作为Spring Cloud的子项目之一，Spring Cloud OpenFeign以将OpenFeign集成到Spring Boot应用中的方式，为微服务架构下服务之间的调用提供了解决方案。首先，利用了OpenFeign的声明式方式定义Web服务客户端；其次还更进一步，通过集成Ribbon或Eureka实现负载均衡的HTTP客户端。
  OpenFeign 可以使消费者将提供者提供的服务名伪装为接口进行消费，消费者只需使用“Service 接口+ 注解”的方式。即可直接调用 Service 接口方法，而无需再使用 RestTemplate 了。其实原理还是使用RestTemplate，而通过Feign（伪装）成我们熟悉的习惯。
  GitEgg框架除了新建Fegin服务之外，还定义实现了消费者Fegin-api，在其他微服务调用的时候，只需要引入Fegin-api即可直接调用，不需要在自己重复开发消费者调用接口。

1、在GitEgg-Platform工程的子工程gitegg-platform-cloud中引入spring-cloud-starter-openfeign依赖,重新install GitEgg-Platform工程，然后GitEgg-Cloud项目需要重新在IDEA中执行Reload All Maven Projects。

<?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>GitEgg-Platform</artifactId>
        <groupId>com.gitegg.platform</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>gitegg-platform-cloud</artifactId>
    <name>${project.artifactId}</name>
    <version>${project.parent.version}</version>
    <packaging>jar</packaging>

    <dependencies>
        <!-- Nacos 服务注册发现-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
        <!-- Nacos 分布式配置-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
        </dependency>
        <!-- OpenFeign 微服务调用解决方案-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
    </dependencies>

</project>

  我们从系统架构设计方面考虑，GitEgg-Cloud下的gitegg-service作为业务逻辑处理模块，gitegg-service-api作为微服务统一对外提供接口的模块，这里在测试的时候需要用到两个微服务之间的调用，我们这里在gitegg-service下gitegg-service-base里面新建测试代码，和gitegg-service-system之间相互调用。注意，这里需要说明，gitegg-service-api并不是继承gitegg-service做业务扩展，而是对外提供接口的抽象，比如现在有A、B、C三个系统A、B都需要调用C的同一个方法，如果按照业务逻辑来罗列代码的话，那么就需要在A和B中写相同的调用方法来调用C，这里我们抽出来一个api模块，专门存放调用微服务C的调用方法，在使用时，A和B只需要引入C的jar包即可直接使用调用方法。
2、在gitegg-service-system-api工程中，引入SpringBoot，SpringCloud，Swagger2的依赖，新建ISystemFeign.java和ApiSystemDTO.java，作为OpenFeign调用微服务的公共方法：

<?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>GitEgg-Cloud</artifactId>
        <groupId>com.gitegg.cloud</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>gitegg-service-api</artifactId>
    <name>${project.artifactId}</name>
    <version>${project.parent.version}</version>
    <packaging>pom</packaging>
    <modules>
        <module>gitegg-service-base-api</module>
        <module>gitegg-service-bigdata-api</module>
        <module>gitegg-service-system-api</module>
    </modules>

    <dependencies>
        <!-- gitegg Spring Boot自定义及扩展 -->
        <dependency>
            <groupId>com.gitegg.platform</groupId>
            <artifactId>gitegg-platform-boot</artifactId>
        </dependency>
        <!-- gitegg Spring Cloud自定义及扩展 -->
        <dependency>
            <groupId>com.gitegg.platform</groupId>
            <artifactId>gitegg-platform-cloud</artifactId>
        </dependency>
        <!-- gitegg swagger2-knife4j -->
        <dependency>
            <groupId>com.gitegg.platform</groupId>
            <artifactId>gitegg-platform-swagger</artifactId>
        </dependency>
    </dependencies>


</project>

package com.gitegg.service.system.api.feign;

import com.gitegg.platform.boot.common.base.Result;
import com.gitegg.service.system.api.dto.ApiSystemDTO;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient(name = "gitegg-service-system")
public interface ISystemFeign {

    /**
     * OpenFeign测试Get
     *
     * @param id
     * @return
     */
    @GetMapping("/system/api/by/id")
    Result<Object> querySystemById(@RequestParam("id") Long id);

    /**
     * OpenFeign测试Post
     *
     * @param apiSystemDTO
     * @return ApiSystemDTO
     */
    @PostMapping("/system/api/by/dto")
    Result<ApiSystemDTO> querySystemByDto(@RequestBody ApiSystemDTO apiSystemDTO);
}

package com.gitegg.service.system.api.dto;

import lombok.Data;

import javax.validation.constraints.Max;
import javax.validation.constraints.Min;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;

@Data
public class ApiSystemDTO {

    @NotNull
    @Min(value = 10, message = "id必须大于10")
    @Max(value = 150, message = "id必须小于150")
    private Long id;

    @NotNull(message = "名称不能为空")
    @Size(min = 3, max = 20, message = "名称长度必须在3-20之间")
    private String name;
    
