Spring在发现包括multipart的请求后，会使用MultipartResolver的实现bean处理文件上传操作，现有採用Servlet3的

org.springframework.web.multipart.support.StandardServletMultipartResolver

和採用commons-fileupload的

org.springframework.web.multipart.commons.CommonsMultipartResolver

处理文件的上传须要重写接口MultipartResolver的parseRequest方法。

其涉及到的成员变量类型：

public CommonsFileUploadSupport() {this.fileItemFactory = newFileItemFactory();

<span style="white-space:pre">	</span>this.fileUpload = newFileUpload(getFileItemFactory());

}

protected DiskFileItemFactory newFileItemFactory() {

	return new DiskFileItemFactory();

}

DiskFileItemFactory#createItem

public FileItem createItem(String fieldName, String contentType,

		boolean isFormField, String fileName) {

	DiskFileItem result = new DiskFileItem(fieldName, contentType,

			isFormField, fileName, sizeThreshold, repository);

	FileCleaningTracker tracker = getFileCleaningTracker();

	if (tracker != null) {

		tracker.track(result.getTempFile(), this);

	}

	return result;

}

DiskFileItem#getOutputStream

public OutputStream getOutputStream()

	throws IOException {

	if (dfos == null) {

		File outputFile = getTempFile();

		dfos = new DeferredFileOutputStream(sizeThreshold, outputFile);

	}

	return dfos;

}

其默认採用暂时文件保存上传内容，若超过指定的内存限制大小，则直接存储为暂时文件