spring-cloud feign(一)负载均衡

一、环境

spring boot 2.x

spring cloud （Finchley SR2以上版本)

二、引入feign依赖

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

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-dependencies</artifactId>
			<version>${spring-cloud.version}</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

三、简单使用

服务端

提供和客户端调用的接口路径和参数一致的方法即可

方法一

测试使用

@GetMapping("/hello/{userId}")
public String hello(@PathVariable String userId) {
    String services = "Services: " + discoveryClient.getServices()+" ip :"+ip;
    services += "\n " + userId;
    
    System.out.println(services);
    return services;
}

方法二

使用客户端相同接口

@RestController
public class HelloClientServiceImpl extends ServiceImpl<MenuMapper, Menu> implements HelloClient {
	@Override
    public String hello(@PathVariable String userId) {
        // do something ...
    }
}

客户端

1. Application类中

添加@EnableFeignClients

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class LwpConSumerApplication {

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

2. 定义接口

• HelloClient中@RequestMapping声明的路径和参数必须与服务提供方一致。 客户端可以把这两个接口合并在一起

• 接口可以传递对象参数，这个参数必须实现序列化接口

public interface HelloClient {
	@RequestMapping(method = RequestMethod.GET, value = "/hello/{userId}")
	String hello(@PathVariable String userId);
}

HelloClientService实现HelloClient方法，@FeignClient(“PROVIDER”)中PROVIDER为需要调用的服务

@FeignClient("PROVIDER")
public interface HelloClientService extends HelloClient{

}

3. 使用

在需要使用的地方@Autowired即可

@Autowired
private HelloClientService helloClientService;

@GetMapping("/test3")
public String test3() {
	return helloClientService.hello(String.valueOf(System.currentTimeMillis()));
}

四、 官方文档

官方文档地址 http://cloud.spring.io/spring-cloud-static/Edgware.SR2/single/spring-cloud.html#spring-cloud-feign

下面的内容为随意黏贴，如果看不明白可以看官方文档。

占位符支持

Placeholders are supported in the name and url attributes.

@FeignClient(name = "${feign.name}", url = "${feign.url}")
public interface StoreClient {
    //..
}

常用参数

Spring Cloud Netflix provides the following beans by default for feign (BeanType beanName: ClassName):

• Decoder feignDecoder: ResponseEntityDecoder (which wraps a SpringDecoder)
• Encoder feignEncoder: SpringEncoder
• Logger feignLogger: Slf4jLogger
• Contract feignContract: SpringMvcContract
• Feign.Builder feignBuilder: HystrixFeign.Builder
• Client feignClient: if Ribbon is enabled it is a LoadBalancerFeignClient, otherwise the default feign client is used.

The OkHttpClient and ApacheHttpClient feign clients can be used by setting feign.okhttp.enabled or feign.httpclient.enabled to true, respectively, and having them on the classpath. You can customize the HTTP client used by providing a bean of either ClosableHttpClient when using Apache or OkHttpClient whe using OK HTTP.

Spring Cloud Netflix does not provide the following beans by default for feign, but still looks up beans of these types from the application context to create the feign client:

• Logger.Level
• Retryer
• ErrorDecoder
• Request.Options
• Collection<RequestInterceptor>
• SetterFactory

Creating a bean of one of those type and placing it in a @FeignClient configuration (such as FooConfiguration above) allows you to override each one of the beans described. Example:

@Configuration
public class FooConfiguration {
    @Bean
    public Contract feignContract() {
        return new feign.Contract.Default();
    }

    @Bean
    public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
        return new BasicAuthRequestInterceptor("user", "password");
    }
}

使用配置文件进行配置

This replaces the SpringMvcContract with feign.Contract.Default and adds a RequestInterceptor to the collection of RequestInterceptor.

@FeignClient also can be configured using configuration properties.

application.yml

feign:
  client:
    config:
      feignName:
        connectTimeout: 5000
        readTimeout: 5000
        loggerLevel: full
        errorDecoder: com.example.SimpleErrorDecoder
        retryer: com.example.SimpleRetryer
        requestInterceptors:
          - com.example.FooRequestInterceptor
          - com.example.BarRequestInterceptor
        decode404: false

Default configurations can be specified in the @EnableFeignClients attribute defaultConfiguration in a similar manner as described above. The difference is that this configuration will apply to all feign clients.

