spring cloud学习——17. Declarative REST Client: Feign

17. Declarative REST Client: Feign

Feign是一个声明式的web service client

17.1. How to Include Feign

eureka服务器端口号是8761

服务提供者microservice-provider-user端口号是7900

服务消费者8011

pom.xml

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

服务提供者访问地址http://localhost:7900/demo/dd

启动类注解

@EnableEurekaClient
@SpringBootApplication
@EnableFeignClients

Feign接口

package com.ldgx.eshop.feign;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
@FeignClient("microservice-provider-user")//服务提供者spring.application.name=microservice-provider-user
public interface UserFeignClient {	
	@RequestMapping(value="/demo/dd",method = RequestMethod.GET)//服务提供者的访问路径是/demo/dd
	public String dd();
}

在controller里面使用

@Autowired
private UserFeignClient client;//调用Feign

17.2. Overriding Feign Defaults

注意：配置文件Configuration1 不能在@ComponentScan可以扫描的范围下面.如下面的配置文件，启动类是

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com/ldgx/eshop/MicroserviceCustomerMovie1Application.java

配置文件不在启动类的同包和子包下面

package com.ldgx.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import feign.Contract;
@Configuration
public class Configuration1 {	
	/**
	 * feignContract:Defines what annotations and values are valid on interfaces.	 * 
	 * @return 用的注解方式
	 */
	@Bean
    public Contract feignContract() {
        return new feign.Contract.Default();//feign.Contract.Default()的注解方法举例：@RequestLine("GET /repos/{owner}/{repo}/contributors")
    }
}

feign

package com.ldgx.eshop.feign;
import org.springframework.cloud.netflix.feign.FeignClient;
import com.ldgx.config.Configuration1;
import feign.RequestLine;
@FeignClient(name = "microservice-provider-user",configuration = Configuration1.class)//服务提供者spring.application.name=microservice-provider-user
public interface UserFeignClient {	
	//@RequestMapping(value="/demo/dd",method = RequestMethod.GET)//服务提供者的访问路径是/demo/dd
	 @RequestLine("GET /demo/dd")
	public String dd();
}

如果还用@RequestMapping(value="/demo/dd",method = RequestMethod.GET)会报错：

Caused by: java.lang.IllegalStateException: Method dd not annotated with HTTP method type (ex. GET, POST)

查看具体的注解（new feign.Contract.Default()），所以打开https://github.com/OpenFeign/feign查看

例子2，还是在原来的代码基础上

如果eureka服务端的地址是http://localhost:8761。

那么可以访问http://localhost:8761/eureka/apps/microservice-provider-user

microservice-provider-user是注册到eureka的服务提供者

Feign,访问改地址

package com.ldgx.eshop.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;

@FeignClient(name="xxxx",url = "http://localhost:8761")//eureka服务器地址是http://localhost:8761
public interface FeignClient2 {

	@RequestMapping(value="/eureka/apps/{serviceName}")//url的访问路径是http://localhost:8761/eureka/apps/microservice-provider-user
	public String findServiceInfoFromEurekaByServiceName(@PathVariable("serviceName") String serviceName);
}

controller

@RestController
public class UseDemoController {	
	@Autowired
	private FeignClient2 client2;
		
	@GetMapping("/{serviceName}")
	public String findServiceInfoFromEurekaByServiceName(@PathVariable String serviceName) {
		return client2.findServiceInfoFromEurekaByServiceName(serviceName);
	}
}

17.3. Creating Feign Clients Manually

在application.yml中增加配置

feign.hystrix.enabled: true

17.4. Feign Hystrix Support

启动类增加注解

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@EnableCircuitBreaker

package com.ldgx.eshop.feign;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
@FeignClient(name="microservice-provider-user", fallback = HystrixClientFallback.class)//服务提供者spring.application.name=microservice-provider-user
public interface UserFeignClient {	
	@RequestMapping(value="/demo",method = RequestMethod.GET)//服务提供者的访问路径是/demo
	public String dd();
}
@Component
class HystrixClientFallback implements UserFeignClient {//断路器
	@Override
	public String dd() {
		// TODO Auto-generated method stub
		return "===feign fall back===";
		//return null;
	}

}

17.5. Feign Hystrix Fallbacks
17.6. Feign and @Primary
17.7. Feign Inheritance Support
17.8. Feign request/response compression
17.9. Feign logging