昨天君仔问我说遇到一个诡异的问题，他有一个controller方法，用x-www-form-urlencoded方式提交表单就可以正常绑定数据，但是用form-data方式提交就绑定不了：
@Controller
@RequestMapping("/tag")
public class TagController {
@Autowired
private NanTianMenFacade nanTianMenFacade;
@RequestMapping(value = "/uploadTags")
@ResponseBody
public TagUploadResult uploadTags(TagParams params) {
String tagIds = params.getTagIds();
String uuid = params.getUuid();
TagUploadResult result = null;
try {
result = nanTianMenFacade.uploadTags(tagIds, uuid);
} catch (Exception e) {
result = new TagUploadResult();
result.setS(0);
}
return result;
}
}
对于我来说，一直都是用x-www-form-urlencoded提交表单数据，除非是要上传文件，才会使用form-data方式。也一直以为Spring对不同的提交方式应该是透明的。不过确实用form-data提交普通表单，确实是拿不到提交的数据。DEBUG发现，request.getParameterMap()返回的就是空的！
然后发现org.apache.commons.io.IOUtils.toString(request.getInputStream());其实是有返回提交的数据的：
------WebKitFormBoundaryd7FGw9vQyyFIAYd7
Content-Disposition: form-data; name="uuid"
123456
------WebKitFormBoundaryd7FGw9vQyyFIAYd7
Content-Disposition: form-data; name="tagIds"
36
------WebKitFormBoundaryd7FGw9vQyyFIAYd7
Content-Disposition: form-data; name="aaa"
bbb
------WebKitFormBoundaryd7FGw9vQyyFIAYd7--
也就是数据其实是有正常提交到后台的。那么就是这种方式提交的数据，并没有放在pararmeterMap中了。而是要自己去解析这个inputstream的内容，再放回parameterMap中，这样Spring才能够绑定？这个不就是multipartResolver做的事情吗？试着配置了一下，发现果然可以了：
<bean id="multipartResolver"
class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<property name="maxUploadSize" value="10000000"></property>
</bean>
然后深入Spring MVC的代码，其实是做了一个判断，如果是Multipart，那么就会进行解析，然后将解析结果放回parameterMap中：
package org.springframework.web.servlet;
public class DispatcherServlet extends FrameworkServlet {
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = processedRequest != request;
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest, false);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
try {
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
applyDefaultViewName(request, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Error err) {
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
/**
* Convert the request into a multipart request, and make multipart resolver available.
* <p>If no multipart resolver is set, simply use the existing request.
* @param request current HTTP request
* @return the processed request (multipart wrapper if necessary)
* @see MultipartResolver#resolveMultipart
*/
protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
if (request instanceof MultipartHttpServletRequest) {
logger.debug("Request is already a MultipartHttpServletRequest - if not in a forward, " +
"this typically results from an additional MultipartFilter in web.xml");
}
else {
return this.multipartResolver.resolveMultipart(request);
}
}
// If not returned before: return original request.
return request;
}
}
package org.springframework.web.multipart.commons;
public class CommonsMultipartResolver extends CommonsFileUploadSupport
implements MultipartResolver, ServletContextAware {
public MultipartHttpServletRequest resolveMultipart(final HttpServletRequest request) throws MultipartException {
Assert.notNull(request, "Request must not be null");
if (this.resolveLazily) {
return new DefaultMultipartHttpServletRequest(request) {
@Override
protected void initializeMultipart() {
MultipartParsingResult parsingResult = parseRequest(request);
setMultipartFiles(parsingResult.getMultipartFiles());
setMultipartParameters(parsingResult.getMultipartParameters());
setMultipartParameterContentTypes(parsingResult.getMultipartParameterContentTypes());
}
};
}
else {
MultipartParsingResult parsingResult = parseRequest(request);
return new DefaultMultipartHttpServletRequest(request, parsingResult.getMultipartFiles(),
parsingResult.getMultipartParameters(), parsingResult.getMultipartParameterContentTypes());
}
}
/**
* Parse the given servlet request, resolving its multipart elements.
* @param request the request to parse
* @return the parsing result
* @throws MultipartException if multipart resolution failed.
*/
@SuppressWarnings("unchecked")
protected MultipartParsingResult parseRequest(HttpServletRequest request) throws MultipartException {
String encoding = determineEncoding(request);
FileUpload fileUpload = prepareFileUpload(encoding);
try {
List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
return parseFileItems(fileItems, encoding);
}
catch (FileUploadBase.SizeLimitExceededException ex) {
throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
}
catch (FileUploadException ex) {
throw new MultipartException("Could not parse multipart servlet request", ex);
}
}
}
package org.apache.commons.fileupload;
public abstract class FileUploadBase {
/**
* Processes an <a href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a>
* compliant <code>multipart/form-data</code> stream.
*
* @param request The servlet request to be parsed.
*
* @return A list of <code>FileItem</code> instances parsed from the
* request, in the order that they were transmitted.
*
* @throws FileUploadException if there are problems reading/parsing
* the request or storing files.
*/
@Override
public List<FileItem> parseRequest(HttpServletRequest request)
throws FileUploadException {
return parseRequest(new ServletRequestContext(request));
}
/**
* Processes an <a href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a>
* compliant <code>multipart/form-data</code> stream.
*
* @param ctx The context for the request to be parsed.
*
* @return A list of <code>FileItem</code> instances parsed from the
* request, in the order that they were transmitted.
*
* @throws FileUploadException if there are problems reading/parsing
* the request or storing files.
*/
public List<FileItem> parseRequest(RequestContext ctx)
throws FileUploadException {
List<FileItem> items = new ArrayList<FileItem>();
boolean successful = false;
try {
FileItemIterator iter = getItemIterator(ctx);
FileItemFactory fac = getFileItemFactory();
if (fac == null) {
throw new NullPointerException("No FileItemFactory has been set.");
}
while (iter.hasNext()) {
final FileItemStream item = iter.next();
// Don't use getName() here to prevent an InvalidFileNameException.
final String fileName = ((FileItemIteratorImpl.FileItemStreamImpl) item).name;
FileItem fileItem = fac.createItem(item.getFieldName(), item.getContentType(),
item.isFormField(), fileName);
items.add(fileItem);
try {
Streams.copy(item.openStream(), fileItem.getOutputStream(), true);
} catch (FileUploadIOException e) {
throw (FileUploadException) e.getCause();
} catch (IOException e) {
throw new IOFileUploadException(format("Processing of %s request failed. %s",
MULTIPART_FORM_DATA, e.getMessage()), e);
}
final FileItemHeaders fih = item.getHeaders();
fileItem.setHeaders(fih);
}
successful = true;
return items;
} catch (FileUploadIOException e) {
throw (FileUploadException) e.getCause();
} catch (IOException e) {
throw new FileUploadException(e.getMessage(), e);
} finally {
if (!successful) {
for (FileItem fileItem : items) {
try {
fileItem.delete();
} catch (Throwable e) {
// ignore it
}
}
}
}
}
}
