1. 定义

Feign是Netflix开发的声明式、模板化的HTTP客户端，其灵感来自Retrofit、JAXRS-2.0以及WebSocket。Feign 可帮助我们更加便捷、优雅地调用HTTP API。在Spring Cloud中，使用Feign非常简单——只需创建接口，并在接口上添加注解即可。 Feign支持多种注解，例如Feign自带的注解或者JAX-RS注解等。Spring Cloud对Feign进行了增强，使其支持Spring MVC注解，另外还整合了Ribbon和Eureka，从而使得Feign的使用更加方便。

2. 同Ribbon对比

Ribbon还是采用暴露url的方式调用服务，而Feign可以使用如下方法调用。

productCenterFeignApi.getString()

其中productCenterFeignApi就是Feign客户端。

3. 示例

3.1 简单使用

父工程参考这篇文章里的父工程Nacos使用

3.1.1 新建子工程feign-api

pom文件:

<?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">
    <parent>
        <artifactId>Learn</artifactId>
        <groupId>zyz.springCloudAlibaba</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>feign-api</artifactId>

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

接口类:

package com.zyz.feignapi;

import com.zyz.comfig.ProductCenterFeignConfig;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;

@FeignClient(name = "product-center")
public interface ProductCenterFeignApi {

    @RequestMapping("/getString")
    String getString();
}

3.1.2 新建子工程feign-order

pom文件:

<?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">
    <parent>
        <artifactId>Learn</artifactId>
        <groupId>zyz.springCloudAlibaba</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>feign-order</artifactId>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>

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

        <!--加入nocas-client-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-alibaba-nacos-discovery</artifactId>
        </dependency>


        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>21.0</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>zyz.springCloudAlibaba</groupId>
            <artifactId>feign-api</artifactId>
            <version>1.0-SNAPSHOT</version>
            <scope>compile</scope>
        </dependency>

    </dependencies>


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

</project>

Controller类:

package com.zyz.controller;

import com.zyz.feignapi.ProductCenterFeignApi;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class OrderController {

    @Autowired
    private ProductCenterFeignApi productCenterFeignApi;

    @RequestMapping("/get")
    public String get(){
        return productCenterFeignApi.getString();
    }
}

启动类:

package com.zyz;

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
public class FeignOrderApplication {

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

}

配置文件为:

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
  application:
    name: order-center

server:
  port: 8801

3.1.3 新建子工程feign-product

pom文件为:

<?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">
    <parent>
        <artifactId>Learn</artifactId>
        <groupId>zyz.springCloudAlibaba</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>feign-product</artifactId>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>

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

        <!--加入nocas-client-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-alibaba-nacos-discovery</artifactId>
        </dependency>


        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>21.0</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>zyz.springCloudAlibaba</groupId>
            <artifactId>feign-api</artifactId>
            <version>1.0-SNAPSHOT</version>
            <scope>compile</scope>
        </dependency>

    </dependencies>


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

</project>

Controller类:

package com.zyz.controller;

import com.zyz.feignapi.ProductCenterFeignApi;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ProductController implements ProductCenterFeignApi {

    @Override
    @RequestMapping("/getString")
    public String getString() {
        System.out.println("调用我啦");
        return "Hello";
    }
}

启动类:

package com.zyz;

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

@SpringBootApplication
@EnableDiscoveryClient
public class FeignProductApplication {

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

配置文件:

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
  application:
    name: product-center

server:
  port: 8804

分别启动feign-product和feign-order项目，并访问feign-order里的接口，可以成功看到输出。

3.2 加入日志

默认情况下，Feign调用在客户端是没有日志的，这里把日志功能添加进去。

这里修改feign-api和feign-order这两个项目。

3.2.1 修改feign-api项目

新增配置类ProductCenterFeignConfig

package com.zyz.config;

import feign.Logger;
import org.springframework.context.annotation.Bean;

public class ProductCenterFeignConfig {

    @Bean
    public Logger.Level level() {
        return Logger.Level.BASIC;
    }

}

修改ProductCenterFeignApi接口

package com.zyz.feignapi;

import com.zyz.config.ProductCenterFeignConfig;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;

@FeignClient(name = "product-center", configuration = ProductCenterFeignConfig.class)
public interface ProductCenterFeignApi {

    @RequestMapping("/getString")
    String getString();
}

3.2.3 修改feign-order项目

修改配置文件

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
  application:
    name: order-center

server:
  port: 8801

#开启日志
logging:
  level:
    com:
      zyz:
        feignapi: debug

3.3 与Ribbon配合使用，加入负载均衡逻辑

由于Feign底层支持Ribbon，所以这里只需要在配置文件中添加配置即可。

修改feign-order的配置文件

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
  application:
    name: order-center

server:
  port: 8801


#负载均衡配置
product-center:
  ribbon:
    NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RoundRobinRule

#开启ribbon饥饿加载,解决微服务调用第一次很慢的情况下
ribbon:
  eager-load:
    enabled: true
    #可以指定多个微服务用逗号分隔
    clients: product-center

#开启日志
logging:
  level:
    com:
      zyz:
        feignapi: debug

大功告成，可以自行测试一下。

Spring Cloud Alibaba之Feign使用