请求时，会在请求Heard中加标签入RemoteConstant.Heard.ERROR_ENCODE=RemoteConstant.Heard.ERROR_ENCODE_SERIAL来标记是Feign请求，并且将异常序列化，如果没有配置这个Heard，或者配置的``RemoteConstant.Heard.ERROR_ENCODE是其他值，代表异常是其他的返回形式（如：{“status”:false,“message”:“余额不足”}），本例中是将异常异常信息直接输出为:异常类型：异常描述`

public class ExceptionHandle implements HandlerExceptionResolver, Ordered {

	private static final Logger LOGGER = LoggerFactory.getLogger(ExceptionHandle.class);

	private int order = Ordered.LOWEST_PRECEDENCE;


	@Override
	public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
		LOGGER.error("Request error", ex);

		String errorEncode = request.getHeader(RemoteConstant.Heard.ERROR_ENCODE);
		if (RemoteConstant.Heard.ERROR_ENCODE_SERIAL.equals(errorEncode)) {
			response.addHeader(RemoteConstant.Heard.ERROR_ENCODE, RemoteConstant.Heard.ERROR_ENCODE_SERIAL);
			response.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());
			HandlerMethod method = (HandlerMethod) handler;
			boolean normalException = normalException(ex, method);
			Exception exception = normalException ? ex : new RuntimeException(ExceptionUtils.getStackTrace(ex));
			try {
				IOUtils.write(SerializableUtil.serialize(exception), response.getOutputStream());
			} catch (IOException e) {
				//ignore
			}
			return new ModelAndView();
		}
		try {
			String errorMsg = String.format("%s : %s", ex.getClass().getName(), ex.getMessage());
			IOUtils.write(errorMsg, response.getOutputStream());
		} catch (IOException e) {
			//ignore
		}
		return new ModelAndView();
	}

	@Override
	public int getOrder() {
		return order;
	}

	public void setOrder(int order) {
		this.order = order;
	}

	/**
	 * 是否是可序列化异常
	 *
	 * @param exception
	 * @param methodHandle
	 * @return
	 */
	private boolean normalException(Exception exception, HandlerMethod methodHandle) {
		// Checked Exception
		if (!(exception instanceof RuntimeException)) {
			return true;
		}
		// 方法声明中的异常
		Method method = methodHandle.getMethod();
		for (Class<?> exceptionClass : method.getExceptionTypes()) {
			if (exception.getClass().equals(exceptionClass)) {
				return true;
			}
		}
		// 如果异常类和接口类在同一jar文件中，则直接抛出
		Class<?>[] interfaces = method.getDeclaringClass().getInterfaces();
		for (Class<?> interfaceClazz : interfaces) {
			RemoteClient remoteClient = interfaceClazz.getDeclaredAnnotation(RemoteClient.class);
			if (null == remoteClient) {
				continue;
			}
			String serviceFile = getCodeBase(interfaceClazz);
			String exceptionFile = getCodeBase(exception.getClass());
			if (serviceFile == null || exceptionFile == null || serviceFile.equals(exceptionFile)) {
				return true;
			}
		}

		// jdk exception
		String className = exception.getClass().getName();
		if (className.startsWith("java.") || className.startsWith("javax.")) {
			return true;
		}
		// customer exception
		if (className.startsWith("com.zto.zbase.common") || className.startsWith("com.zto.zbase.manager")) {
			return true;
		}
		return false;
	}


	public static String getCodeBase(Class<?> cls) {
		if (cls == null) {
			return null;
		}
		ProtectionDomain domain = cls.getProtectionDomain();
		if (domain == null) {
			return null;
		}
		CodeSource source = domain.getCodeSource();
		if (source == null) {
			return null;
		}
		URL location = source.getLocation();
		if (location == null) {
			return null;
		}
		return location.getFile();
	}
}

设置Spring异常拦截器

@Configuration
public class ExceptionInterceptor implements WebMvcConfigurer {
  @Override
	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
		ExceptionHandle exceptionHandle = new ExceptionHandle();
		exceptionHandle.setOrder(1);
		resolvers.add(exceptionHandle);
	}
}

java Exception序列化，反序列化工具 SerializableUtil.java

public class SerializableUtil {

	public static byte[] serialize(Exception exception) throws IOException {
		try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
			 ObjectOutputStream oo = new ObjectOutputStream(byteArrayOutputStream);) {
			oo.writeObject(exception);
			oo.flush();
			return byteArrayOutputStream.toByteArray();
		}
	}

	public static Exception deserialize(byte[] bytes) throws IOException, ClassNotFoundException {
		try (ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(bytes);
			 ObjectInputStream ois = new ObjectInputStream(byteArrayInputStream);) {
			return (Exception) ois.readObject();
		}
	}

}

2. 客户端

自定义Feign请求过滤器

将Feign请求Heard中，设置当前异常序列化

public class ExceptionRequestInterceptor implements RequestInterceptor {
  @Override
	public void apply(RequestTemplate template) {
		//异常序列化
		template.header(RemoteConstant.Heard.ERROR_ENCODE, RemoteConstant.Heard.ERROR_ENCODE_SERIAL);
	}
}

Feign异常解析

只会对RemoteConstant.Heard.ERROR_ENCODE=RemoteConstant.Heard.ERROR_ENCODE_SERIAL标记的异常响应反序列化

public class FeignExceptionErrorDecoder implements ErrorDecoder {

	@Override
	public Exception decode(String methodKey, Response response) {
		if (response.body() != null) {
			Collection<String> errorDecodes = response.headers().get(RemoteConstant.Heard.ERROR_ENCODE);
			if (CollectionUtils.isEmpty(errorDecodes)) {
				return errorStatus(methodKey, response);
			}
			String decodeType = errorDecodes.toArray()[0].toString();
			if (ERROR_ENCODE_SERIAL.equals(decodeType) && HttpStatus.INTERNAL_SERVER_ERROR.value() == response.status()) {
				try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
					 InputStream inputStream = response.body().asInputStream();) {
					IOUtils.copy(inputStream, byteArrayOutputStream);
					try {
						return SerializableUtil.deserialize(byteArrayOutputStream.toByteArray());
					} catch (ClassNotFoundException e) {
						return new RuntimeException(byteArrayOutputStream.toString());
					}
				} catch (IOException e) {
					return e;
				}
			}
		}
		return errorStatus(methodKey, response);
	}
  }

设置Feign配置

@Configuration
public class FeignConfiguration {
  @Bean
	public RequestInterceptor exceptionRequestInterceptor() {
		return new ExceptionRequestInterceptor();
	}
  @Bean
		public ErrorDecoder feignErrorDecoder() {
			return new FeignExceptionErrorDecoder();
		}
}

Feign 异常传递

思路

实现

1. 服务端

2. 客户端

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