Spring Cloud Feign使用详解

背景

Feign是一个声明式的Web Service客户端，它的目的就是让Web Service调用更加简单。Feign提供了HTTP请求的模板，通过编写简单的接口和插入注解，就可以定义好HTTP请求的参数、格式、地址等信息。
而Feign则会完全代理HTTP请求，我们只需要像调用方法一样调用它就可以完成服务请求及相关处理。Feign整合了Ribbon和Hystrix(关于Hystrix我们后面再讲)，可以让我们不再需要显式地使用这两个组件。

特点

总起来说，Feign具有如下特性：

可插拔的注解支持，包括Feign注解和JAX-RS注解;
支持可插拔的HTTP编码器和解码器;
支持Hystrix和它的Fallback;
支持Ribbon的负载均衡;
支持HTTP请求和响应的压缩。

FeignClient注解的一些属性

快速开始

1.引入Feign

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

2.@FeignClient注解

SpringbootApplication启动类加上@FeignClient注解

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

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class ServiceFeignApplication {

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

}
//@EnableDiscoveryClient 和@EnableEurekaClient是等效的

3.yaml配置

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8765
spring:
  application:
    name: service-feign

4.Feign的使用

feign接口

@FeignClient(value = "service-hi")
public interface SchedualServiceHi {

    @RequestMapping(value = "/hi", method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam("name") String name);
}

访问接口

@RestController
public class HiController {

    @Autowired
    SchedualServiceHi schedualServiceHi;

    @GetMapping(value = "/hi")
    public String sayHi(@RequestParam String name){
        return schedualServiceHi.sayHiFromClientOne(name);

    }
}

实战

1.创建项目

创建一个Maven项目feign，新建2个module service-hi和service-feign

2.service-hi

pom

<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>

yml

server:
  port: 8763

spring:
  application:
    name: service-hi

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

ServiceHiApplication

@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@RestController
public class ServiceHiApplication {

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

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

    @RequestMapping("/hi")
    public String home(@RequestParam(value = "name", defaultValue = "forezp") String name) {
        return "hi " + name + " ,i am from port:" + port;
    }

}

3.service-feign

pom

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

yml

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8765
spring:
  application:
    name: service-feign

ServiceFeignApplication

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

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

}

SchedualServiceHi

@FeignClient(value = "service-hi")
public interface SchedualServiceHi {

    @RequestMapping(value = "/hi", method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam("name") String name);
}

HiController

@RestController
public class HiController {

    @Autowired
    SchedualServiceHi schedualServiceHi;

    @GetMapping(value = "/hi")
    public String sayHi(@RequestParam String name){
        return schedualServiceHi.sayHiFromClientOne(name);

    }
}