MultipartConfigElement
MultipartConfigElement 是 javax.servlet 包中的是 JavaEE Servlet 规范定义的标准包。
该类定义了Http服务上传文件存储位置、最大文件大小、最大请求的长度
javax.servlet.MultipartConfigElement
public class MultipartConfigElement {
private final String location;// = "";
private final long maxFileSize;// = -1;
private final long maxRequestSize;// = -1;
private final int fileSizeThreshold;// = 0;
。。。。
}以Springboot Tomcat为例，Tomcat 的 Request 请求会被传递到 SpringMVC 的 DispatcherServlet 中，在 doDispartch() 方法会 Request 的 getParts() 方法被调用， 会去获取 MultipartConfigElement 对象，从中获取存储位置将上传的文件存储在临时存储位置，这些文件以List<Part>的形式存在于 StandardMuiltpartHttpSevrletRequest 中返回给 DispatcherServlet 继续处理。在整个请求处理完成后，DispatcherServlet 会调用 StandardServletMultipartResolver 的 cleanupMultipart() 的方法，清理掉所有的缓存文件。
org.springframework.web.servlet.DispatcherServlet
/**
* Process the actual dispatching to the handler.
* <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
* The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
* to find the first that supports the handler class.
* <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
* themselves to decide which methods are acceptable.
* @param request current HTTP request
* @param response current HTTP response
* @throws Exception in case of any kind of processing failure
*/
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); // 将请求转化为 multipart request 让多媒体处理器可生效
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == 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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest); // 请求处理完成后清除多媒体文件
}
}
}
}
/** 将请求转化为 multipart request 让多媒体处理器可生效
* 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 (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
if (request.getDispatcherType().equals(DispatcherType.REQUEST)) {
logger.trace("Request already resolved to MultipartHttpServletRequest, e.g. by MultipartFilter");
}
}
else if (hasMultipartException(request)) {
logger.debug("Multipart resolution previously failed for current request - " +
"skipping re-resolution for undisturbed error rendering");
}
else {
try {
return this.multipartResolver.resolveMultipart(request);
}
catch (MultipartException ex) {
if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
logger.debug("Multipart resolution failed for error dispatch", ex);
// Keep processing error dispatch with regular request handle below
}
else {
throw ex;
}
}
}
}
// If not returned before: return original request.
return request;
}org.springframework.web.multipart.support.StandardServletMultipartResolver
@Override
public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
}org.springframework.web.multipart.support.StandardMultipartHttpServletRequest
/**
* Create a new StandardMultipartHttpServletRequest wrapper for the given request.
* @param request the servlet request to wrap
* @param lazyParsing whether multipart parsing should be triggered lazily on
* first access of multipart files or parameters
* @throws MultipartException if an immediate parsing attempt failed
* @since 3.2.9
*/
public StandardMultipartHttpServletRequest(HttpServletRequest request, boolean lazyParsing)
throws MultipartException {
super(request);
if (!lazyParsing) {
parseRequest(request);
}
}
private void parseRequest(HttpServletRequest request) {
try {
Collection<Part> parts = request.getParts();
this.multipartParameterNames = new LinkedHashSet<>(parts.size());
MultiValueMap<String, MultipartFile> files = new LinkedMultiValueMap<>(parts.size());
for (Part part : parts) {
String headerValue = part.getHeader(HttpHeaders.CONTENT_DISPOSITION);
ContentDisposition disposition = ContentDisposition.parse(headerValue);
String filename = disposition.getFilename();
if (filename != null) {
if (filename.startsWith("=?") && filename.endsWith("?=")) {
filename = MimeDelegate.decode(filename);
}
files.add(part.getName(), new StandardMultipartFile(part, filename));
}
else {
this.multipartParameterNames.add(part.getName());
}
}
setMultipartFiles(files);
}
catch (Throwable ex) {
handleParseFailure(ex);
}
}
protected void handleParseFailure(Throwable ex) {
String msg = ex.getMessage();
if (msg != null && msg.contains("size") && msg.contains("exceed")) {
throw new MaxUploadSizeExceededException(-1, ex);
}
throw new MultipartException("Failed to parse multipart servlet request", ex);
}org.apache.catalina.connector.Request
/**
* {@inheritDoc}
*/
@Override
public Collection<Part> getParts() throws IOException, IllegalStateException,
ServletException {
parseParts(true);
if (partsParseException != null) {
if (partsParseException instanceof IOException) {
throw (IOException) partsParseException;
} else if (partsParseException instanceof IllegalStateException) {
throw (IllegalStateException) partsParseException;
} else if (partsParseException instanceof ServletException) {
throw (ServletException) partsParseException;
}
}
return parts;
}
private void parseParts(boolean explicit) {
// Return immediately if the parts have already been parsed
if (parts != null || partsParseException != null) {
return;
}
