feign源代码解析

pom配置

本文介绍的feign版本为2.0.1.RELEASE， pom设置如下所示：

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
    <version>2.0.1.RELEASE</version>
</dependency>

同时会依赖引入feign-core-9.5.1.jar，相关的源代码就在这里。

源代码分析

InvocationHandlerFactory 控制反转调用入口在feign.InvocationHandlerFactory.class中

static final class Default implements InvocationHandlerFactory { @Override public InvocationHandler create(Target target, Map<Method, MethodHandler> dispatch) { return new ReflectiveFeign.FeignInvocationHandler(target, dispatch); } }
ReflectiveFeign

feign调用invoke入口(cglib)，这里equals()、hashCode()和toString()直接调本地方法就行了，不需要往下执行。

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
	if ("equals".equals(method.getName())) {
		try {
			Object otherHandler = args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
			return equals(otherHandler);
		} catch (IllegalArgumentException e) {
			return false;
		}
	} else if ("hashCode".equals(method.getName())) {
		return hashCode();
	} else if ("toString".equals(method.getName())) {
		return toString();
	}
	return dispatch.get(method).invoke(args);
}

SynchronousMethodHandler

上文dispatch.get(method).invoke(args);调用函数如下：

@Override public Object invoke(Object[] argv) throws Throwable { RequestTemplate template = buildTemplateFromArgs.create(argv); Retryer retryer = this.retryer.clone(); while (true) { try { return executeAndDecode(template); } catch (RetryableException e) { retryer.continueOrPropagate(e); if (logLevel != Logger.Level.NONE) { logger.logRetry(metadata.configKey(), logLevel); } continue; } } }

这里做了几个事情： - RequestTemplate: 组装请求参数 - executeAndDecode: 发送请求与回应数据解码

RequestTemplate 参数组装过程

最终创建的request，包括如下的内容：method，url，body，charset。

public Request request() {
    Map<String, Collection<String>> safeCopy = new LinkedHashMap<String, Collection<String>>();
    safeCopy.putAll(headers);
    return Request.create(
        method, url + queryLine(),
        Collections.unmodifiableMap(safeCopy),
        body, charset
    );
  }

executeAndDecode 发送请求与响应处理

  Object executeAndDecode(RequestTemplate template) throws Throwable {
      //创建request
  		Request request = targetRequest(template);

if (logLevel != Logger.Level.NONE) { logger.logRequest(metadata.configKey(), logLevel, request); } Response response; long start = System.nanoTime(); try {

          //通过client发送请求
  			response = client.execute(request, options);
  			// ensure the request is set. TODO: remove in Feign 10
  			response.toBuilder().request(request).build();
  		} catch (IOException e) {
  			if (logLevel != Logger.Level.NONE) {
  				logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));
  			}
  			throw errorExecuting(request, e);
  		}
  		long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);

boolean shouldClose = true; try { if (logLevel != Logger.Level.NONE) { response = logger.logAndRebufferResponse(metadata.configKey(), logLevel, response, elapsedTime); // ensure the request is set. TODO: remove in Feign 10 response.toBuilder().request(request).build(); } if (Response.class == metadata.returnType()) { if (response.body() == null) { return response; } if (response.body().length() == null || response.body().length() > MAX_RESPONSE_BUFFER_SIZE) { shouldClose = false; return response; } // Ensure the response body is disconnected byte[] bodyData = Util.toByteArray(response.body().asInputStream()); return response.toBuilder().body(bodyData).build(); }

          //http相应码是200～300区间以及404的，采用正确的decoder
  			if (response.status() >= 200 && response.status() < 300) {
  				if (void.class == metadata.returnType()) {
  					return null;
  				} else {
  					return decode(response);
  				}
  			} else if (decode404 && response.status() == 404 && void.class != metadata.returnType()) {
  				return decode(response);
  			} else {
              //使用errorDecoder
  				throw errorDecoder.decode(metadata.configKey(), response);
  			}
  		} catch (IOException e) {
  			if (logLevel != Logger.Level.NONE) {
  				logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime);
  			}
  			throw errorReading(request, response, e);
  		} finally {
  			if (shouldClose) {
  				ensureClosed(response.body());
  			}
  		}
  	}    

