转载自
http://blog.csdn.net/forezp/article/details/69808079

上一篇文章，讲述了通过restTemplate+ribbon去消费服务，这篇文章主要讲述通过feign去消费服务。

一、Feign简介

Feign是一个声明式的web服务客户端，它使得写web服务变得更简单。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，包括Feign 注解和JAX-RS注解。Feign同时支持可插拔的编码器和解码器。spring cloud对Spring mvc添加了支持，同时在spring web中次用相同的HttpMessageConverter。当我们使用feign的时候，spring cloud 整和了Ribbon和eureka去提供负载均衡。

简而言之：

• feign采用的是接口加注解
• feign 整合了ribbon

二、准备工作

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

三、创建一个feign的服务

创建一个spring-boot工程，取名为：serice-feign,它的pom文件为：

<?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.forezp</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>1.5.2.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>
    </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>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>Dalston.RC1</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>

    <repositories>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>


</project>

向服务注册中心注册它自己，这时service-feign既是服务提供者，也是服务消费者,配置文件application.yml

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

在程序的入口类，需要通过注解@EnableFeignClients来开启feign:

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceFeignApplication {

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

定义一个feign接口类,通过@ FeignClient（“服务名”），来指定调用哪个服务：

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

在web层的controllrt:

@RestController
public class HiController {

    @Autowired
    SchedualServiceHi schedualServiceHi;
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    public String sayHi(@RequestParam String name){
        return schedualServiceHi.sayHiFromClientOne(name);
    }
}

访问http://localhost:8765/hi?name=forezp,浏览器交替显示：

hi forezp,i am from port:8762

hi forezp,i am from port:8763

四、更改feign的配置

在声明feignclient的时候，不仅要指定服务名，同时需要制定服务配置类：

@FeignClient(name = "stores", configuration = FooConfiguration.class)
public interface StoreClient {
    //..
}

重写配置，需要加@Configuration注解，并重写下面的两个bean,栗子：

@Configuration
public class FooConfiguration {
    @Bean
    public Contract feignContractg() {
        return new feign.Contract.Default();
    }

    @Bean
    public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
        return new BasicAuthRequestInterceptor("user", "password");
    }
}