SpringCloud学习笔记：声明式调用Feign（4）

1. Feign简介

　　Feign采用声明式API接口的风格，将Java HTTP客户端绑定到它的内部。

　　Feign的首要目标是简化Java HTTP客户端调用过程。

2.Feign客户端示例

　　

　　Feign依赖：spring-cloud-starter-feign

　　Eureka Client依赖：spring-cloud-starter-eureka

　　Web依赖：spring-cloud-starter-web

　　Spring Boot测试依赖：spring-boot-starter-test

<?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>

    <groupId>libing</groupId>
    <artifactId>eureka-feign-client</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <name>eureka-feign-client</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>libing</groupId>
        <artifactId>libing-eureka</artifactId>
        <version>1.0.0</version>
    </parent>

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

</project>

　　开启Feign Client功能：@EnableFeignClients

package libing.eurekafeignclient;

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;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class EurekaFeignClientApplication {

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

}

　　FeignConfig类加注解@Configuration，表明该类是一个配置类，并注入一个BeanName为feignRetryer的Bean。

　　组人该Bean之后，Feign在远程调用失败之后会进行重试。

package libing.eurekafeignclient.common;

import feign.Retryer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.concurrent.TimeUnit;

@Configuration
public class FeignConfig {

    @Bean
    public Retryer feignRetryer() {
        return new Retryer.Default(100, TimeUnit.SECONDS.toMillis(1), 5);
    }

}

　　DictClient接口：在接口上加上@FeignClient注解来声明一个Feign Client。其中，

　　　　value：远程调用其他服务的服务名

　　　　FeignConfig.class：Feign Client配置类

package libing.eurekafeignclient.client;

import libing.eurekafeignclient.client.model.Province;
import libing.eurekafeignclient.common.FeignConfig;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;

import java.util.List;

@FeignClient(value = "libing-dict-api", configuration = FeignConfig.class)
public interface DictClient {

    @GetMapping(value = "/dict/province")
    List<Province> getProvinceList();

}

　　DictClientService类：注入EurekaClientFeign的Bean，通过EurekaClientFeign调用。

package libing.eurekafeignclient.service;

import libing.eurekafeignclient.client.DictClient;
import libing.eurekafeignclient.client.model.Province;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class DictClientService {

    @Autowired
    DictClient dictClient;

    public List<Province> getProvinceList(){
        return dictClient.getProvinceList();
    }

}

　　DictFeignController.java

package libing.eurekafeignclient.controller;

import libing.eurekafeignclient.client.model.Province;
import libing.eurekafeignclient.service.DictClientService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping(value = "dictfeign")
public class DictFeignController {

    @Autowired
    DictClientService dictClientService;

    @GetMapping(value = "/getProvinceList")
    public List<Province> getProvinceList(){
        return dictClientService.getProvinceList();
    }

}

　　@FeignClient注解用于创建声明式API接口，该接口是RESTful风格。

　　Feign被设计成插拔式，可以注入其他组件和Feign一起使用。

　　Feign可以和Ribbon相结合进行负载均衡。

　　示例代码：libing-eureka-feignclient.zip