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跟着大佬学SpringCloud教程 | 第三篇: 服务消费者(Feign)

一、Feign简介
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也支持可拔插式的编码器和解码器。Spring Cloud对Feign进行了封装,使其支持了Spring MVC标准注解和HttpMessageConverters。Feign可以与Eureka和Ribbon组合使用以支持负载均衡。

Feign是一个声明式的Web服务客户端,使得编写Web服务客户端变得非常容易,只需要创建一个接口,然后在上面添加注解即可。而与Ribbon不同的是,通过feign只需要定义服务绑定接口且以声明式的方法,优雅而简单的实现了服务调用。
二、创建一个feign的服务
在原先parent的基础上,新建一个spring-boot moudlel工程,取名为serice-feign,在它的pom文件引入Feign的起步依赖spring-cloud-starter-feign、Eureka的起步依赖spring-cloud-starter-netflix-eureka-client、Web的起步依赖spring-boot-starter-web,代码如下:

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.cloud</groupId>
    <artifactId>service-feign</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>service-feign</name>
    <packaging>jar</packaging>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.RELEASE</spring-cloud.version>
    </properties>

    <dependencies>
        <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-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>${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>

配置application.yml文件,代码如下:

server:
  port: 8675
spring:
  application:
    name: service-feign
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8671/eureka/

feign:
  hystrix:
    enabled: true

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

@EnableFeignClients
@EnableEurekaClient
@EnableDiscoveryClient
@SpringBootApplication
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,代码如下:

@FeignClient(value = "eurka-client-a",fallback = FeignServiceHystric.class)
public interface FeignService {
    @GetMapping(value = "/hello")
    String sayHello(@RequestParam(value = "name") String name);
}

在Web层的controller层,对外暴露一个"/hello"的API接口,通过上面定义的Feign客户端FeignService来消费服务。代码如下:

@RestController
public class FeignController {
    @Autowired
    FeignService feignService;

    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    public String sayHello(@RequestParam(value = "name") String name){
        return feignService.sayHello(name);
    }
}

多次访问http://localhost:8675/hello?name=feign,显示如下:
hellofeign ,i am from port:8672
hellofeign ,i am from port:8673
参照:https://www.fangzhipeng.com/springcloud/2018/08/03/sc-f3-feign.html

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