前提概要

本章主要介绍相关的Fegin的相关配置和更深入一些的使用方式，如果对Fegin的不了解的话，可以先了

解一下，基于上一章之后，本章节属于完全不依赖于前一章，请放心观看本章内容。

用@Configuration注解不能在@ComponentScan or @SpringBootApplication范围内，从其包名上分离注意避免包扫描重叠，最好的方法是明确的指定包名。

Decoder feignDecoder：ResponseEntityDecoder (which wraps a SpringDecoder)

Encoder feignEncoder：SpringEncoder

Logger feignLogger: Slf4jLogger

Contract feignContract: SpringMvcContract

Feign.Builder feignBuilder: HystrixFeign.Builder

Logger.LevelRetryerErrorDecoderRequest.OptionsCollection

ObjectFactory messageConvertersObjectFactory = 
  new ObjectFactory() {
		@Override
		public HttpMessageConverters getObject() throws BeansException {
   		return httpMessageConverters;}
		};
}

• apacheHttpclient配置放在spring root context，不要在FeignContext，否则不会起作用。

• apacheHttpclient连接池配置合理地连接和其他参数

• 如果为true，hystrix库必须在classpath中

• feign.hystrix.enabled=false

• feign.compression.request.enabled=true

• feign.compression.response.enabled=true

• feign.compression.request.enabled=true

• feign.compression.request.mime-types=text/xml,application/xml,application/json

• feign.compression.request.min-request-size=2048

日志支持

• logging.level.project.user.UserClient: DEBUG

Logger.Level支持必须为每一个Feign Client配置来告诉Feign如何输出日志，可选：

• NONE,No logging (DEFAULT).

• BASIC, Log only the request method and URL and the response status code and execution time.

• HEADERS, Log the basic information along with request and response headers.

• FULL, Log the headers, body, and metadata for both requests and responses.9.

FeignClient.fallback 正确的使用方法配置的 fallback class 也必须在 FeignClient Configuration中实例化，否则会报java.lang.IllegalStateException: No fallback instance of type class异常。

例子

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


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

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

使用Feign Client 和@RequestMapping时，注意事项当前工程中有和Feign Client中一样的Endpoint时Feign Client的类上不能用@RequestMapping注解否则，当前工程该endpoint http请求且使用accept时会报404.

例子

有一个 Controller

@RestController
@RequestMapping("/v1/card")
public class IndexApi {
	 @PostMapping("balance")
	 @ResponseBody
	 public Info index() {
     Info.Builder builder = new Info.Builder();
     builder.withDetail("x", 2);
     builder.withDetail("y", 2);
     return builder.build();
	 }
}

有一个Feign Client

@FeignClient(name = "card",url = "http://localhost:7913",
           fallback = CardFeignClientFallback.class,
           configuration = FeignClientConfiguration.class)
@RequestMapping(value = "/v1/card")
public interface CardFeignClient {
	@RequestMapping(value = "/balance", method = RequestMethod.POST, 
  		produces = MediaType.APPLICATION_JSON_VALUE)
	Info info();
}

（1）如果 @RequestMapping注解被用在FeignClient类上，如下代码请求/v1/card/balance时，注意有,那么会返回 404。

Accept header：

Content-Type:application/jsonAccept:application/json

POST http://localhost:7913/v1/card/balance

（2）如果不包含Accept header时请求，则是OK：

Content-Type : application/json

POST http://localhost:7913/v1/card/balance

或者像下面不在Feign Client上使用@RequestMapping注解,请求也是ok，无论是否包含Accept:

@FeignClient(name = "card",
		url = "http://localhost:7913",
    fallback = CardFeignClientFallback.class,
    configuration = FeignClientConfiguration.class)
public interface CardFeignClient {
	  @RequestMapping(value = "/v1/card/balance", method = RequestMethod.POST,
                  produces = MediaType.APPLICATION_JSON_VALUE)
		Info info();
}