简介

Feign

Feign是一个声明性web服务客户端。让编写Web服务客户端变得非常容易，只需创建一个接口并在接口上添加注解即可。让http远程调用就像接口调用一样简单。（远程http调用的工具有很多，HttpClient、OKHttp、Spring Boot中的RestTemplate等 —— 我们在 Spring Cloud alibaba 使用Nacos服务发现一文中就是使用的restTemplate的方式）

OpenFeign和Feign

Feign是由Netflix开源，但目前和ribbon一样停止更新了，所以spring 官方在feign的基础上推出了OpenFeign，目前spring Cloud基本都使用OpenFeign做http调用客户端。

入门示例

pom.xml

<?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>org.example</groupId>
    <artifactId>CloudConsumer</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <build.name>CloudConsumer</build.name>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>

        <spring.cloud.version>2021.0.4</spring.cloud.version>
        <spring.cloud.alibaba.version>2021.0.4.0</spring.cloud.alibaba.version>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.11</version>
    </parent>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring.cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>${spring.cloud.alibaba.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>

        <!-- 使用Nacos服务注册与发现 -->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>

        <!-- 使用Nacos配置管理 -->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
        </dependency>

        <!-- 使用spring-cloud-starter-loadbalancer做负载均衡 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-loadbalancer</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>

        <!-- 支持读取bootstrap配置 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-bootstrap</artifactId>
        </dependency>



        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- 添加web依赖 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>

    </dependencies>


    <profiles>
        <profile>
            <id>dev</id>
            <properties>
                <profileActive>dev</profileActive>
            </properties>
            <activation>
                <activeByDefault>true</activeByDefault>
            </activation>
        </profile>
        <profile>
            <id>test</id>
            <properties>
                <profileActive>test</profileActive>
            </properties>
        </profile>
        <profile>
            <id>pre</id>
            <properties>
                <profileActive>pre</profileActive>
            </properties>
        </profile>
        <profile>
            <id>prod</id>
            <properties>
                <profileActive>prod</profileActive>
            </properties>
        </profile>
    </profiles>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>

        <finalName>${build.name}</finalName>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
                <includes>
                    <include>mapper/**/*.xml</include>
                    <include>application.properties</include>
                    <include>application-${profileActive}.properties</include>
                    <include>bootstrap.properties</include>
                    <include>logback-spring.xml</include>
                </includes>
            </resource>
        </resources>
    </build>

</project>

Application 启动类

package com.yyoo.cloud;

import com.yyoo.cloud.conf.MyNacosLoadBalancerConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClients;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication(scanBasePackages = {"com.yyoo"})
@EnableDiscoveryClient // 开启服务注册发现功能
@EnableFeignClients  // 开启OpenFeign功能
// 更改默认的负载均衡策略
@LoadBalancerClients(defaultConfiguration = MyNacosLoadBalancerConfiguration.class)
public class Application {

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

}

MyNacosLoadBalancerConfiguration类的代码在我们的前文 Spring Cloud LoadBalancer(负载均衡) 中定义

OpenFeign客户端代码MyClient

package com.yyoo.cloud.client;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;

@FeignClient("myCloud")
public interface MyClient {

    @RequestMapping("/myCloud/conf/getName")
    String getName();

    @RequestMapping("/myCloud/conf/getCommonConf")
    String getCommonConf();
}

该调用的是我们Spring Cloud alibaba 使用Nacos配置中心一文中的Provider。所以本文中没有Provider的实现示例。

注：@FeignClient(“myCloud”)中的myCloud是我们Provider的ServiceID，@RequestMapping中的myCloud是Provider的应用上下文

注：@FeignClient注解的类上，不能使用@RequestMapping注解。（这是官网提示）

翻译过来

编写测试Controller

package com.yyoo.cloud.controller;

import com.yyoo.cloud.client.MyClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;

@RequestMapping("openFeign")
@RestController
public class MyController1 {

    @Resource
    private MyClient myClient;

    @RequestMapping("getName")
    public String getName(){
        String rs = myClient.getName();
        System.out.println("OpenFeign：" + rs);
        return rs;
    }

    @RequestMapping("getCommonConf")
    public String getCommonConf(){
        String rs = myClient.getCommonConf();
        System.out.println("OpenFeign：" + rs);
        return rs;
    }

}