怎样获取form-data方式POST的数据

转自：http://ju.outofmemory.cn/entry/201812

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：

------WebKitFormBoundaryd7FGw9vQyyFIAYd7Content-Disposition: form-data; name="uuid"56------WebKitFormBoundaryd7FGw9vQyyFIAYd7Content-Disposition: form-data; name="tagIds"------WebKitFormBoundaryd7FGw9vQyyFIAYd7Content-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                    }                }            }        }    }}

POST 获取 Data 数据 form