Spring Cloud Feign Client 实现MultipartFile上传文件功能

项目是用Spring Cloud搭的微服务，使用了eureka，FeignClient。今天在做上传文件功能时，直接使用FeignClient去远程调用注册中心上的上传文件接口，一直报错。
解决方案：
加入maven依赖<dependency>
<groupId>io.github.openfeign.form</groupId>
<artifactId>feign-form-spring</artifactId>
<version>3.2.2</version>
</dependency>
<dependency>
<groupId>io.github.openfeign.form</groupId>
<artifactId>feign-form</artifactId>
<version>3.2.2</version>
</dependency>FeignClient接口里方法参数是文件类型的要用@RequestPart注解，且要设置ContentType为multipart/form-data

@FeignClient(value = "quote-service/api/attendance", configuration = IFeignAttendanceService.MultipartSupportConfig.class)
public interface IFeignAttendanceService {

    @PostMapping(value = "uploadFile", consumes = MediaType.MULTIPART_FORM_DATA )
    Object uploadFile(@RequestPart(value = "file") MultipartFile file, @RequestParam("prefixName") String prefixName);

    @Configuration
class MultipartSupportConfig {
@Bean
public Encoder feignFormEncoder() {
return new SpringFormEncoder();
}
}
}

上面的MultipartSupportConfig 类也可以单独作为一个类，这里为了省事，用了内部类。
通过测试后发现，当我的接口参数使用实体类接收时，会抛如下异常：2018-04-04 09:52:13.410 [http-nio-8720-exec-1] ERROR o.a.c.c.C.[.[localhost].[/].[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is feign.codec.EncodeException: class cn.erongcai.hrplatform.entity.Quote is not a type supported by this encoder.] with root cause
feign.codec.EncodeException: class cn.erongcai.hrplatform.entity.Quote is not a type supported by this encoder.
at feign.codec.Encoder$Default.encode(Encoder.java:90)
at feign.form.FormEncoder.encode(FormEncoder.java:87)
at feign.form.spring.SpringFormEncoder.encode(SpringFormEncoder.java:64)
at feign.ReflectiveFeign$BuildEncodedTemplateFromArgs.resolve(ReflectiveFeign.java:350)
at feign.ReflectiveFeign$BuildTemplateByResolvingArgs.create(ReflectiveFeign.java:213)
at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:72)
at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103)
at com.sun.proxy.$Proxy96.saveQuote(Unknown Source)
at cn.erongcai.hrplatform.web.FeignQuoteController.saveQuote(FeignQuoteController.java:45)
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:205)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:105)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)为什么会抛异常呢，查看SpringFormEncoder类的源码：public class SpringFormEncoder extends FormEncoder
{

public SpringFormEncoder()
{
this(((Encoder) (new feign.codec.Encoder.Default())));
}

public SpringFormEncoder(Encoder delegate)
{
super(delegate);//调用父类的构造方法
MultipartFormContentProcessor processor = (MultipartFormContentProcessor)getContentProcessor(ContentType.MULTIPART);
processor.addWriter(new SpringSingleMultipartFileWriter());
processor.addWriter(new SpringManyMultipartFilesWriter());
}

public void encode(Object object, Type bodyType, RequestTemplate template)
throws EncodeException
{
if(!bodyType.equals(org/springframework/web/multipart/MultipartFile))
{
super.encode(object, bodyType, template);//调用FormEncoder对应方法
return;
} else
{
MultipartFile file = (MultipartFile)object;
java.util.Map data = Collections.singletonMap(file.getName(), object);
super.encode(data, MAP_STRING_WILDCARD, template);
return;
}
}
}我们可以发现SpringFormEncoder的encode方法当传送的对象不是MultipartFile的时候，就会调用super.encode， 也就是FormEncoder的encode方法。
FormEncoder类的部分源码：
public FormEncoder()
{
this(((Encoder) (new feign.codec.Encoder.Default())));
}

public FormEncoder(Encoder delegate)
{
_flddelegate = delegate;
List list = Arrays.asList(new ContentProcessor[] {
new MultipartFormContentProcessor(delegate), new UrlencodedFormContentProcessor()
});
processors = new HashMap(list.size(), 1.0F);
ContentProcessor processor;
for(Iterator iterator = list.iterator(); iterator.hasNext(); processors.put(processor.getSupportedContentType(), processor))
processor = (ContentProcessor)iterator.next();

}

public void encode(Object object, Type bodyType, RequestTemplate template)
throws EncodeException
{
String contentTypeValue = getContentTypeValue(template.headers());//这里会去到@PostMapping中consumes的值，所以参数需要传对象时指定一下consumes
ContentType contentType = ContentType.of(contentTypeValue);//为啥指定consumes，是因为不指定就是application/x-www-form-urlencoded，而且processors中也包含，为啥包含见FormEncoder的构造函数
if(!MAP_STRING_WILDCARD.equals(bodyType) || !processors.containsKey(contentType))
{
_flddelegate.encode(object, bodyType, template);//_flddelegate是啥呢，是SpringFormEncoder传递过来，也就是new Encoder.Default()
return;
}
Charset charset = getCharset(contentTypeValue);
Map data = (Map)object;
try
{
((ContentProcessor)processors.get(contentType)).process(template, charset, data);
}
catch(Exception ex)
{
throw new EncodeException(ex.getMessage());
}
}FormEncoderr的encode方法当传送的对象是json格式的字符串的时候，就会调用 _flddelegate.encode，即Encoder.Default的encode方法，而这个Encoder.Default的encode方法判断传送的类型不是String或者byte[]，就会抛异常public interface Encoder
{
public static class Default
implements Encoder
{

public void encode(Object object, Type bodyType, RequestTemplate template)
{
if(bodyType == java/lang/String)
template.body(object.toString());
else
if(bodyType == [B)
template.body((byte[])(byte[])object, null);
else
if(object != null)//当我们用对象传递参数的时候，会走这里
throw new EncodeException(String.format("%s is not a type supported by this encoder.", new Object[] {
object.getClass()
}));
}

public Default()
{
}
}

public abstract void encode(Object obj, Type type, RequestTemplate requesttemplate)
throws EncodeException;

public static final Type MAP_STRING_WILDCARD = Util.MAP_STRING_WILDCARD;

}因为我的项目中有很多接口用实体类作为接收参数的，所以上述解决方案无法满足我的要求。所以只能继续各种百度、各种谷歌，终于找到了合适的解决方案。
解决方案一：如果引用该配置类的FeignClient中，没有使用实体类作为参数的接口，则去掉配置类上的注解@Configuration就可以了，去掉注解@Configuration之后，该配置就只对通过configuration属性引用该配置的FeignClient起作用。
解决方案二：