SpringCloud+Feign环境下文件上传与form-data同时存在的解决办法(2)

书接上文。

上文中描述了如何在 SpringCloud+Feign环境下上传文件与form-data同时存在的解决办法，实践证明基本可行，但却会引入其他问题。

主要导致的后果是：

1. 无法与普通Feign方法并存

2. 几率性（不确定条件下）导致其他form-data类型参数无法识别，无法正常工作，错误信息大致如下：

org.springframework.web.multipart.support.MissingServletRequestPartException: Required request part 'file' is not present

分析原因发现是Feign的Encoder体系中缺乏对应的配置从而无法工作；但将这些Encoder一一补上却过于困难，因此，决定换一个思路，使用Spring技术解决该问题。

该问题的本质是controller层传参时参数的编解码问题，因此，应该属于HttpMessageConverter范畴的事情，这参考SpringEncoder的代码即可得知。

最终，解决方案如下：

1. 去掉依赖，因为不再需要

             <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>

2. 去掉类  FeignSpringFormEncoder ，不再需要

3. 注解  RequestPartParam 、类  RequestPartParamParameterProcessor 以及 bean 的定义均与上文保持一致

4. 参考类  FormHttpMessageConverter  添加类  LinkedHashMapFormHttpMessageConverter  ，并注意使用 @Conponent注解进行Spring托管。代码如下：

 import org.springframework.core.io.Resource;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.HttpOutputMessage;
 import org.springframework.http.MediaType;
 import org.springframework.http.StreamingHttpOutputMessage;
 import org.springframework.http.converter.AbstractHttpMessageConverter;
 import org.springframework.http.converter.ByteArrayHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.HttpMessageNotReadableException;
 import org.springframework.http.converter.HttpMessageNotWritableException;
 import org.springframework.http.converter.ResourceHttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.stereotype.Component;
 import org.springframework.util.Assert;
 import org.springframework.util.MimeTypeUtils;
 import org.springframework.web.multipart.MultipartFile;
 
 import javax.mail.internet.MimeUtility;
 
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.UnsupportedEncodingException;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
 /**
  * 参考 FormHttpMessageConverter
  */
 @Component
 public class LinkedHashMapFormHttpMessageConverter implements HttpMessageConverter<LinkedHashMap<String, ?>> {
 
     public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
 
     private List<MediaType> supportedMediaTypes = new ArrayList<MediaType>();
 
     private List<HttpMessageConverter<?>> partConverters = new ArrayList<HttpMessageConverter<?>>();
 
     private Charset charset = DEFAULT_CHARSET;
 
     private Charset multipartCharset;
 
     public LinkedHashMapFormHttpMessageConverter() {
         this.supportedMediaTypes.add(MediaType.MULTIPART_FORM_DATA);
 
         StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
         stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316
 
         this.partConverters.add(new ByteArrayHttpMessageConverter());
         this.partConverters.add(stringHttpMessageConverter);
         this.partConverters.add(new ResourceHttpMessageConverter());
 
         MultipartFileHttpMessageConverter multipartFileHttpMessageConverter = new MultipartFileHttpMessageConverter();
         this.partConverters.add(multipartFileHttpMessageConverter);
 
         applyDefaultCharset();
     }
 
     @Override
     public List<MediaType> getSupportedMediaTypes() {
         return Collections.unmodifiableList(this.supportedMediaTypes);
     }
 
     public void setPartConverters(List<HttpMessageConverter<?>> partConverters) {
         Assert.notEmpty(partConverters, "'partConverters' must not be empty");
         this.partConverters = partConverters;
     }
 
     public void addPartConverter(HttpMessageConverter<?> partConverter) {
         Assert.notNull(partConverter, "'partConverter' must not be null");
         this.partConverters.add(partConverter);
     }
 
     public void setCharset(Charset charset) {
         if (charset != this.charset) {
             this.charset = (charset != null ? charset : DEFAULT_CHARSET);
             applyDefaultCharset();
         }
     }
 
     private void applyDefaultCharset() {
         for (HttpMessageConverter<?> candidate : this.partConverters) {
             if (candidate instanceof AbstractHttpMessageConverter) {
                 AbstractHttpMessageConverter<?> converter = (AbstractHttpMessageConverter<?>) candidate;
                 // Only override default charset if the converter operates with a charset to begin with...
                 if (converter.getDefaultCharset() != null) {
                     converter.setDefaultCharset(this.charset);
                 }
             }
         }
     }
 
     public void setMultipartCharset(Charset charset) {
         this.multipartCharset = charset;
     }
 
     @Override
     public boolean canRead(Class<?> clazz, MediaType mediaType) {
         return false;
     }
 
