SpringCloud入门实战之三：服务消费者（Feign）

其他 2018-07-22 07:38:42 阅读次数: 0

上一篇文章，讲述了如何通过RestTemplate+Ribbon去消费服务，这篇文章主要讲述如何通过Feign去消费服务。

Feign是一个声明式的伪Http客户端，它使得写Http客户端变得更简单。使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特 性，可使用Feign 注解和JAX-RS注解。Feign支持可插拔的编码器和解码器。Feign默认集成了Ribbon，并和Eureka结合，默认实现了负载均衡的效果。

简而言之：

  • Feign 采用的是基于接口的注解
  • Feign 整合了ribbon，具有负载均衡的能力
  • 整合了Hystrix，具有熔断的能力

继续用上一节的工程， 必须先启动eureka-server 端口为8761; 之后启动service-hi 两次，端口分别为8762 、8773.

创建一个feign的服务

使用STS开发工具创建一个名称为service-feign的工程，这是第4个独立的工程

创建服务消费者服务工程service-feign自动生成的pom.xml,这一篇blog范例中勾选了Web选项，

自动会加入spring-boot-starter-web依赖，所以就不需要手动加入这web依赖，pom.xml文件的内容如下：

<?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.contoso</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>2.0.3.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>Finchley.RELEASE</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-openfeign</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>

在工程的配置文件application.yml文件，指定程序名为service-feign，端口号为8765，服务注册地址为http://localhost:8761/eureka/ ，代码如下：

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8765
spring:
  application:
    name: service-feign

在程序的启动类ServiceFeignApplication ，加上@EnableFeignClients注解开启Feign的功能：

package com.contoso;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceFeignApplication {

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

定义一个feign接口，通过@FeignClient（“服务名”），来指定调用哪个服务。比如在代码中调用了service-hi服务的“/hi”接口，代码如下：

package com.contoso;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient(value = "service-hi")
public interface SchedualServiceHi {
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam(value = "name") String name);
}

定义一个HiController控制器，对外暴露一个”/hi”的API接口，通过上面定义的Feign客户端SchedualServiceHi 来消费服务。代码如下：

package com.contoso;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HiController {

    //编译器报错，无视。 因为这个Bean是在程序启动的时候注入的，编译器感知不到，所以报错。
    @Autowired
    SchedualServiceHi schedualServiceHi;

    @GetMapping(value = "/hi")
    public String sayHi(@RequestParam String name) {
        return schedualServiceHi.sayHiFromClientOne( name );
    }
}

编译报错如下：

org.springframework.beans.factory.BeanCreationNotAllowedException: Error creating bean with name 'eurekaAutoServiceRegistration': Singleton bean creation not allowed while singletons of this factory are in destruction (Do not request a bean from a BeanFactory in a destroy method implementation!)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:208) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1089) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.ApplicationListenerMethodAdapter.getTargetBean(ApplicationListenerMethodAdapter.java:288) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.ApplicationListenerMethodAdapter.doInvoke(ApplicationListenerMethodAdapter.java:258) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.ApplicationListenerMethodAdapter.processEvent(ApplicationListenerMethodAdapter.java:180) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.ApplicationListenerMethodAdapter.onApplicationEvent(ApplicationListenerMethodAdapter.java:142) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:400) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:406) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:354) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:1000) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.close(AbstractApplicationContext.java:967) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.cloud.context.named.NamedContextFactory.destroy(NamedContextFactory.java:76) [spring-cloud-context-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:256) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroyBean(DefaultSingletonBeanRegistry.java:571) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingleton(DefaultSingletonBeanRegistry.java:543) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingleton(DefaultListableBeanFactory.java:957) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingletons(DefaultSingletonBeanRegistry.java:504) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingletons(DefaultListableBeanFactory.java:964) [spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.destroyBeans(AbstractApplicationContext.java:1041) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:1017) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext$1.run(AbstractApplicationContext.java:937) [spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]

[INFO]

启动工程顺序必须为eureka-server,service-hi(两次端口分别为8762和8763)，访问服务消费者（Feign）对外对外提供的接口地址 http://localhost:8765/hi?name=Tom 浏览器交替显示：

Hello Tom ,this message is from port:8763

Hello Tom ,this message is from port:8762

Hello Tom ,this message is from port:8763

Hello Tom ,this message is from port:8762

本篇blog源码spring-cloud-example3.zip

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