Context context = getContext();
MultipartConfigElement mce = getWrapper().getMultipartConfigElement();
if (mce == null) {
if(context.getAllowCasualMultipartParsing()) {
mce = new MultipartConfigElement(null, connector.getMaxPostSize(),
connector.getMaxPostSize(), connector.getMaxPostSize());
} else {
if (explicit) {
partsParseException = new IllegalStateException(
sm.getString("coyoteRequest.noMultipartConfig"));
return;
} else {
parts = Collections.emptyList();
return;
}
}
}
Parameters parameters = coyoteRequest.getParameters();
parameters.setLimit(getConnector().getMaxParameterCount());
boolean success = false;
try {
File location;
String locationStr = mce.getLocation();
if (locationStr == null || locationStr.length() == 0) {
location = ((File) context.getServletContext().getAttribute(
ServletContext.TEMPDIR));
} else {
// If relative, it is relative to TEMPDIR
location = new File(locationStr);
if (!location.isAbsolute()) {
location = new File(
(File) context.getServletContext().getAttribute(ServletContext.TEMPDIR),
locationStr).getAbsoluteFile();
}
}
if (!location.exists() && context.getCreateUploadTargets()) {
log.warn(sm.getString("coyoteRequest.uploadCreate",
location.getAbsolutePath(), getMappingData().wrapper.getName()));
if (!location.mkdirs()) {
log.warn(sm.getString("coyoteRequest.uploadCreateFail",
location.getAbsolutePath()));
}
}
if (!location.isDirectory()) {
parameters.setParseFailedReason(FailReason.MULTIPART_CONFIG_INVALID);
partsParseException = new IOException(
sm.getString("coyoteRequest.uploadLocationInvalid",
location));
return;
}
// Create a new file upload handler
DiskFileItemFactory factory = new DiskFileItemFactory();
try {
factory.setRepository(location.getCanonicalFile());
} catch (IOException ioe) {
parameters.setParseFailedReason(FailReason.IO_ERROR);
partsParseException = ioe;
return;
}
factory.setSizeThreshold(mce.getFileSizeThreshold());
ServletFileUpload upload = new ServletFileUpload();
upload.setFileItemFactory(factory);
upload.setFileSizeMax(mce.getMaxFileSize());
upload.setSizeMax(mce.getMaxRequestSize());
parts = new ArrayList<>();
try {
List<FileItem> items =
upload.parseRequest(new ServletRequestContext(this));
int maxPostSize = getConnector().getMaxPostSize();
int postSize = 0;
Charset charset = getCharset();
for (FileItem item : items) {
ApplicationPart part = new ApplicationPart(item, location);
parts.add(part);
if (part.getSubmittedFileName() == null) {
String name = part.getName();
String value = null;
try {
value = part.getString(charset.name());
} catch (UnsupportedEncodingException uee) {
// Not possible
}
if (maxPostSize >= 0) {
// Have to calculate equivalent size. Not completely
// accurate but close enough.
postSize += name.getBytes(charset).length;
if (value != null) {
// Equals sign
postSize++;
// Value length
postSize += part.getSize();
}
// Value separator
postSize++;
if (postSize > maxPostSize) {
parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);
throw new IllegalStateException(sm.getString(
"coyoteRequest.maxPostSizeExceeded"));
}
}
parameters.addParameter(name, value);
}
}
success = true;
} catch (InvalidContentTypeException e) {
parameters.setParseFailedReason(FailReason.INVALID_CONTENT_TYPE);
partsParseException = new ServletException(e);
} catch (SizeException e) {
parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);
checkSwallowInput();
partsParseException = new IllegalStateException(e);
} catch (FileUploadException e) {
parameters.setParseFailedReason(FailReason.IO_ERROR);
partsParseException = new IOException(e);
} catch (IllegalStateException e) {
// addParameters() will set parseFailedReason
checkSwallowInput();
partsParseException = e;
}
} finally {
// This might look odd but is correct. setParseFailedReason() only
// sets the failure reason if none is currently set. This code could
// be more efficient but it is written this way to be robust with
// respect to changes in the remainder of the method.
if (partsParseException != null || !success) {
parameters.setParseFailedReason(FailReason.UNKNOWN);
}
}
}org.apache.tomcat.util.http.fileupload.FileUploadBase
/**
* 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<>();
boolean successful = false;
try {
FileItemIterator iter = getItemIterator(ctx);
FileItemFactory fac = getFileItemFactory();
final byte[] buffer = new byte[Streams.DEFAULT_BUFFER_SIZE];
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 = ((FileItemStreamImpl) item).getName();
FileItem fileItem = fac.createItem(item.getFieldName(), item.getContentType(),
item.isFormField(), fileName);
items.add(fileItem);
try {
Streams.copy(item.openStream(), fileItem.getOutputStream(), true, buffer); // 文件最终上传到temp目录到地方
} catch (FileUploadIOException e) {
throw (FileUploadException) e.getCause();
} catch (IOException e) {
throw new IOFileUploadException(String.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 (Exception ignored) {
// ignored TODO perhaps add to tracker delete failure list somehow?
}
}
}
}
}
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