spring boot 2.0.3+spring cloud (Finchley)3、声明式调用Feign

Feign受Retrofix、JAXRS-2.0和WebSocket影响,采用了声明式API接口的风格,将Java Http客户端绑定到他的内部。Feign的首要目标是将Java Http客户端调用过程变得简单。

源码地址:https://github.com/OpenFeign/feign

本章案例基于上一章,可参考:

spring boot 2.0.3+spring cloud (Finchley)1、搭建Eureka 以及构建高可用Eureka Server集群 

spring boot 2.0.3+spring cloud (Finchley)2、搭建负载均衡Ribbon (Eureka+Ribbon+RestTemplate)

新建module工程eureka-feign-client。pom文件引入相关依赖,包括主maven工程的pom文件,eureka client起步依赖,feign的起步依赖,web的起步依赖(已在主maven工程pom中配置)

<?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.cralor</groupId>
    <artifactId>eureka-feign-client</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>eureka-feign-client</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>com.cralor</groupId>
        <artifactId>chap7-feign</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <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>

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

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

</project>

配置文件做相关配置

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

在程序的启动类加上注解@EnableFeignClients开启Feign Client功能

@EnableFeignClients
@SpringBootApplication
public class EurekaFeignClientApplication {

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

通过以上步骤,该程序已经具备了Feign的功能,现在来实现一个简单的feign client。新建一个EurekaClientFeign的接口,在接口上加@FeignClient注解来声明一个Feign Client。value为远程调用其他服务的服务名,FeignConfig.class为配置类,在EurekaClientFeign内部有一个sayHiFromClientEureka()的方法,该方法通过Feign来调用eureka-client服务的“/hi”的aipi接口。

@Component
@FeignClient(value = "eureka-client",configuration = FeignConfig.class)
public interface EurekaClientFeign {
    @GetMapping(value = "/hi")
    String sayHiFromClientEureka(@RequestParam(value = "name")String name);
}

在FeignConfig类上加上@Configuration注解,表明这是一个配置类,并注入一个BeanName为feignRetryer的Retryer的Bean。可使feign在远程调用失败后会进行重试。

@Configuration
public class FeignConfig {
    @Bean
    public Retryer feignRetryer(){
        return new Retryer.Default(100,TimeUnit.SECONDS.toMillis(1),5);
    }
}

service层HiService类注入EurekaClient的Bean

@Service
public class HiService {
    @Autowired
    EurekaClientFeign eurekaClientFeign;

    public  String sayHi(String name){
        return eurekaClientFeign.sayHiFromClientEureka(name);
    }
}

新建HiController类,调用HiService的sayHi()方法,HiService通过EurekaClientFeign远程调用eureka-client服务的API接口“/hi”。

@RestController
public class HiController {
    @Autowired
    HiService hiService;

    @GetMapping("/hi")
    public String sayHi(@RequestParam(defaultValue = "cralor",required = false)String name){
        return hiService.sayHi(name);
    }
}

启动eureka-server工程,端口号8761,启动两个eureka-client工程的实例,端口号8762、8763,启动eureka-feign-client工程,端口号8765。在浏览器多次访问http://localhost:8765/hi,浏览器会轮流显示

            

可见Feign Client远程调用了eureka-client的服务(存在端口号为8762和8763的两个实例)的“/hi”API接口,feign client有负载均衡的能力。

 

总结:feign源码实现过程如下

1.首先通过@EnableFeignClients注解开启FeignClient功能。只有这个注解的存在,程序启动时才会开启对@FeignConfig注解的包的扫描,

2.根据Feig的规则实现接口,并在接口上面加上@FeignClient注解。

3.程序启动后会进行包扫描,扫描所有@FeignClient注解的类,并将这些信息注入IOC容器中。

4.当接口的方法被调用时,通过JDK的代理来生成具体的RequestTemplate模板对象。

5.根据RequestTemplate再生成Http请求的Request对象。

6.Request对象交给Client去处理,其中Client的网络请求框架可以是HttpURLConnection、HttpClient和OkHttp。

7.最后Client被封装到LoadBalanceClient类,这个类结合类Ribbon做到了负载均衡。

 

 参考:https://windmt.com/2018/04/15/spring-cloud-3-service-producer-and-consumer/#Spring-Cloud-Feign

 

 案例代码地址:https://github.com/cralor7/springcloud

 

 

posted @ 2018-06-26 13:38  cralor  阅读(6634)  评论(0编辑  收藏  举报