Feign正确的使用姿势和性能优化注意事项

1. feign自定义Configuration和root 容器有效隔离。

• 用@Configuration注解
• 不能在主@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

2. Spring Cloud Netflix 提供了默认的Bean类型:

• 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没有提供默认值，但仍然可以在feign上下文配置中创建：

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

4. 自定义feign的消息编码解码器：

不要在如下代码中getObject方法内new 对象，外部会频繁调用getObject方法。

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

5. 注意测试环境和生产环境，注意正确使用feign日志级别。

6. apacheHttpclient或者其他client的正确配置：

• apacheHttpclient自定义配置放在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

7. Feign配置

#Hystrix支持，如果为true，hystrix库必须在classpath中
feign.hystrix.enabled=false
 
#请求和响应GZIP压缩支持
feign.compression.request.enabled=true
feign.compression.response.enabled=true
#支持压缩的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();
        }
        
    }
    

10. 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accpet时会报404.

下面的例子：

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();

}

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

如果 @RequestMapping注解被用在FeignClient类上，当像如下代码请求/v1/card/balance时，注意有Accept header：

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

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

那么会返回 404。

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();

}