使用feign作為用戶端來消費服務，提供負載均衡和斷路器支援

pom檔案如下:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.example</groupId>
	<artifactId>service-feign</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>service-feign</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.6.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
		<spring-cloud.version>Dalston.SR3</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-eureka</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-feign</artifactId>
		</dependency>
		<!--讓feign支援斷路器添加hystrix依賴-->
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-hystrix</artifactId>
		</dependency>
		<!--監控hystrix需要添加actuator依賴-->
		<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>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>


</project>
           

application.yml配置:

server:
  port: 8300
spring:
  application:
    name: service-feign
management:
  security:
    enabled: false
eureka:
  client:
    serviceUrl:
      defaultZone: http://peer1:8001/eureka/,http://peer2:8002/eureka/
feign:
  hystrix:
    enabled: true #開啟feign的hystrix支援，這個屬性idea智能補全提示不出來...
           

注意這裡如果要讓feign用戶端支援fallback的話，必須開啟feign.hystrix.enabled:true，不然不會執行熔斷保護邏輯

啟動類：

package com.example.servicefeign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@EnableCircuitBreaker //要能監控hystrix必須聲明該注解,并添加spring-boot-starter-actuator依賴
public class ServiceFeignApplication {

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

service 類:

package com.example.servicefeign.service;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

@Service //強迫症範了，加個注解讓controller中的自動注入不會出現紅線提示無法自動注入，不加也是可以運作的
@FeignClient(name = "EUREKA-CLIENT-PRODUCER", fallback = MyServiceFallback.class)
public interface MyService {

    @RequestMapping(value = "/hi", method = RequestMethod.GET)
    String test(@RequestParam("username") String username, @RequestParam("password") String password);

    @RequestMapping(value = "/hi2/{username}", method = RequestMethod.GET)
    String test2(@PathVariable("username") String username);
}
           

@FeignClient注解表名該接口是一個聲明式的feign用戶端，name是前面注冊的服務提供者的服務名(serviceId),在eureka注冊中心可以看到,GET請求如果有多個參數的話，必須用@RequestParam分别聲明，不能用一個對象來封裝所有參數後将該對象作為請求參數，這樣雖然你聲明的是GET請求，但是最終feign會以post請求發送參數，因為這個參數會放到requestBody中，隻要request body中有内容，feign就會以post方式請求了。是以如果你的服務提供發限定了隻能以GET方式請求的話，就會報錯了。

fallback開啟熔斷保護,熔斷實作由MyServiceFallback類提供，該類實作了MyService接口,同名方法實作即為對應的方法調用的fallback方法:

package com.example.servicefeign.service;

import org.springframework.stereotype.Component;

//fallback實作必須聲明為spring 的bean，不然會提示fallback實作沒有被執行個體化的錯誤
@Component
public class MyServiceFallback implements MyService {

    @Override
    public String test(String username, String password) {
        return "feign fallback:" + username + "," + password;
    }

    @Override
    public String test2(String username) {
        return "feign fallback:" + username;
    }
}
           

MyServiceFallback類必須是一個spring bean,這裡用@Component注解了該類，元件掃描會自動将該類執行個體化為一個spring bean，不然觸發fallback時會報錯提示fallback類沒有執行個體化.

最後controller類:

package com.example.servicefeign.controller;

import com.example.servicefeign.model.UserInfo;
import com.example.servicefeign.service.MyService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    @Autowired
    private MyService myService;

    @RequestMapping("/test")
    public String test(UserInfo userInfo) {
        return myService.test(userInfo.getUsername(), userInfo.getPassword());
    }

    @RequestMapping("/test2/{username}")
    public String test2(@PathVariable("username") String username) {
        return myService.test2(username);
    }
}