1. FeignClient注解
FeignClient注解被@Target(ElementType.TYPE)修饰，表示FeignClient注解的作用目标在接口上
@FeignClient(name = "demo-client", url = "https://api.fredia.io", configuration = DemoConfig.class)
public interface DemoClient{
@RequestMapping(value = "/user/info", method = RequestMethod.GET)
String searchRepo(@RequestParam("id") String id);
}
2. FeignClient源码
* Copyright 2013-2016 the original author or authors.
package org.springframework.cloud.netflix.feign;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.core.annotation.AliasFor;
/**
* Annotation for interfaces declaring that a REST client with that interface should be
* created (e.g. for autowiring into another component). If ribbon is available it will be
* used to load balance the backend requests, and the load balancer can be configured
* using a @RibbonClient with the same name (i.e. value) as the feign client.
*
* @author Spencer Gibb
* @author Venil Noronha
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FeignClient {
/**
* The name of the service with optional protocol prefix. Synonym for {@link #name()
* name}. A name must be specified for all clients, whether or not a url is provided.
* Can be specified as property key, eg: ${propertyKey}.
*/
@AliasFor("name")
String value() default "";
/**
* The service id with optional protocol prefix. Synonym for {@link #value() value}.
*
* @deprecated use {@link #name() name} instead
*/
@Deprecated
String serviceId() default "";
/**
* The service id with optional protocol prefix. Synonym for {@link #value() value}.
*/
@AliasFor("value")
String name() default "";
/**
* Sets the @Qualifier value for the feign client.
*/
String qualifier() default "";
/**
* An absolute URL or resolvable hostname (the protocol is optional).
*/
String url() default "";
/**
* Whether 404s should be decoded instead of throwing FeignExceptions
*/
boolean decode404() default false;
/**
* A custom @Configuration for the feign client. Can contain override
* @Bean definition for the pieces that make up the client, for instance
* {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
*
* @see FeignClientsConfiguration for the defaults
*/
Class[] configuration() default {};
/**
* Fallback class for the specified Feign client interface. The fallback class must
* implement the interface annotated by this annotation and be a valid spring bean.
*/
Class fallback() default void.class;
/**
* Define a fallback factory for the specified Feign client interface. The fallback
* factory must produce instances of fallback classes that implement the interface
* annotated by {@link FeignClient}. The fallback factory must be a valid spring
* bean.
*
* @see feign.hystrix.FallbackFactory for details.
*/
Class fallbackFactory() default void.class;
/**
* Path prefix to be used by all method-level mappings. Can be used with or without
* @RibbonClient.
*/
String path() default "";
/**
* Whether to mark the feign proxy as a primary bean. Defaults to true.
*/
boolean primary() default true;
}
3. FeignClient分析
声明接口之后，在代码中通过@Resource注入之后即可使用。@FeignClient标签的常用属性如下：
- name：指定FeignClient的名称，如果项目使用了Ribbon，name属性会作为微服务的名称，用于服务发现
- url: url一般用于调试，可以手动指定@FeignClient调用的地址
- decode404:当发生http 404错误时，如果该字段位true，会调用decoder进行解码，否则抛出FeignException
- configuration: Feign配置类，可以自定义Feign的Encoder、Decoder、LogLevel、Contract
- fallback: 定义容错的处理类，当调用远程接口失败或超时时，会调用对应接口的容错逻辑，fallback指定的类必须实现@FeignClient标记的接口
- fallbackFactory: 工厂类，用于生成fallback类示例，通过这个属性我们可以实现每个接口通用的容错逻辑，减少重复的代码
- path: 定义当前FeignClient的统一前缀
注意：在使用fallback属性时，需要使用@Component注解，保证fallback类被Spring容器扫描到,FeignConfiguration内容如下：
package com.macroflag.plusplatform.auth.server.configuration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.macroflag.plusplatform.auth.server.interceptor.ClientTokenInterceptor;
@Configuration
public class DemoConfig{
@Bean
ClientTokenInterceptor getClientTokenInterceptor() {
return new ClientTokenInterceptor();
}
}
在使用FeignClient时，Spring会按name创建不同的ApplicationContext，通过不同的Context来隔离FeignClient的配置信息，在使用配置类时，不能把配置类放到Spring App Component scan的路径下，否则，配置类会对所有FeignClient生效。
4. Feign Client 和@RequestMapping
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。
4.1 Controller：
@RestController
@RequestMapping("/demo")
public class demo{
@PostMapping("test1")
public JsonObject test1() {
...
return jo;
}
}
4.2 Feign Client
@FeignClient(
name = "demo",
url = "http://localhost:8080",
configuration = DemoConfiguration.class
)
@RequestMapping(value = "/demo")
public interface DemoFeignClient {
@RequestMapping(value = "/test1", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE)
Info info();
}
如果 @RequestMapping注解被用在FeignClient类上，当像如下代码请求/demo/test1时，注意有Accept header：
Content-Type:application/json
Accept:application/json
POST http://localhost:8080/demo/test1
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:8080/demo/test1
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 = "demo",
url = "http://localhost:8080",
configuration = DemoConfiguration.class
)
public interface DemoFeignClient {
@RequestMapping(value = "/demo/test1", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE)
Info info();
}
5. Feign请求超时问题
Hystrix默认的超时时间是1秒，如果超过这个时间尚未响应，将会进入fallback代码。而首次请求往往会比较慢（因为Spring的懒加载机制，要实例化一些类），这个响应时间可能就大于1秒了
解决方案有如下三种：
5.1
hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds: 5000
该配置是让Hystrix的超时时间改为5秒
5.2
hystrix.command.default.execution.timeout.enabled: false
该配置，用于禁用Hystrix的超时时间
5.3
feign.hystrix.enabled: false
该配置，用于禁用feign的hystrix。该做法除非一些特殊场景，不推荐使用。