     @Override
     public boolean canWrite(Class<?> clazz, MediaType mediaType) {
         if (!LinkedHashMap.class.isAssignableFrom(clazz)) {
             return false;
         }
         if (mediaType == null || MediaType.ALL.equals(mediaType)) {
             return false;
         }
         for (MediaType supportedMediaType : getSupportedMediaTypes()) {
             if (supportedMediaType.isCompatibleWith(mediaType)) {
                 return true;
             }
         }
         return false;
     }
 
     @Override
     public LinkedHashMap<String, String> read(Class<? extends LinkedHashMap<String, ?>> clazz,
                                               HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
         throw new HttpMessageNotReadableException("Not supportted for read.");
     }
 
     @Override
     @SuppressWarnings("unchecked")
     public void write(LinkedHashMap<String, ?> map, MediaType contentType, HttpOutputMessage outputMessage)
             throws IOException, HttpMessageNotWritableException {
 
         writeMultipart((LinkedHashMap<String, Object>) map, outputMessage);
     }
 
     private void writeMultipart(final LinkedHashMap<String, Object> parts, HttpOutputMessage outputMessage) throws IOException {
         final byte[] boundary = generateMultipartBoundary();
         Map<String, String> parameters = Collections.singletonMap("boundary", new String(boundary, "US-ASCII"));
 
         MediaType contentType = new MediaType(MediaType.MULTIPART_FORM_DATA, parameters);
         HttpHeaders headers = outputMessage.getHeaders();
         headers.setContentType(contentType);
 
         if (outputMessage instanceof StreamingHttpOutputMessage) {
             StreamingHttpOutputMessage streamingOutputMessage = (StreamingHttpOutputMessage) outputMessage;
             streamingOutputMessage.setBody(new StreamingHttpOutputMessage.Body() {
                 @Override
                 public void writeTo(OutputStream outputStream) throws IOException {
                     writeParts(outputStream, parts, boundary);
                     writeEnd(outputStream, boundary);
                 }
             });
         }
         else {
             writeParts(outputMessage.getBody(), parts, boundary);
             writeEnd(outputMessage.getBody(), boundary);
         }
     }
 
     private void writeParts(OutputStream os, LinkedHashMap<String, Object> parts, byte[] boundary) throws IOException {
         for (Map.Entry<String, Object> entry : parts.entrySet()) {
             String name = entry.getKey();
             Object part = entry.getValue();
             if (part != null) {
                 writeBoundary(os, boundary);
                 writePart(name, getHttpEntity(part), os);
                 writeNewLine(os);
             }
         }
     }
 
     @SuppressWarnings("unchecked")
     private void writePart(String name, HttpEntity<?> partEntity, OutputStream os) throws IOException {
         Object partBody = partEntity.getBody();
         Class<?> partType = partBody.getClass();
         HttpHeaders partHeaders = partEntity.getHeaders();
         MediaType partContentType = partHeaders.getContentType();
         for (HttpMessageConverter<?> messageConverter : this.partConverters) {
             if (messageConverter.canWrite(partType, partContentType)) {
                 HttpOutputMessage multipartMessage = new MultipartHttpOutputMessage(os);
                 multipartMessage.getHeaders().setContentDispositionFormData(name, getFilename(partBody));
                 if (!partHeaders.isEmpty()) {
                     multipartMessage.getHeaders().putAll(partHeaders);
                 }
                 ((HttpMessageConverter<Object>) messageConverter).write(partBody, partContentType, multipartMessage);
                 return;
             }
         }
         throw new HttpMessageNotWritableException("Could not write request: no suitable HttpMessageConverter " +
                 "found for request type [" + partType.getName() + "]");
     }
 
     protected byte[] generateMultipartBoundary() {
         return MimeTypeUtils.generateMultipartBoundary();
     }
 
     protected HttpEntity<?> getHttpEntity(Object part) {
         return (part instanceof HttpEntity ? (HttpEntity<?>) part : new HttpEntity<Object>(part));
     }
 
     protected String getFilename(Object part) {
         if (part instanceof Resource) {
             Resource resource = (Resource) part;
             String filename = resource.getFilename();
             if (filename != null && this.multipartCharset != null) {
                 filename = MimeDelegate.encode(filename, this.multipartCharset.name());
             }
             return filename;
         } else if (part instanceof MultipartFile) {
             MultipartFile multipartFile = (MultipartFile) part;
             String filename = multipartFile.getName();
             if (filename == null || filename.isEmpty()) {
                 filename = multipartFile.getOriginalFilename();
             }
             return filename;
         }
         else {
             return null;
         }
     }
 
     private void writeBoundary(OutputStream os, byte[] boundary) throws IOException {
         os.write('-');
         os.write('-');
         os.write(boundary);
         writeNewLine(os);
     }
 
     private static void writeEnd(OutputStream os, byte[] boundary) throws IOException {
         os.write('-');
         os.write('-');
         os.write(boundary);
         os.write('-');
         os.write('-');
         writeNewLine(os);
     }
 
     private static void writeNewLine(OutputStream os) throws IOException {
         os.write('\r');
         os.write('\n');
     }
 
     private static class MultipartHttpOutputMessage implements HttpOutputMessage {
 
         private final OutputStream outputStream;
 
         private final HttpHeaders headers = new HttpHeaders();
 
         private boolean headersWritten = false;
 
         public MultipartHttpOutputMessage(OutputStream outputStream) {
             this.outputStream = outputStream;
         }
 
