SpringCloud学习之Feign 的使用（五）

 Feign 是一个声明式的伪RPC的REST客户端，它用了基于接口的注解方式，很方便的客户端配置，刚开始使用时还不习惯，感觉是在客户端写服务端的代码，Spring Cloud 给 Feign 添加了支持Spring MVC注解，并整合Ribbon及Eureka进行支持负载均衡。

Feign的使用很简单，有以下几步：

1、添加依赖

2、启动类添加 @EnableFeignClients 注解支持

3、建立Client接口，并在接口中定义需调用的服务方法

4、使用Client接口。

具体如下首先先添加feign需要的依赖

​

1、添加 spring-cloud-starter-openfeign 依赖

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

      完整的 pom.xml

<?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>2.2.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.xu</groupId>
    <artifactId>service-consumer-feign</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>service-consumer-feign</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Hoxton.M3</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</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>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.48</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </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>

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

</project>

2、启动类添加 @EnableFeignClients 注解支持

package com.xu.serviceconsumer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceConsumerFeignApplication {

    public static void main(String[] args) {

        SpringApplication.run(ServiceConsumerFeignApplication.class, args);
    }

    @Bean
    @LoadBalanced
    RestTemplate restTemplate() {

        return new RestTemplate();
    }
}

​
3、建立Client接口，并在接口中定义需调用的服务方法

package com.xu.serviceconsumer.service;

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(name = "service-hello")
public interface UserFeignClient {

    @RequestMapping(value="/hi",method = RequestMethod.GET)
    String getName(@RequestParam String name);

}

​
    说明：>> name="service-hello"，这里的"service-hello"是注册到Eureka 中的要调用的应用名

                >> @GetMapping("/hi") 这里的“/hi”是要调用的应用里的相应的方法（这里需注意，如果service-hello服务下面的                                  访问路径是 /hi/hello ，则这里也要写"/hi/hello"）。

4、使用Client接口

​

package com.xu.serviceconsumer.controller;

import com.alibaba.fastjson.JSONObject;
import com.fasterxml.jackson.databind.util.JSONPObject;
import com.xu.serviceconsumer.service.HelloService;
import com.xu.serviceconsumer.service.UserFeignClient;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import java.util.HashMap;
import java.util.Map;

@RestController
public class HelloControler {

    private static final Logger LOGGER = LoggerFactory.getLogger(HelloControler.class);

    @Autowired
    private HelloService helloService;

    @Autowired
    private LoadBalancerClient loadBalancerClient;

    @Autowired
    private UserFeignClient userFeignClient;

    @RequestMapping(value = "/hi")
    public String hi(@RequestParam String name) {

        return helloService.hiService(name);
    }

    @RequestMapping(value = "/hello")
    public String hello(@RequestParam String name) {

        return userFeignClient.getName(name);
    }

    @RequestMapping(value = "/log-instance")
    public Object logInstance() {
        ServiceInstance serviceInstance = this.loadBalancerClient.choose("SERVICE-HELLO");
        LOGGER.info("{}:{}:{}", serviceInstance.getServiceId(),
                serviceInstance.getHost(),serviceInstance.getPort());

        JSONObject object1 = new JSONObject();
        object1.put("ServiceId",serviceInstance.getServiceId());
        object1.put("Host",serviceInstance.getHost());
        object1.put("Port",serviceInstance.getPort());
        return object1.toJSONString();
    }

}

打开浏览器，访问上面Controller中的RestApi请求http://localhost:8767/hello?name=Ronnie结果如下：

​

 
看到这里显然我们的请求响应成功了，成功调用了服务提供者的服务，本节课程到此就结束了，各位如有疑问请再下方留言，我会尽快答复，谢谢观赏！

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