这里通过httpclient发送请求
请求回来的处理，根据response.status()来采取不同的策略，这里需要关注的是errorDecoder。

关于errorDecoder 与异常统一处理

在服务提供者与服务消费者之间，如果需要把提供者发生的异常传递给消费者，提供者可以通过@ControllerAdvice捕捉异常，返回500. 如下所示：

@ControllerAdvice
public class ProviderControllerAdviceHandler {

	private static final Logger log = LoggerFactory.getLogger(ProviderControllerAdviceHandler.class.getSimpleName());

	@ExceptionHandler(Throwable.class)
	@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
	@ResponseBody
	public BizException processProviderException(HttpServletRequest request, HttpServletResponse response, Throwable e) throws ServletException, IOException {
		try{
			log.error("服务提供者发生异常---------------------------");
			log.error("getRequestURI: "+request.getRequestURI());
			log.error("getRemoteAddr: "+request.getRemoteAddr());
			log.error("getQueryString: "+request.getQueryString());
			log.error("异常信息："+e.getClass()+","+e.getMessage());
			log.error(e.getMessage(), e);
			
			//如果是代码手动抛出的异常,则类型为bizException
			if(e instanceof BizException){
				log.error("异常信息："+((BizException)e).getErrorCode()+","+((BizException)e).getErrorMsg());
				return (BizException)e;
			}
		}catch(Exception ee){
			ee.printStackTrace();
		}
		//其他异常转化为bizException
		return new BusinessException(new GlobalResponseCode(GlobalResponseCode.SYS_PASS_EXCEPTION.getCode(),e.getMessage()));
	}
}

@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR) 是重点

在消费者端自定义feign的errorDecoder，如下所示：

public class FeignErrorDecoder implements ErrorDecoder{

	public Exception decode(String methodKey, Response response) {
		try {
			System.out.println(response.headers().toString());
			String body = IOUtils.toString(response.body().asInputStream());
			System.out.println(body);
			JSONObject m = JSONObject.parseObject(body);
			System.out.println(m.get("code"));
			System.out.println(m.get("msg"));
			return new BizException(m.getInteger("code"),m.getString("msg"));
		} catch (IOException e) {
			e.printStackTrace();
		}
		return new Default().decode(methodKey, response);
	}
}

消费者统一异常处理流程如下：

@ControllerAdvice public class GlobalExceptionHandler { private static final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class); @ExceptionHandler(Throwable.class) @ResponseStatus(HttpStatus.OK) @ResponseBody public ResBody processConsumerException(HttpServletRequest request, HttpServletResponse response,Throwable e) throws ServletException, IOException { log.error(e.getMessage(), e); log.error(“服务消费者捕捉到了异常—————————”); log.error(“getRequestURI: “+request.getRequestURI()); log.error(“getRemoteAddr: “+request.getRemoteAddr()); log.error(“getQueryString: “+request.getQueryString()); log.error(“异常信息：”+e.getClass()+”,”+e.getMessage()); ResBody resBody = null; //如果是代码手动抛出的异常,则类型为bizException if (e instanceof BizException) { log.error(“异常信息：”+((BizException)e).getErrorCode()+”,”+((BizException)e).getErrorMsg()); resBody= ResBody.buildFailResBody(new GlobalResponseCode(((BizException) e).getErrorCode(), ((BizException) e).getErrorMsg())); } else{ //其他异常返回系统程序异常错误 resBody = ResBody.buildFailResBody(); } return resBody;

}
}

在异常处理中，还需要根据同步请求还是异步请求，采取不同的策略。

feign配置

#连接超时时间
ribbon.ConnectTimeout=30000
#读取超时时间
ribbon.ReadTimeout=60000

写在最后的话

这里只是大概梳理了一下feign对网络请求的流程，太细节的内容，我也没有太深入，主要还是点到即止，先解决问题再说。

在实现异常统一处理流程的时候，只是看了相关的文档和博客，但是遇到的问题，根本就无从解决，最后还是回归代码，代码里面已经告诉了你一切内容。feign的流程代码也不是很复杂，相信大家都可以看得明白。

其他内容

spring-cloud-openfien-core-2.0.1.RELEASE.jar FeignClientsRegistrar.registerFeignClients()
spring-boot-autoconfigure-2.0.4.RELEASE.jar IntegrationAutoConfigurationScanRegistrar.registerBeanDefinitions()

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