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        这里我的业务场景是：在请求头中获取服务端登录时传给客户端的token，并且客户端将token放在请求头中。以至于我需要在参数传递上传入HttpServletRequest。如果你非要向我一样传入HttpServletRequest对象那么就往下看，当然你如果可以改成其他参数传递就不需要往下看了。

使用Feign所需要的必需知识别忘记：

1、需要在调用方以及被调用方以及Feign接口模块引入依赖

2、被调用方与调用方的主启动类均需要加上@EnableFeignClients注解

3、被调用方的注解后面还需要加扫描路径，对于我本人项目则是@EnableFeignClients(basePackages = "com.chf")

4、被调用方的控制层(Controller)的方法需要是public。因为写在Feign接口中的方法就是默认的public static final。所以说两个的访问权限修饰符必须是一致的。

5、将被调用方的方法copy到Feign接口中，这里需要注意三点：

一、在@RequestMapper/REST风格的请求路径中需要被调用方的全路径名。

二、Feign接口需要两个注解：@Component以及@FeignClient。

三、@FeignClient注解中需要加上被调用方的服务名称（"spring:application:name"）

feign.codec.EncodeException: Could not write JSON: getInputStream() has already been called for this request; nested exception is com.fasterxml.jackson.databind.JsonMappingException: getInputStream() has already been called for this request (through reference chain: org.apache.catalina.connector.RequestFacade["reader"])
	at feign.ReflectiveFeign$BuildEncodedTemplateFromArgs.resolve(ReflectiveFeign.java:376)
	at feign.ReflectiveFeign$BuildTemplateByResolvingArgs.create(ReflectiveFeign.java:224)
	at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:75)
	at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103)
	at com.sun.proxy.$Proxy81.concertCount(Unknown Source)
	at com.chf.service.impl.ApiEChartsServiceImpl.ticketCount(ApiEChartsServiceImpl.java:25)
	at com.chf.controller.api.ApiEChartsController.ticketCount(ApiEChartsController.java:25)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1579)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: getInputStream() has already been called for this request; nested exception is com.fasterxml.jackson.databind.JsonMappingException: getInputStream() has already been called for this request (through reference chain: org.apache.catalina.connector.RequestFacade["reader"])
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:296)
	at org.springframework.http.converter.AbstractGenericHttpMessageConverter.writeInternal(AbstractGenericHttpMessageConverter.java:113)
	at org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:227)
	at org.springframework.cloud.openfeign.support.SpringEncoder.encode(SpringEncoder.java:114)
	at feign.ReflectiveFeign$BuildEncodedTemplateFromArgs.resolve(ReflectiveFeign.java:372)
	... 56 more
Caused by: com.fasterxml.jackson.databind.JsonMappingException: getInputStream() has already been called for this request (through reference chain: org.apache.catalina.connector.RequestFacade["reader"])
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:394)
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:353)
	at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:316)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:729)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
	at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1433)
	at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:921)
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:287)
	... 60 more
Caused by: java.lang.IllegalStateException: getInputStream() has already been called for this request
	at org.apache.catalina.connector.Request.getReader(Request.java:1208)
	at org.apache.catalina.connector.RequestFacade.getReader(RequestFacade.java:504)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:688)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:721)
	... 66 more

        报这个错误的原因主要是：Feign没有接受HttpServletRequest参数。以下三点是处理这个问题的解决办法。第一：在Feign模块中写一个配置类实现RequestInterceptor重写apply()方法。

二、修改Feign接口中的两处地方。三、在调用方调用Feign接口地方改为请求头中的参数。

@Component
public class FeignConfig implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate requestTemplate) {
        ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = attributes.getRequest();
        requestTemplate.header("token",request.getHeader("token"));
    }
}

@Component
// 第一处更改的位置：加上configuration
@FeignClient(value = "service:application:name",configuration = FeignConfig.class)
public interface FeignClient {

    @GetMapping("全路径名")
    // 第二处更改的位置：加上@RequestHeader注解并且带上需要的请求头类型
    Integer count(@RequestHeader("token") String token);
}

@Service
public class AServiceImpl implements AService {

    @Autowired
    private FeignClient feignClient;

    @Override
    public Integer personCount(HttpServletRequest request) {
        String token = request.getHeader("token");
        return feignClient.count(token);
    }
}