上一篇中我们讲了 断路器Hystrix（Ribbon） 本章讲解Feign+Hystrix已经Request请求传递，各种奇淫技巧….

- Hystrix

Hystrix支持回退概念：当 断路器 打开或运行错误时，执行默认的代码，给@FeignClient定义一个fallback属性，设置它实现回退的，还需要将您的实现类声明为Spring Bean。

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官方文档：http://cloud.spring.io/spring-cloud-static/Dalston.SR2/#spring-cloud-feign-hystrix-fallback

- 准备工作

1.启动Consul
2.创建 battcn-provider 和 battcn-consumer 如果看了上一章的，可以直接copy代码复用

- battcn-provider

- pom.xml

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<dependencies>
 <dependency>
 <groupId>org.springframework.cloud</groupId>
 <artifactId>spring-cloud-starter-consul-discovery</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-actuator</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-test</artifactId>
 <scope>test</scope>
 </dependency>
</dependencies>

- ProviderApplication.java（有变化）

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@SpringBootApplication
@EnableDiscoveryClient
@RestController
public class ProviderApplication {

 @Value("${spring.application.name}")
 String applicationName;

 public static void main(String[] args) {
 SpringApplication.run(ProviderApplication.class, args);
 }

 @GetMapping("/test1")
 public String test1() {
 return "My Name's :" + applicationName + " Email:1837307557@qq.com";
 }

 @GetMapping("/test2")
 public String test2() {
 System.out.println(1/0);
 return "hello error";
 }
}

- bootstrap.yml

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server:
 port: 8765

spring:
 application:
 name: battcn-provider
 cloud:
 consul:
 host: localhost
 port: 8500
 enabled: true
 discovery:
 enabled: true
 prefer-ip-address: true

- battcn-consumer

- pom.xml

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<dependencies>
 <dependency>
 <groupId>org.springframework.cloud</groupId>
 <artifactId>spring-cloud-starter-feign</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.cloud</groupId>
 <artifactId>spring-cloud-starter-hystrix</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-actuator</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.cloud</groupId>
 <artifactId>spring-cloud-starter-consul-discovery</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-test</artifactId>
 <scope>test</scope>
 </dependency>
</dependencies>

- ConsumerApplication

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@SpringCloudApplication
@EnableFeignClients//开启 FeignClient支持
public class ConsumerApplication {

 @Bean
 @LoadBalanced
 public RestTemplate restTemplate() {
 return new RestTemplate();
 }

 public static void main(String[] args) {
 SpringApplication.run(ConsumerApplication.class, args);
 }

}

- HiClient

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package com.battcn.client;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;

/**
 * @author Levin
 * @date 2017-08-07.
 */
@FeignClient(value = "battcn-provider",fallback = HiClient.HiClientFallback.class)
public interface HiClient {

 @GetMapping("/test1")
 String test1();

 @GetMapping("/test2")
 String test2();

 @Component
 class HiClientFallback implements HiClient{
 @Override
 public String test1() {
 return "fallback....";
 }

 @Override
 public String test2() {
 return "fallback...";
 }
 }
}

- HiController

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package com.battcn.controller;

import com.battcn.client.HiClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HiController {
 @Autowired
 HiClient hiClient;
 @GetMapping("/h1")
 public String hi() {
 return hiClient.test1();
 }
 @GetMapping("/h2")
 public String say() {
 return hiClient.test2();
 }
}

- bootstrap.yml

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server:
 port: 8766

feign:
 hystrix:
 enabled: true #开启Feign Hystrix 支持

spring:
 application:
 name: battcn-consumer
 cloud:
 consul:
 host: localhost
 port: 8500
 enabled: true
 discovery:
 enabled: true
 prefer-ip-address: true

- 测试

启动：battcn-provider

启动：battcn-consumer

访问：http://localhost:8500/ 显示如下代表服务注册成功

断路器Hystrix（Feign） 随笔 第1张查看注册中心

访问：http://localhost:8766/h1

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My Name's :battcn-provider Email:1837307557@qq.com #正确情况

访问：http://localhost:8766/h2

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fallback...  	#错误情况，阻断输出fallback...

