springCloud(5)---服务调用方式2：feign

feign是一种声明式伪http客户端,它使得编写http客户端变得简单

使用feign，只需要创建一个接口并注解,它具有可拔插的注解特性,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和eureka结合,默认实现了负载均衡的效果。

ribbon是一个负载均衡客户端,可以很好的控制http和tcp的一些行为,feign默认集成了ribbon

feign调用服务的方式实现步骤如下：

第一步、新建maven工程,如下图：

第二步、在pom.xml中修改如下：

<?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>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>2.1.3.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.cn</groupId>
   <artifactId>eureka-feign</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>eureka-feign</name>
   <description>Demo project for Spring Boot</description>

   <properties>
      <java.version>1.8</java.version>
      <spring-cloud.version>Greenwich.SR1</spring-cloud.version>
   </properties>

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

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

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

</project>

第三步、修改application.yml代码如下：

server:
  port: 8505
spring:
  application:
    name: eureka-feign
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8501/eureka/

第四步、新建com.cn.service类,代码如下：

package com.cn.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;

/**
 * 定义一个feign接口
 * */
@FeignClient(value = "service-client1")
public interface IFeignService {
    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    String sayHelloFromClientOne(@RequestParam(value="name")String name);
}

第五步、新建包com.cn.controller,然后在该包下新建类,代码如下：

package com.cn.controller;

import com.cn.service.IFeignService;
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;
/**
 * 对外暴露一个/hi的API接口,通过feign客户端的IFeignService来消费服务
 * */
@RestController
public class HelloController {
    @Autowired
    IFeignService feignService;

    @GetMapping(value="/hi")
    public String sayHello(@RequestParam String name){
        return feignService.sayHelloFromClientOne(name);
    }
}

第六步、修改启动类如下：

package com.cn.eurekafeign;

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;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableFeignClients("com.cn.service")    //开启feign功能
@ComponentScan({"com.cn.controller"})
public class EurekaFeignApplication {

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

}

第七步、测试

启动类如下图所示

springCloud(5)---服务调用方式2：feign

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