Spring Cloud Feign 使用方法與性能優化

1. feign自定義Configuration和root 容器有效隔離。

用@Configuration注解
不能在主@ComponentScan (or @SpringBootApplication)范圍內，從其包名上分離
注意避免包掃描重疊，最好的方法是明確的指定包名

2. Spring Cloud Netflix 提供了默認的Bean類型:

Decoder feignDecoder: ResponseEntityDecoder (which wraps a SpringDecoder)
Encoder feignEncoder: SpringEncoder
Logger feignLogger: Slf4jLogger
Contract feignContract: SpringMvcContract
Feign.Builder feignBuilder: HystrixFeign.Builder

3. Spring Cloud Netflix沒有提供默認值，但仍然可以在feign上下文配置中創建：

Logger.Level
Retryer
ErrorDecoder
Request.Options
Collection

4. 自定義feign的消息編碼解碼器：

不要在如下代碼中getObject方法內new 對象，外部會頻繁調用getObject方法。

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

5. 注意測試環境和生產環境，注意正確使用feign日志級別。

6. apacheHttpclient或者其他client的正確配置：

apacheHttpclient自定義配置放在spring root context，不要在FeignContext，否則不會起作用。
apacheHttpclient 連接池配置合理地連接和其他參數

7. Feign配置

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#Hystrix支持，如果為true，hystrix庫必須在classpath中
feign.hystrix.enabled=false

#請求和響應GZIP壓縮支持
feign.compression.request.enabled=true
feign.compression.response.enabled=true
#支持壓縮的mime types
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

8. Logger.Level支持

必須為每一個Feign Client配置來告訴Feign如何輸出日志，可選：

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 正確的使用方法

配置的fallback class也必須在FeignClient Configuration中實例化，否則會報
java.lang.IllegalStateException: No fallback instance of type class異常。

例子：

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@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();
}

}

10. 使用Feign Client 和@RequestMapping時，注意事項

當前工程中有和Feign Client中一樣的Endpoint時，Feign Client的類上不能用@RequestMapping注解否則，當前工程該endpoint http請求且使用accpet時會報404.

下面的例子：

有一個 Controller

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@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();
}
}

有一個Feign Client

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@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();

}

if @RequestMapping is used on class, when invoke http /v1/card/balance, like this :

如果 @RequestMapping注解被用在FeignClient類上，當像如下代碼請求/v1/card/balance時，注意有Accept header：

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Content-Type: application/json
Accept: application/json

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

那么會返回 404。

如果不包含Accept header時請求，則是OK：

1 2	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,請求也是ok，無論是否包含Accept:

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@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();

}