为什么上传大文件就是空值，而上传小文件没有问题

项目有有时候会有大文件上传，四五百M，有时候上传接收不到流
可是上传小文件就没有问题
就是用得Formfile
好奇怪
项目架子struts1+spring2.5+hibernate

上传文件时，会处理request中的内容。
最终才会调用commonupload组件上传
struts中类
org.apache.struts.upload.CommonsMultipartRequestHandler
做了这一操作
[code="java"] public void handleRequest(HttpServletRequest request)
throws ServletException {
// Get the app config for the current request.
ModuleConfig ac =
(ModuleConfig) request.getAttribute(Globals.MODULE_KEY);

    // Create and configure a DIskFileUpload instance.
    DiskFileUpload upload = new DiskFileUpload();

    // The following line is to support an "EncodingFilter"
    // see http://issues.apache.org/bugzilla/show_bug.cgi?id=23255
    upload.setHeaderEncoding(request.getCharacterEncoding());

    // Set the maximum size before a FileUploadException will be thrown.
    upload.setSizeMax(getSizeMax(ac));

    // Set the maximum size that will be stored in memory.
    upload.setSizeThreshold((int) getSizeThreshold(ac));

    // Set the the location for saving data on disk.
    upload.setRepositoryPath(getRepositoryPath(ac));

    // Create the hash tables to be populated.
    elementsText = new Hashtable();
    elementsFile = new Hashtable();
    elementsAll = new Hashtable();

    // Parse the request into file items.
    List items = null;

    try {
        items = upload.parseRequest(request);
    } catch (DiskFileUpload.SizeLimitExceededException e) {
        // Special handling for uploads that are too big.
        request.setAttribute(MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED,
            Boolean.TRUE);

        return;
    } catch (FileUploadException e) {
        log.error("Failed to parse multipart request", e);
        throw new ServletException(e);
    }

    // Partition the items into form fields and files.
    Iterator iter = items.iterator();

    while (iter.hasNext()) {
        FileItem item = (FileItem) iter.next();

        if (item.isFormField()) {
            addTextParameter(request, item);
        } else {
            addFileParameter(item);
        }
    }
}[/code]

而在代码
[code="java"]upload.setSizeMax(getSizeMax(ac))[/code]
中会设置上传的最大值限制，如果超过最大值，会在request当值一个标识过大的参数值为true
[code="java"]request.setAttribute(MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED,
Boolean.TRUE);[/code]

然后调用者会根据request的MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED是不是true来决定来不要放null值

当然这个最大值也是可以配置文件中配置的。注意最后在配置的数字后带上M,K子符号
[code="java"] [/code]

Struts的默认的最大上传文件有限制。

enctype="multipart/form-data"去掉

可以在 struts.xml中配置大小（以kb计）

[code="xml"]
[/code]

但是，大文件还是建议用FTP。

http://blog.csdn.net/foamflower/archive/2008/08/29/2850067.aspx

试试看这个解决方法。

参考解决方案
http://blog.csdn.net/iwindyforest/archive/2008/01/25/2065791.aspx