SpringCloud筆記五：Feign

時間 2019-11-13

標籤 springcloud 筆記 feign 简体版

原文原文鏈接

目錄java

什麼是Feign？

Feign的做用也是負載均衡，不過Feign是隻須要建立一個接口，而後加上註解的聲明式Web服務客戶端web

並且，Feign集成了Ribbon，默認的負載均衡方式也是輪詢。算法

有了Ribbon我還要Feign幹嗎？

上一篇文章說了，Ribbon很強大，甚至能夠自定義負載均衡的算法。那爲何還會有Feign這個負載均衡的東西呢？spring

緣由是：Ribbon對微服務的調用是這樣的編程

private static final String REST_URL_PREFIX="http://PROVIDER-DEPT";

    @Autowired
    private RestTemplate restTemplate;

Ribbon經過微服務的服務名和RestTemplate來調用，可是實際開發中會用到接口式編程，例如WebService接口，這個時候Ribbon沒辦法提供接口式的訪問，而Feign能夠。因此什麼是Feign？接口加註解的Web服務端調用的負載均衡技術。api

新建consumer-feign

咱們原有的consumer80項目，使用的是Ribbon+RestTemplate的模式，如今咱們新建一個consumer項目，起名爲consumer-feign-80，新建完成以後，Maven的pom文件裏，把consumer-80複製過來以外還須要添加Feign的引用app

<dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
            <version>1.4.6.RELEASE</version>
        </dependency>

yml文件也複製過來就能夠負載均衡

新建一個Controller，爲Feign而生處理請求，以下maven

package com.vae.springcloud.controller;

import com.vae.springcloud.entity.DeptEntity;
import com.vae.springcloud.service.DeptClientService;
import org.springframework.beans.factory.annotation.Autowired;
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.RequestBody;

import java.util.List;

public class DeptControllerFeign {

    @Autowired
    private DeptClientService service;

    @PostMapping(value = "/dept/add")
    public boolean add(@RequestBody DeptEntity deptEntity){
        return service.add(deptEntity);
    }

    @GetMapping(value = "/dept/get/{id}")
    public DeptEntity get(@PathVariable("id") Integer id){
        return service.get(id);
    }
    @GetMapping(value = "/dept/list")
    public List<DeptEntity> get() throws  Exception{
        return service.get();
    }
    @GetMapping(value = "/dept/delete/{id}")
    public boolean delete(@PathVariable("id") Integer id){
        return service.delete(id);
    }
    @GetMapping(value = "/dept/update")
    public void update(@RequestBody DeptEntity deptEntity){
        service.update(deptEntity);
    }


}

能夠看到，用到了DeptClientService這個接口，這個等下介紹，接口式編程嘛ide

主方法咱們要添加兩個和Feign有關的註解

package com.vae.springcloud;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients(basePackages = {"com.vae.springcloud"})
@ComponentScan("com.vae.springcloud")
public class ConsumerFeign80Application {

    public static void main(String[] args) {
        SpringApplication.run(ConsumerFeign80Application.class, args);
    }

}

@EnableFeignClients(basePackages = {"com.vae.springcloud"})
@ComponentScan("com.vae.springcloud")

就是這兩個註解

修改api項目

咱們的Feign是接口式加註解的負載均衡，如今上面咱們新建的子項目consumer-feign-80都加了註解了，如今開始寫接口了，在咱們的api項目裏面寫

引入Maven文件

首先，要在api項目裏引入feign的引用

<dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
            <version>1.4.6.RELEASE</version>
        </dependency>

新建feign的接口

package com.vae.springcloud.service;

import com.vae.springcloud.entity.DeptEntity;
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.RequestBody;
import java.util.List;

@FeignClient(value = "provider-dept")
public interface DeptClientService {

    @PostMapping(value = "/dept/add")
    public boolean add(@RequestBody DeptEntity deptEntity);

    @GetMapping(value = "/dept/get/{id}")
    public DeptEntity get(@PathVariable("id") Integer id);

    @GetMapping(value = "/dept/list")
    public List<DeptEntity> get();

    @GetMapping(value = "/dept/delete/{id}")
    public boolean delete(@PathVariable("id") Integer id);

    @GetMapping(value = "/dept/update")
    public void update(@RequestBody DeptEntity deptEntity);

}

啓動項目

啓動eureka集羣，再啓動provider集羣，再啓動consumer-feign-80客戶端，你能夠發現consumer是能夠訪問的，默認的仍是輪詢的方式。

可是個人項目報了一個錯，以下：

報錯

我加入了Feign的Maven引用以後就是報錯，我暫時沒法解決，致使我沒法啓動provider項目

報錯以下:

2019-04-16 12:37:18.492 ERROR 12260 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanDefinitionStoreException: Failed to process import candidates for configuration class [com.vae.springcloud.api.ApiApplication]; nested exception is java.io.FileNotFoundException: class path resource [org/springframework/boot/autoconfigure/web/ServerPropertiesAutoConfiguration.class] cannot be opened because it does not exist

Caused by: java.io.FileNotFoundException: class path resource [org/springframework/boot/autoconfigure/web/ServerPropertiesAutoConfiguration.class] cannot be opened because it does not exist

我懷疑是個人Maven配置，或者其餘某個地方配置的問題。反正我是沒法解決，網上目前查不出來緣由。

Feign啊，暫且擱置吧

若是有誰會Feign的配置這一塊，但願不吝賜教教教我......