简介

声明式服务调用Feign简单介绍下；

Feign是一个声明式的Web Service客户端，它使得编写Web Serivce客户端变得更加简单。我们只需要使用Feign来创建一个接口并用注解来配置它既可完成。它具备可插拔的注解支持，包括Feign注解和JAX-RS注解。Feign也支持可插拔的编码器和解码器。Spring Cloud为Feign增加了对Spring MVC注解的支持，还整合了Ribbon和Eureka来提供均衡负载的HTTP客户端实现。

这段话看起来比较懵逼，这里说下实际使用，前面Ribbon调用服务提供者，我们通过restTemplate调用，缺点是，多个地方调用，同一个请求要写多次，不方便统一维护，这时候Feign来了，就直接把请求统一搞一个service作为FeignClient，然后其他调用Controller需要用到的，直接注入service，直接调用service方法即可；同时Feign整合了Ribbon和Eureka，所以要配置负载均衡的话，直接配置Ribbon即可，无其他特殊地方；当然Fiegn也整合了服务容错保护，断路器Hystrix，后面再说。

应用

1、在common项目里建一个service（实际项目肯定是多个service）作为Feign客户端，用Feign客户端来调用服务器提供者，当然可以配置负载均衡；Feign客户端定义的目的，就是为了方便给其他项目调用；

修改 microservice-common

pom.xml引入Feign依赖：

 <!--引入Feign依赖-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>

我们定义了 FeignClient，同时指定了调用的服务名称MICROSERVICE-STUDENT

common项目修改后，maven clean下 然后install下；

建StudentClientService接口；

package com.javaxl.microservicecommon.service;

import com.javaxl.microservicecommon.entity.Student;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;

import java.util.List;

/**
 * Student Feign接口客户端
 * @author Administrator
 *
 */
@FeignClient(value="MICROSERVICE-STUDENT")
public interface StudentClientService {
 
    /**
     * 根据id查询学生信息
     * @param id
     * @return
     */
    @GetMapping(value="/student/get/{id}")
    public Student get(@PathVariable("id") Integer id);
     
    /**
     * 查询学生信息
     * @return
     */
    @GetMapping(value="/student/list")
    public List<Student> list();
     
    /**
     * 添加或者修改学生信息
     * @param student
     * @return
     */
    @PostMapping(value="/student/save")
    public boolean save(Student student);
     
    /**
     * 根据id删除学生信息
     * @return
     */
    @GetMapping(value="/student/delete/{id}")
    public boolean delete(@PathVariable("id") Integer id);

    @RequestMapping("/student/ribbon")
    public String ribbon();
}

2、新建一个Feign消费者项目；

参考microservice-student-consumer-80建一个microservice-student-consumer-feign-80

代码都复制一份，包括pom.xml

Pom依赖

<properties>
    <java.version>1.8</java.version>
</properties>
<dependencies>
    <dependency>
        <groupId>com.javaxl</groupId>
        <artifactId>microservice-common</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>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
    </dependency>
    <!--  修改后立即生效，热部署  -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>springloaded</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
    </dependency>
    <dependency>
        <groupId>com.javaxl</groupId>
        <artifactId>microservice-common</artifactId>
        <version>1.0-SNAPSHOT</version>
        <scope>compile</scope>
    </dependency>

    <!--ribbon相关依赖-->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-eureka</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-ribbon</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-config</artifactId>
    </dependency>

    <!--引入Feign依赖-->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-feign</artifactId>
    </dependency>
</dependencies>

SpringCloudConfig.java

package com.javaxl.microservicestudentconsumerfeign80.config;

import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RetryRule;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

@Configuration
public class SpringCloudConfig {

    @LoadBalanced  // 引入ribbon负载均衡
    @Bean
    public RestTemplate getRestTemplate() {
        return new RestTemplate();
    }

    /**
     * 自定义调用规则（服务提供者掉线后不再调用，解决轮询问题）
     * @return
     */
    @Bean
    public IRule myRule(){
        return new RetryRule();
//        return new RandomRule();
    }
}

Yml文件

server:
  port: 80
  context-path: /
eureka:
  client:
    service-url:
      defaultZone: http://eureka2001.javaxl.com:2001/eureka/,http://eureka2002.javaxl.com:2002/eureka/,http://eureka2003.javaxl.com:2003/eureka/
    register-with-eureka: false

3、修改启动类名称，和加注解

启动类名称改下，改成StudentConsumerFeignApplication_80，同时加个注解@EnableFeignClients

支持下Feign；

@EnableEurekaClient
@EnableFeignClients(value = "com.javaxl.*.*")
@SpringBootApplication(exclude={DataSourceAutoConfiguration.class, HibernateJpaAutoConfiguration.class})
public class MicroserviceStudentConsumerFeign80Application {

    public static void main(String[] args) {
        SpringApplication.run(MicroserviceStudentConsumerFeign80Application.class, args);
    }

}

4、修改controller

StudentConsumerController.java

package com.javaxl.microservicestudentconsumerfeign80.controller;

import com.javaxl.microservicecommon.entity.Student;
import com.javaxl.microservicecommon.service.StudentClientService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;

import java.util.List;

@RestController
@RequestMapping("/student")
public class StudentConsumerController {

    @Autowired
    private StudentClientService studentClientService;

    @Autowired
    private RestTemplate restTemplate;

    @PostMapping(value = "/save")
    private boolean save(Student student) {
        return studentClientService.save(student);
    }

    @GetMapping(value = "/list")
    public List<Student> list() {
        return studentClientService.list();
    }

    @GetMapping(value = "/get/{id}")
    public Student get(@PathVariable("id") Integer id) {
        return studentClientService.get(id);
    }

    @GetMapping(value = "/delete/{id}")
    public boolean delete(@PathVariable("id") Integer id) {
        try {
            studentClientService.delete(id);
            return true;
        } catch (Exception e) {
            return false;
        }
    }

    @RequestMapping("/ribbon")
    public String ribbon(){
        return studentClientService.ribbon();
    }
}

因为现在用Fiegn，所以把restTemplate去掉，改成注入service，调用service方法来实现服务的调用；

5、测试负载均衡；

SpringCloudConfig类的myRule，大伙自行修改测试即可；

出现这个结果就ok了。。。。。。