SpringBoot2 整合 SpringCloud Feign 實例

1. 簡介

Feign 是一個聲明式的僞Http客戶端，使用時只需要創建一個接口並註解。
Feign 默認集成了 Ribbon，並和 Eureka 結合，默認實現了負載均衡的效果。

2. 工程實例

在這篇文章： SpringBoot2 整合 SpringCloud Ribbon 實現負載均衡實例 中我們使用RestTemplate+Ribbon去消費服務，本篇文章主要講述如何通過Feign去消費服務。

工程目錄如下圖所示：

root 工程 spring-study，root 工程的 pom.xml 如下所示：

<?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>com.syrdbt</groupId>
    <artifactId>study</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>springcloud-study-eureka-server</module>
        <module>springcloud-study-feign</module>
        <module>springcloud-study-hello-service</module>
    </modules>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.7.RELEASE</version>
        <relativePath/>
    </parent>

    <properties>
        <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>Finchley.RELEASE</spring-cloud.version>
    </properties>

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

    <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>
        </dependencies>
    </dependencyManagement>

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

</project>

2.1 註冊中心 springcloud-study-eureka-server

工程目錄如下所示：

2.1.1 依賴 pom.xml

pom.xml 的依賴如下所示：

<?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>study</artifactId>
        <groupId>com.syrdbt</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <modelVersion>4.0.0</modelVersion>

    <artifactId>eurkea-server</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>
    </dependencies>
</project>

2.1.2 配置文件 application.properties

配置文件如下所示：

# 服務註冊中心端口號
server.port=8761
# 服務註冊中心主機名
eureka.instance.hostname=127.0.0.1
# 不向註冊中心註冊自己
eureka.client.register-with-eureka=false
# 不需要檢索服務
eureka.client.fetch-registry=false
# 註冊中心地址，會自動填充 主機名 和 端口號
eureka.client.service-url.defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

2.1.3 啓動類 EurekaServerApplication.java

package com.syrdbt.study.eureka.server;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

/**
 * @author syrdbt
 * @date 2019-10-12
 */
@EnableEurekaServer
@SpringBootApplication
public class EurekaServerApplication {

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

}

2.2 服務提供者 springcloud-study-hello-service

工程目錄如下所示：

2.2.1 依賴 pom.xml

pom.xml 如下所示：

<?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>study</artifactId>
        <groupId>com.syrdbt</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>hello-service</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

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

2.2.2 配置文件 application.yml

eureka:
  client:
    serviceUrl:
      #註冊中心的地址
      defaultZone: http://localhost:8761/eureka/
server:
  #當前服務端口號
  port: 8762
spring:
  application:
    #當前應用名稱,當前應用的名稱
    name: service-hi

2.2.3 控制器 HelloController.java

package com.syrdbt.study.hello.service.controller;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author syrdbt
 * @date 2019-10-12
 */
@RestController
public class HelloController {
    @Value("${server.port}")
    private String port;

    @RequestMapping(value = "hello", method = RequestMethod.GET)
    public String index() {
        return "eurekaClient：Hello World " + this.port;
    }
}

2.2.4 啓動類 HelloServiceApplication.java

package com.syrdbt.study.hello.service;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

/**
 * @author syrdbt
 * @date 2019-10-12
 */
@SpringBootApplication
@EnableEurekaClient
public class HelloServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(HelloServiceApplication.class, args);
    }
}

2.3 springcloud-study-feign

2.3.1 依賴 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">
    <parent>
        <artifactId>study</artifactId>
        <groupId>com.syrdbt</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>feign</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
    </dependencies>
</project>

2.3.2 配置文件 application.yml

application.yml：

server:
  port: 8765
spring:
  application:
    # 該服務的名字
    name: server-feign
eureka:
  client:
    serviceUrl:
      # eureka服務的地址
      defaultZone: http://localhost:8761/eureka/

2.3.3 Fegin 接口 HelloFeign

通過@ FeignClient（“服務名”），來指定調用哪個服務。下面的示例中調用了service-hi服務的“/hello”接口，HelloFeign.java 代碼如下：

package com.syrdbt.study.feign;

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

/**
 * @author syrdbt
 * @date 2019-10-12
 */
@FeignClient(name = "service-hi")
public interface HelloFeign {

    @RequestMapping(value="/hello")
    String hello();
}

2.3.4 調用 feign 接口的控制器

HelloController.java，通過上面定義的Feign客戶端 HelloFeign 來消費服務。

package com.syrdbt.study.feign.controller;

import com.syrdbt.study.feign.HelloFeign;
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;

/**
 * @author syrdbt
 * @date 2019-10-12
 */
@RestController
public class HelloController {
    @Autowired
    private HelloFeign helloFeign;

    @GetMapping(value="/hello")
    public String getHi() {
        return helloFeign.hello();
    }
}

2.3.5 啓動類 FeignApplication

package com.syrdbt.study.feign;

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

/**
 * @author syrdbt
 * @date 2019-10-12
 */
@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@EnableDiscoveryClient
public class FeignApplication {
    public static void main(String[] args) {
        SpringApplication.run(FeignApplication.class, args);
    }
}

3. 啓動並測試

需要啓動4個實例。
⚠️注意：HelloServiceApplication 需要啓動兩個，兩個的端口號分別爲 8762 和 8763 。
IDEA 啓動多實例教程：https://www.cnblogs.com/wuxun1997/p/11208519.html。

3.1 註冊中心的情況

訪問 http://localhost:8761/ 。
註冊中心註冊的 實例如下所示：

3.2 測試訪問

訪問：http://localhost:8765/hello 。
運行截圖如下所示：

參考文獻

• SpringCloud 微服務實戰 - 作者 ：崔永超老師
• https://www.fangzhipeng.com/springcloud/2018/08/03/sc-f3-feign.html