SpringCloud项目构建（四）：Feign实现服务间的调用

1.1 Feign简介

　　Feign是简化Java HTTP客户端开发的工具（java-to-httpclient-binder），它的灵感来自于Retrofit、JAXRS-2.0和WebSocket。Feign的初衷是降低统一绑定Denominator到HTTP API的复杂度，不区分是否为restful

1.2 演示demo

(1)在上文创建的springCloudDemo_EurekaClient_A中创建com.xxx.controller包，并创建DemoCtroller类

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

@RequestMapping("/demo")
@CrossOrigin
@RestController
public class DemoController {


    @Value("${server.port}")
    private String serverPort;

    @GetMapping("/getPort")
    public String getPort(){
        return "我来自client-A，我的端口是 : " + serverPort;
    }
}

其中：@GetMapping为@RequestMapping(value = "xxx", method = RequestMethod.GET)的简写

　　　@RestController注解相当于@ResponseBody ＋ @Controller合在一起的作用

　　　@CrossOrigin是用来处理跨域请求的注解

（2）运行启动类，在注册中心可以看到发布的服务

（3）修改application.yml中的port 并取消single instance only 启动多个服务

（4）创建服务springCloudDemo_eurekaServer_B，并引入相关依赖

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<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>

（5）创建配置文件application.yml

eureka:
  client:
    service-url:
     defaultZone: http://127.0.0.1:6868/eureka/
  instance:
    prefer-ip-address: true
server:
  port: 7100
spring:
  application:
    name: clientb
（6）创建启动类

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;

@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableFeignClients
public class EurekaClientB {

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

（7）在springCloudDemo_eurekaServer_B模块下创建 com.xxx.client包，包下创建接口

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

@FeignClient("clienta")
public interface DemoClient {

    @GetMapping("/demo/getPort")
    public String getPort();
}

@FeignClient注解用于指定从哪个服务中调用功能，注意里面的名称与被调用的服务名保持一致，并且不能包含下划线。

@GetMapping注解用于对被调用的微服务进行地址映射。注意 @PathVariable注解一定要指定参数名称，否则出错

（8）在com.xxx.contorller下创建DemoController

import com.hongyin.client.DemoClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;


@RequestMapping("/demo")

@RestController
@CrossOrigin

public class DemoController {

    @Autowired
    private DemoClient demoClient;

    @GetMapping("getPort")
    public String getPort(){
        return demoClient.getPort();
    }
}

（9）启动springCloudDemo_eurekaClient_B测试：

可以看到我们通过微服务springCloudDemo_eurekaClient_B访问到了springCloudDemo_eurekaClient_A中的接口，完成了微服务之间的调用

SpringCloud项目构建（四）：Feign实现服务间的调用

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