Spring Cloud中FeignClient实现文件上传功能

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。

具体的使用方法是加入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>

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<String, Object> 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

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。

来源：https://blog.csdn.net/ytzzh0726/article/details/79467843