         @Override
         public HttpHeaders getHeaders() {
             return (this.headersWritten ? HttpHeaders.readOnlyHttpHeaders(this.headers) : this.headers);
         }
 
         @Override
         public OutputStream getBody() throws IOException {
             writeHeaders();
             return this.outputStream;
         }
 
         private void writeHeaders() throws IOException {
             if (!this.headersWritten) {
                 for (Map.Entry<String, List<String>> entry : this.headers.entrySet()) {
                     byte[] headerName = getAsciiBytes(entry.getKey());
                     for (String headerValueString : entry.getValue()) {
                         byte[] headerValue = getAsciiBytes(headerValueString);
                         this.outputStream.write(headerName);
                         this.outputStream.write(':');
                         this.outputStream.write(' ');
                         this.outputStream.write(headerValue);
                         writeNewLine(this.outputStream);
                     }
                 }
                 writeNewLine(this.outputStream);
                 this.headersWritten = true;
             }
         }
 
         private byte[] getAsciiBytes(String name) {
             try {
                 return name.getBytes("US-ASCII");
             }
             catch (UnsupportedEncodingException ex) {
                 // Should not happen - US-ASCII is always supported.
                 throw new IllegalStateException(ex);
             }
         }
     }
 
     private static class MimeDelegate {
 
         public static String encode(String value, String charset) {
             try {
                 return MimeUtility.encodeText(value, charset, null);
             }
             catch (UnsupportedEncodingException ex) {
                 throw new IllegalStateException(ex);
             }
         }
     }
 }

5. 参考类  ResourceHttpMessageConverter  添加类  MultipartFileHttpMessageConverter ，代码如下：

 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.HttpOutputMessage;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.AbstractHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageNotReadableException;
 import org.springframework.http.converter.HttpMessageNotWritableException;
 import org.springframework.util.StreamUtils;
 import org.springframework.web.multipart.MultipartFile;
 
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 
 public class MultipartFileHttpMessageConverter extends AbstractHttpMessageConverter<MultipartFile> {
 
     public MultipartFileHttpMessageConverter() {
         super(MediaType.APPLICATION_OCTET_STREAM);
     }
 
     @Override
     protected boolean supports(Class<?> clazz) {
         return MultipartFile.class.isAssignableFrom(clazz);
     }
 
     @Override
     protected MultipartFile readInternal(Class<? extends MultipartFile> clazz, HttpInputMessage inputMessage)
             throws IOException, HttpMessageNotReadableException {
         throw new HttpMessageNotReadableException("Not supportted for read.");
     }
 
     @Override
     protected MediaType getDefaultContentType(MultipartFile multipartFile) {
         try {
             String contentType = multipartFile.getContentType();
             MediaType mediaType = MediaType.valueOf(contentType);
             if (mediaType != null) {
                 return mediaType;
             }
         } catch (Exception ex) {
         }
         return MediaType.APPLICATION_OCTET_STREAM;
     }
 
     @Override
     protected Long getContentLength(MultipartFile multipartFile, MediaType contentType) throws IOException {
         long contentLength = multipartFile.getSize();
         return (contentLength < 0 ? null : contentLength);
     }
 
     @Override
     protected void writeInternal(MultipartFile multipartFile, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
         writeContent(multipartFile, outputMessage);
     }
 
     protected void writeContent(MultipartFile multipartFile, HttpOutputMessage outputMessage)
             throws IOException, HttpMessageNotWritableException {
         try {
             InputStream in = multipartFile.getInputStream();
             try {
                 StreamUtils.copy(in, outputMessage.getBody());
             }
             catch (NullPointerException ex) {
                 // ignore, see SPR-13620
             }
             finally {
                 try {
                     in.close();
                 }
                 catch (Throwable ex) {
                     // ignore, see SPR-12999
                 }
             }
         }
         catch (FileNotFoundException ex) {
             // ignore, see SPR-12999
         }
     }
 
 }

按照上述配置即可工作，但需要严格注意：

由于使用 LinkedHashMapFormHttpMessageConverter 的原因，会导致：

当某次http请求的参数或者返回值中包含 LinkedHashMap 且其请求的MediaType兼容 MULTIPART_FORM_DATA 时，该次参数或者返回值会错误的被 LinkedHashMapFormHttpMessageConverter 处理，但此时很显然是不正确的处理方式。

对应的办法：避开该情况，或者有更好的办法请务必分享给我，不胜感激。