If you prefer using configuration properties to configured all @FeignClient, you can create configuration properties with default feign name.

application.yml

feign:
  client:
    config:
      default:
        connectTimeout: 5000
        readTimeout: 5000
        loggerLevel: basic

If we create both @Configuration bean and configuration properties, configuration properties will win. It will override @Configuration values. But if you want to change the priority to @Configuration, you can change feign.client.default-to-properties to false.

If you need to use ThreadLocal bound variables in your RequestInterceptors you will need to either set the thread isolation strategy for Hystrix to SEMAPHORE or disable Hystrix in Feign.

application.yml

# To disable Hystrix in Feign
feign:
  hystrix:
    enabled: false

# To set thread isolation to SEMAPHORE
hystrix:
  command:
    default:
      execution:
        isolation:
          strategy: SEMAPHORE

手动创建Feign Clients

Creating Feign Clients Manually

In some cases it might be necessary to customize your Feign Clients in a way that is not possible using the methods above. In this case you can create Clients using theFeign Builder API. Below is an example which creates two Feign Clients with the same interface but configures each one with a separate request interceptor.

@Import(FeignClientsConfiguration.class)
class FooController {

	private FooClient fooClient;

	private FooClient adminClient;

    	@Autowired
	public FooController(
			Decoder decoder, Encoder encoder, Client client) {
		this.fooClient = Feign.builder().client(client)
				.encoder(encoder)
				.decoder(decoder)
				.requestInterceptor(new BasicAuthRequestInterceptor("user", "user"))
				.target(FooClient.class, "http://PROD-SVC");
		this.adminClient = Feign.builder().client(client)
				.encoder(encoder)
				.decoder(decoder)
				.requestInterceptor(new BasicAuthRequestInterceptor("admin", "admin"))
				.target(FooClient.class, "http://PROD-SVC");
    }
}

熔断器使用

17.4 Feign Hystrix Support

If Hystrix is on the classpath and feign.hystrix.enabled=true, Feign will wrap all methods with a circuit breaker. Returning a com.netflix.hystrix.HystrixCommand is also available. This lets you use reactive patterns (with a call to .toObservable() or .observe() or asynchronous use (with a call to .queue()).

To disable Hystrix support on a per-client basis create a vanilla Feign.Builder with the “prototype” scope, e.g.:

@Configuration
public class FooConfiguration {
    	@Bean
	@Scope("prototype")
	public Feign.Builder feignBuilder() {
		return Feign.builder();
	}
}

Prior to the Spring Cloud Dalston release, if Hystrix was on the classpath Feign would have wrapped all methods in a circuit breaker by default. This default behavior was changed in Spring Cloud Dalston in favor for an opt-in approach.

17.5 Feign Hystrix Fallbacks

Hystrix supports the notion of a fallback: a default code path that is executed when they circuit is open or there is an error. To enable fallbacks for a given @FeignClientset the fallback attribute to the class name that implements the fallback. You also need to declare your implementation as a Spring bean.

@FeignClient(name = "hello", fallback = HystrixClientFallback.class)
protected interface HystrixClient {
    @RequestMapping(method = RequestMethod.GET, value = "/hello")
    Hello iFailSometimes();
}

static class HystrixClientFallback implements HystrixClient {
    @Override
    public Hello iFailSometimes() {
        return new Hello("fallback");
    }
}

If one needs access to the cause that made the fallback trigger, one can use the fallbackFactory attribute inside @FeignClient.

@FeignClient(name = "hello", fallbackFactory = HystrixClientFallbackFactory.class)
protected interface HystrixClient {
	@RequestMapping(method = RequestMethod.GET, value = "/hello")
	Hello iFailSometimes();
}

@Component
static class HystrixClientFallbackFactory implements FallbackFactory<HystrixClient> {
	@Override
	public HystrixClient create(Throwable cause) {
		return new HystrixClient() {
			@Override
			public Hello iFailSometimes() {
				return new Hello("fallback; reason was: " + cause.getMessage());
			}
		};
	}
}

There is a limitation with the implementation of fallbacks in Feign and how Hystrix fallbacks work. Fallbacks are currently not supported for methods that return com.netflix.hystrix.HystrixCommand and rx.Observable.