- 解锁新姿势

- 异常处理

画图工具：https://www.processon.com/

断路器Hystrix（Feign） 随笔 第2张异常处理

如果我们FeignClient服务都是内部的，在客户端抛出异常直接往最外层抛出，就不需要在消费者通过硬编码处理了，关键代码（完整代码看GIT）…

battcn-provider 中异常处理

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@ExceptionHandler(value = Exception.class)
@ResponseBody
public ErrorResponseEntity jsonErrorHandler(Exception e, HttpServletResponse rep) throws Exception {
 if (e instanceof BattcnException) {
 BattcnException exception = (BattcnException) e;
 return exception.toErrorResponseEntity();
 }
 logger.error("服务器未知异常", e);
 rep.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());
 return new ErrorResponseEntity(HttpStatus.INTERNAL_SERVER_ERROR.value(), "服务器未知异常");
}

battcn-consumer 中异常处理

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@ExceptionHandler(value = Exception.class)
@ResponseBody
public ErrorResponseEntity jsonErrorHandler(Exception e, HttpServletResponse rep) throws Exception {
 if (e instanceof HystrixBadRequestException) {
 HystrixBadRequestException exception = (HystrixBadRequestException) e;
 rep.setStatus(HttpStatus.BAD_REQUEST.value());
 logger.info("[HystrixBadRequestException] - [" + exception.getMessage() + "]");
 JSONObject obj = JSON.parseObject(exception.getMessage());
 return new ErrorResponseEntity(obj.getInteger("customCode"), obj.getString("message"));
 }
 logger.error("服务器未知异常", e);
 rep.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());
 return new ErrorResponseEntity(HttpStatus.INTERNAL_SERVER_ERROR.value(), "服务器未知异常");
}

在Hystrix中只有，HystrixBadRequestException 是不会被计数，也不会进入阻断器，所以我们定义一个自己的错误解码器

- FeignServiceErrorDecoder

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package com.battcn.config;

import com.netflix.hystrix.exception.HystrixBadRequestException;
import feign.Response;
import feign.Util;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import java.io.IOException;

@Component
public class FeignServiceErrorDecoder implements feign.codec.ErrorDecoder {
 static Logger LOGGER = LoggerFactory.getLogger(FeignServiceErrorDecoder.class);
 @Override
 public Exception decode(String methodKey, Response response) {
 try {
 if (response.status() >= 400 && response.status() <= 499) {
 String error = Util.toString(response.body().asReader());
 return new HystrixBadRequestException(error);
 }
 } catch (IOException e) {
 LOGGER.error("[Feign解析异常] - [{}]", e);
 }
 return feign.FeignException.errorStatus(methodKey, response);
 }
}

- 测试

访问：http://localhost:8766/h1

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My Name's :battcn-provider Email:1837307557@qq.com #正确情况

访问：http://localhost:8766/h2

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{"customCode":400,"message":"请求错误"} 	#抛出异常，而不是进入阻断器

关闭battcn-provider：http://localhost:8766/h1

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fallback...  	#服务down机，阻断输出fallback...

- Request 参数传递

在开发中难免会有 服务之间 请求头传递比如Token，ID，因为我们使用的是FeignClient 的方式，那么我们无法获得HttpServletRequest的上下文，这个时候怎么办呢？通过硬编码是比较low的一种，接下来为各位看官带来简单粗暴的（也就知道这种，还有其它简单的方式欢迎交流….）

断路器Hystrix（Feign） 随笔 第3张参数传递

- FeignRequest（consumer）

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package com.battcn.config;

import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import java.util.UUID;

@Component
public class FeignRequest implements RequestInterceptor {

 final Logger LOGGER = LoggerFactory.getLogger(this.getClass().getSimpleName());

 @Override
 public void apply(RequestTemplate requestTemplate) {
 //1.模拟获取request.header参数
 String token = UUID.randomUUID().toString().replace("-","").toUpperCase();
 LOGGER.info("传递的Token - [{}]",token);
 requestTemplate.header("token",token);//模拟将Token放入在 feign.Request对象中

 }
}

- HelloController（provider）

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@Value("${spring.application.name}")
String applicationName;

@Autowired
HttpServletRequest request;

@Override
@GetMapping("/test1")
public String test1() {
 return "My Name's :" + applicationName + " Token:"+request.getHeader("token");
}

- 测试

断路器Hystrix（Feign） 随笔 第4张日志结果

结果：My Name's :battcn-provider Token:5588551D64C8478BA681A35892A03437 代表我们Token（HttpServletRequest）传递成功…

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