使用Feign扩展包实现微服务间文件上传

在Spring Cloud 的Feign组件中并不支持文件的传输，会出现这样的错误提示：

feign.codec.EncodeException: class [Lorg.springframework.web.multipart.MultipartFile; is not a type supported by this encoder.
 at feign.codec.Encoder$Default.encode(Encoder.java:90) ~[feign-core-9.5.1.jar:na]
 at feign.form.FormEncoder.encode(FormEncoder.java:87) ~[feign-form-3.3.0.jar:3.3.0]
 at feign.form.spring.SpringFormEncoder.encode(SpringFormEncoder.java:64) ~[feign-form-spring-3.3.0.jar:3.3.0]

但是我们可以通过使用Feign的扩展包实现这个功能。

一. 示例介绍

我们调用feign_upload_second的上传文件接口上传文件，feign_upload_second内部使用feign调用feign_upload_first实现文件上传。

二 、单文件上传

2.1 feign_upload_first服务提供者

文件上传的服务提供者接口比较简单，如下所示：

@SpringBootApplication
public class FeignUploadFirstApplication {
@RestController
public class UploadController {

@RequestMapping(value = "/uploadFile",method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
 public String handleFileUpload(@RequestPart(value = "file") MultipartFile file) {
  return file.getOriginalFilename();
 }
}
public static void main(String[] args) {
 SpringApplication.run(FeignUploadFirstApplication.class, args);
}
}

2.2 feign_upload_second服务消费者

增加扩展包依赖

<dependency>
  <groupId>io.github.openfeign.form</groupId>
  <artifactId>feign-form</artifactId>
  <version>3.3.0</version>
 </dependency>
 <dependency>
  <groupId>io.github.openfeign.form</groupId>
  <artifactId>feign-form-spring</artifactId>
  <version>3.3.0</version>
 </dependency>
 <dependency>
  <groupId>commons-fileupload</groupId>
  <artifactId>commons-fileupload</artifactId>
  <version>1.3.3</version>
</dependency>

新增feign实现文件上传的配置类

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

feign远程调用接口

@FeignClient(name = "file",url = "http://localhost:8100",configuration = FeignSupportConfig.class)
public interface UploadService {
@RequestMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
String handleFileUpload(@RequestPart(value = "file") MultipartFile file);
}

上传文件接口

@RestController
public class UploadController {
@Autowired
UploadService uploadService;

@RequestMapping(value = "/uploadFile",method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public String handleFileUpload(@RequestPart(value = "file") MultipartFile file) {
 return uploadService.handleFileUpload(file);
}
}

2.3 测试

使用postman进行测试，可以正常上传文件

三、多文件上传

既然单个文件可以上传，那么多文件应该也没问题吧，我们对上面的代码进行修改

3.1 feign_upload_first服务提供者

文件上传的服务提供者接口比较简单，如下所示：

@SpringBootApplication
public class FeignUploadFirstApplication {
@RestController
public class UploadController {

@RequestMapping(value = "/uploadFile",method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
 public String handleFileUpload(@RequestPart(value = "file") MultipartFile file) {
  return file.getOriginalFilename();
 }

@RequestMapping(value = "/uploadFile2",method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
 public String handleFileUpload(@RequestPart(value = "file") MultipartFile[] file) {
  String fileName = "";
  for(MultipartFile f : file){
   fileName += f.getOriginalFilename()+"---";
  }
  return fileName;
 }
}
public static void main(String[] args) {
 SpringApplication.run(FeignUploadFirstApplication.class, args);
}
}

3.2 feign_upload_second服务消费者

feign远程调用接口

@FeignClient(name = "file",url = "http://localhost:8100",configuration = FeignSupportConfig.class)
public interface UploadService {
@RequestMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
String handleFileUpload(@RequestPart(value = "file") MultipartFile file);

@RequestMapping(value = "/uploadFile2", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
String handleFileUpload(@RequestPart(value = "file") MultipartFile[] file);
}

上传文件接口

@RestController
public class UploadController {
@Autowired
UploadService uploadService;

@RequestMapping(value = "/uploadFile",method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public String handleFileUpload(@RequestPart(value = "file") MultipartFile file) {
 return uploadService.handleFileUpload(file);
}

@RequestMapping(value = "/uploadFile2",method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public String handleFileUpload2(@RequestPart(value = "file") MultipartFile[] file) {
 return uploadService.handleFileUpload(file);
}
}

3.3 测试

经过测试发现，无法上传多个文件。经过检查，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

public class SpringManyMultipartFilesWriter extends AbstractWriter {
private final SpringSingleMultipartFileWriter fileWriter = new SpringSingleMultipartFileWriter();

public SpringManyMultipartFilesWriter() {
}

public void write(Output output, String boundary, String key, Object value) throws Exception {
 if (value instanceof MultipartFile[]) {
  MultipartFile[] files = (MultipartFile[])((MultipartFile[])value);
  MultipartFile[] var6 = files;
  int var7 = files.length;

for(int var8 = 0; var8 < var7; ++var8) {
   MultipartFile file = var6[var8];
   this.fileWriter.write(output, boundary, key, file);
  }
 } else if (value instanceof Iterable) {
  Iterable<?> iterable = (Iterable)value;
  Iterator var11 = iterable.iterator();

while(var11.hasNext()) {
   Object file = var11.next();
   this.fileWriter.write(output, boundary, key, file);
  }
 }

}

public boolean isApplicable(Object value) {
 if (value == null) {
  return false;
 } else if (value instanceof MultipartFile[]) {
  return true;
 } else {
  if (value instanceof Iterable) {
   Iterable<?> iterable = (Iterable)value;
   Iterator<?> iterator = iterable.iterator();
   if (iterator.hasNext() && iterator.next() instanceof MultipartFile) {
    return true;
   }
  }

return false;
 }
}
}

SpringFormEncoder源码

public class SpringFormEncoder extends FormEncoder {
public SpringFormEncoder() {
 this(new Default());
}

public SpringFormEncoder(Encoder delegate) {
 super(delegate);
 MultipartFormContentProcessor processor = (MultipartFormContentProcessor)this.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(MultipartFile.class)) {
  super.encode(object, bodyType, template);
 } else {
  MultipartFile file = (MultipartFile)object;
  Map<String, Object> data = Collections.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，底层有对数组的支持但上层却缺少了相应判断。那么我们可以自己去扩展FormEncoder，仿照SpringFormEncoder源码，只修改encode方法。

3.3 扩展FormEncoder支持多文件上传

扩展FormEncoder,命名为FeignSpringFormEncoder

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

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

MultipartFormContentProcessor processor = (MultipartFormContentProcessor) getContentProcessor(ContentType.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)) {
  MultipartFile file = (MultipartFile) object;
  Map data = Collections.singletonMap(file.getName(), object);
  super.encode(data, MAP_STRING_WILDCARD, template);
  return;
 } else if (bodyType.equals(MultipartFile[].class)) {
  MultipartFile[] file = (MultipartFile[]) object;
  if(file != null) {
   Map data = Collections.singletonMap(file.length == 0 ? "" : file[0].getName(), object);
   super.encode(data, MAP_STRING_WILDCARD, template);
   return;
  }
 }
 super.encode(object, bodyType, template);
}
}

注册配置类

@Configuration
public class FeignSupportConfig {
@Bean
public Encoder feignFormEncoder() {
 return new FeignSpringFormEncoder();
}
}

经过测试可以上传多个文件。

来源：https://blog.csdn.net/AaronSimon/article/details/82710938