}

2、在gitegg-service-system工程中，修改SystemController.java,添加需要被微服务调用的方法:

package com.gitegg.service.system.controller;

import com.gitegg.platform.boot.common.base.Result;
import com.gitegg.service.system.dto.SystemDTO;
import com.gitegg.service.system.service.ISystemService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import lombok.RequiredArgsConstructor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.web.bind.annotation.*;

import javax.validation.Valid;

@RestController
@RequestMapping(value = "system")
@RequiredArgsConstructor(onConstructor_ = @Autowired)
@Api(tags = "gitegg-system")
@RefreshScope
public class SystemController {

    private final ISystemService systemService;

    @Value("${spring.datasource.maxActive}")
    private String nacosMaxActiveType;

    @GetMapping(value = "list")
    @ApiOperation(value = "system list接口")
    public Object list() {
        return systemService.list();
    }


    @GetMapping(value = "page")
    @ApiOperation(value = "system page接口")
    public Object page() {
        return systemService.page();
    }

    @GetMapping(value = "exception")
    @ApiOperation(value = "自定义异常及返回测试接口")
    public Result<String> exception() {
        return Result.data(systemService.exception());
    }

    @PostMapping(value = "valid")
    @ApiOperation(value = "参数校验测试接口")
    public Result<SystemDTO> valid(@Valid @RequestBody SystemDTO systemDTO) {
        return Result.data(systemDTO);
    }

    @PostMapping(value = "nacos")
    @ApiOperation(value = "Nacos读取配置文件测试接口")
    public Result<String> nacos() {
        return Result.data(nacosMaxActiveType);
    }

    @GetMapping(value = "api/by/id")
    @ApiOperation(value = "Fegin Get调用测试接口")
    public Result<Object> feginById(@RequestParam("id") String id) {
        return Result.data(systemService.list());
    }

    @PostMapping(value = "api/by/dto")
    @ApiOperation(value = "Fegin Post调用测试接口")
    public Result<Object> feginByDto(@Valid @RequestBody SystemDTO systemDTO) {
        return Result.data(systemDTO);
    }
}

3、参照gitegg-service-system工程，在gitegg-service-base工程下，引入gitegg-service-system-api依赖，新建BaseController.java、GitEggBaseApplication.java、bootstrap.yml作为服务调用方：
pom.xml:

    <dependencies>
        <!-- gitegg-service-system 的fegin公共调用方法 -->
        <dependency>
            <groupId>com.gitegg.cloud</groupId>
            <artifactId>gitegg-service-system-api</artifactId>
            <version>${project.parent.version}</version>
        </dependency>
    </dependencies>

BaseController.java:

package com.gitegg.service.base.controller;

import com.gitegg.platform.boot.common.base.Result;
import com.gitegg.service.system.api.dto.ApiSystemDTO;
import com.gitegg.service.system.api.feign.ISystemFeign;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import lombok.RequiredArgsConstructor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.web.bind.annotation.*;

import javax.validation.Valid;

@RestController
@RequestMapping(value = "base")
@RequiredArgsConstructor(onConstructor_ = @Autowired)
@Api(tags = "gitegg-base")
@RefreshScope
public class BaseController {

    private final ISystemFeign systemFeign;

    @GetMapping(value = "api/by/id")
    @ApiOperation(value = "Fegin Get调用测试接口")
    public Result<Object> feginById(@RequestParam("id") Long id) {
        return Result.data(systemFeign.querySystemById(id));
    }

    @PostMapping(value = "api/by/dto")
    @ApiOperation(value = "Fegin Post调用测试接口")
    public Result<Object> feginByDto(@Valid @RequestBody ApiSystemDTO systemDTO) {
        return Result.data(systemFeign.querySystemByDto(systemDTO));
    }

}

GitEggBaseApplication.java:

package com.gitegg.service.base;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.context.annotation.ComponentScan;

/**
 * gitegg-base 启动类
 */
@EnableDiscoveryClient
@EnableFeignClients(basePackages = "com.gitegg")
@ComponentScan(basePackages = "com.gitegg")
@MapperScan("com.gitegg.*.*.mapper")
@SpringBootApplication
public class GitEggBaseApplication {

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

}

bootstrap.yml:

server:
  port: 8002
spring:
  application:
    name: gitegg-service-base
  cloud:
    nacos:
      discovery:
        server-addr: 127.0.0.1:8848
      config:
        server-addr: 127.0.0.1:8848
        file-extension: yaml
        prefix: gitegg-service-system
        group: DEFAULT_GROUP
        enabled: true

4、分别启动gitegg-service-base和gitegg-service-system项目，打开浏览器，访问http://127.0.0.1:8002/doc.html（这里gitegg-service-base的端口设置为8002，所以访问gitegg-service-base的服务进行测试），在页面左侧菜单分别点击Fegin Get调用测试接口和Fegin Post调用测试接口，可以查看微服务调用成功

image.png

image.png

本文源码在https://gitee.com/wmz1930/GitEgg 的chapter-11分支。

GitEgg-Cloud是一款基于SpringCloud整合搭建的企业级微服务应用开发框架，开源项目地址:

Gitee: https://gitee.com/wmz1930/GitEgg
GitHub: https://github.com/wmz1930/GitEgg

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