声明式服务调用Feign

1.背景

当我们通过RestTemplate调用其它服务的API时，所需要的参数须在请求的URL中进行拼接，如果参数少的话或许我们还可以忍受，一旦有多个参数的话，这时拼接请求字符串就会效率低下，并且显得好傻。

那么有没有更好的解决方案呢？答案是确定的有，Netflix已经为我们提供了一个框架：Feign。

2.Feign概述

Feign是Spring Cloud提供的声明式、模板化的HTTP客户端， 它使得调用远程服务就像调用本地服务一样简单，只需要创建一个接口并添加一个注解即可。

Spring Cloud集成Feign并对其进行了增强，使Feign支持了Spring MVC注解；Feign默认集成了Ribbon，所以Fegin默认就实现了负载均衡的效果。

3.Feign入门

3.1.创建服务提供者

• 创建工程

• 拷贝ribbon_provider_1
  

• application.yml

server:
  port: 9090
spring:
  cloud:
    nacos:
      discovery:
        server-addr: 192.168.209.129:8848
  application:
    name: feign-provider

3.2.创建feign接口

• 创建工程
  
• pom.xml

<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">
    <parent>
        <artifactId>springcloud_parentartifactId>
        <groupId>com.bjpowernodegroupId>
        <version>1.0-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>

    <artifactId>feign_interfaceartifactId>

    <dependencies>
        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-openfeignartifactId>
        dependency>
        <dependency>
            <groupId>com.bjpowernodegroupId>
            <artifactId>springcloud_commonartifactId>
            <version>1.0-SNAPSHOTversion>
        dependency>
    dependencies>
project>

• feign

package com.bjpowernode.feign;

import com.bjpowernode.fallback.UserFeignFallback;
import com.bjpowernode.pojo.User;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
@FeignClient(value="sentinel-provider",fallbackFactory = UserFeignFallback.class)
@RequestMapping(value = "/provider")
public interface UserFeign {
    @RequestMapping(value = "/getUserById/{id}")
    public User getUserById(@PathVariable(value="id") Integer id);
}

3.3.创建服务消费者

• 创建工程
  • 拷贝ribbon_consumer
    
• pom.xml

<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">
    <parent>
        <artifactId>springcloud_parentartifactId>
        <groupId>com.bjpowernodegroupId>
        <version>1.0-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>

    <artifactId>ribbon_consumerartifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
        <dependency>
            <groupId>com.bjpowernodegroupId>
            <artifactId>springcloud_commonartifactId>
            <version>1.0-SNAPSHOTversion>
        dependency>
        <dependency>
            <groupId>com.alibaba.cloudgroupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discoveryartifactId>
        dependency>
        
        <dependency>
            <groupId>com.bjpowernodegroupId>
            <artifactId>feign_interfaceartifactId>
            <version>1.0-SNAPSHOTversion>
        dependency>
    dependencies>
project>

• application.yml

server:
  port: 80
spring:
  cloud:
    nacos:
      discovery:
        server-addr: 192.168.209.129:8848
  application:
    name: feign-consumer

• Controller

@RestController
@RequestMapping(value = "/consumer")
public class ConsumerController {

    @Autowired
    private UserFeign userFeign;

    @RequestMapping(value = "/getUserById/{id}")
    public User getUserById(@PathVariable Integer id) {
        return userFeign.getUserById(id);
    }
}

• app

package com.bjpowernode;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableDiscoveryClient
//@EnableFeignClients(basePackages = "com.bjpowernode.feign")
@EnableFeignClients//开启feign接口扫描
public class ConsumerApp {

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

3.4.测试