Spring Cloud中FeignClient添加上传文件功能

项目概况：Spring Cloud搭的微服务，使用了eureka，FeignClient，现在遇到FeignClient调用接口时不支持上传文件，

百度到两种方案，一种是使用feign-form和feign-form-spring库来做，源码地址：https://github.com/OpenFeign/feign-form。

具体的使用方法是加入maven依赖

        
            io.github.openfeign.form
            feign-form-spring
            3.2.2
        
        
            io.github.openfeign.form
            feign-form
            3.2.2
        

注入SpringFormEncoder类

    @Bean
    @Primary
    @Scope("prototype")
    public Encoder multipartFormEncoder() {
        return new SpringFormEncoder();
    }

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

    @ResponseBody
    @RequestMapping(value = "/ctstestcase/updateTestCase", method = {RequestMethod.POST}, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    Map updateTestCase(@RequestParam("testcaseId") String testcaseId,
            @RequestParam("name") String name, @RequestParam("assignId") String assignId,
            @RequestParam("areaId") String areaId, @RequestParam("state") Integer state,
            @RequestParam("iterationId") String iterationId,@RequestParam("priority") Integer priority,
            @RequestParam("moduleId") String moduleId,  @RequestParam("executionType") Integer executionType,
            @RequestParam("summary") String summary, @RequestParam("tcsteps") String tcsteps,
            @RequestParam("relations") String relations,@RequestParam("attachments") String attachments,
            @RequestPart("files") MultipartFile[] files);

但遇到一个问题，就是不支持文件数组类型，我看了源码，发现源码里底层是有对MultipartFile[]类型的支持的，源码中有个类叫SpringManyMultipartFilesWriter，是专门针对文件数组类型进行操作的，但是配置到项目里的SpringFormEncoder类里却没有对文件数组类型的判断，以致不能支持文件数组的上传.。

SpringManyMultipartFilesWriter源码：

@FieldDefaults(level = PRIVATE, makeFinal = true)
public class SpringManyMultipartFilesWriter extends AbstractWriter {

  SpringSingleMultipartFileWriter fileWriter = new SpringSingleMultipartFileWriter();

  @Override
  public void write (Output output, String boundary, String key, Object value) throws Exception {
    if (value instanceof MultipartFile[]) {
      val files = (MultipartFile[]) value;
      for (val file : files) {
        fileWriter.write(output, boundary, key, file);
      }
    } else if (value instanceof Iterable) {
      val iterable = (Iterable) value;
      for (val file : iterable) {
        fileWriter.write(output, boundary, key, file);
      }
    }
  }

  @Override
  public boolean isApplicable (Object value) {
    if (value == null) {
      return false;
    }
    if (value instanceof MultipartFile[]) {
      return true;
    }
    if (value instanceof Iterable) {
      val iterable = (Iterable) value;
      val iterator = iterable.iterator();
      if (iterator.hasNext() && iterator.next() instanceof MultipartFile) {
        return true;
      }
    }
    return false;
  }

SpringFormEncoder源码：

public class SpringFormEncoder extends FormEncoder {

  /**
   * Constructor with the default Feign's encoder as a delegate.
   */
  public SpringFormEncoder () {
    this(new Encoder.Default());
  }

  /**
   * Constructor with specified delegate encoder.
   *
   * @param delegate  delegate encoder, if this encoder couldn't encode object.
   */
  public SpringFormEncoder (Encoder delegate) {
    super(delegate);

    val processor = (MultipartFormContentProcessor) getContentProcessor(MULTIPART);
    processor.addWriter(new SpringSingleMultipartFileWriter());
    processor.addWriter(new SpringManyMultipartFilesWriter());
  }

  @Override
  public void encode (Object object, Type bodyType, RequestTemplate template) throws EncodeException {
    if (!bodyType.equals(MultipartFile.class)) {
      super.encode(object, bodyType, template);
      return;
    }

    val file = (MultipartFile) object;
    val data = singletonMap(file.getName(), object);
    super.encode(data, MAP_STRING_WILDCARD, template);
  }
}

从上面SpringFormEncoder的源码上可以看到SpringFormEncoder类构造时把SpringManyMultipartFilesWriter实例添加到了处理器列表里了，但是在encode方法里又只判断了MultipartFile类型，没有判断数组类型，这就比较奇怪了，底层有对数组的支持但上层却缺少了相应判断，而且在源码里的test包里也没有对文件数组类型的测试，难道只是encode方法里漏掉了？还是说那个文件数组的支持有问题？所以encode方法里才没有加入对其的判断？

于是我先试着对encode方法进行扩展加入对文件数组的判断，应该就可以支持文件数组的上传了，于是把SpringFormEncoder类源码复制出来重命名为FeignSpringFormEncoder,源码如下：

public class FeignSpringFormEncoder extends FormEncoder {

    /**
     * Constructor with the default Feign's encoder as a delegate.
     */
    public FeignSpringFormEncoder() {
        this(new Encoder.Default());
    }


    /**
     * Constructor with specified delegate encoder.
     *
     * @param delegate delegate encoder, if this encoder couldn't encode object.
     */
    public FeignSpringFormEncoder(Encoder delegate) {
        super(delegate);

        val processor = (MultipartFormContentProcessor) getContentProcessor(MULTIPART);
        processor.addWriter(new SpringSingleMultipartFileWriter());
        processor.addWriter(new SpringManyMultipartFilesWriter());
    }


    @Override
    public void encode(Object object, Type bodyType, RequestTemplate template) throws EncodeException {
        if (bodyType.equals(MultipartFile.class)) {
            val file = (MultipartFile) object;
            val data = singletonMap(file.getName(), object);
            super.encode(data, MAP_STRING_WILDCARD, template);
            return;
        } else if (bodyType.equals(MultipartFile[].class)) {
            val file = (MultipartFile[]) object;
            if(file != null) {
                val data = singletonMap(file.length == 0 ? "" : file[0].getName(), object);
                super.encode(data, MAP_STRING_WILDCARD, template);
                return;
            }
        }
        super.encode(object, bodyType, template);
    }
}

经过测试，已经可以支持文件数组了，完美解决。

 这里再顺便说一下当时还百度到另一个解决文件上传的方案，这个方案就不细说了，直接上我用到的那个开源代码的地址：https://github.com/pcan/feign-client-test

这个我试过也是可以解决文件上传问题的，但问题是FeignClient不能用SpringMVC的注解，得用Feign自带的注解，也因此我才扩展了第一种方法来做的文件上传功能。