Determine the size of a file upload before reading it all in in the Apache FileUpload Streaming API

apache-commons-fileupload, file-upload, java

Solution

There's no way to know the size of a part of a multipart request without consuming the whole HTTP request body. And once the consuming of the HTTP request body has started, you cannot stop consuming it halfway. It has to be consumed until the last byte before a response can ever be returned. That's just the nature of HTTP and TCP/IP. To keep the server memory usage low, you can however just discard the read bytes when they exceeds the size (i.e. check it inside the read loop and don't assign them to any variable).

Your best bet is to validate the file length in JavaScript before the upload takes place. This is supported in browsers supporting HTML5 `File` API. The current versions of Firefox, Chrome, Safari, Opera and Android support it. IE9 doesn't support it yet, it'll be in the future IE10.

<input type="file" ... onchange="checkFileSize(this)" />

Where the `checkFileSize()` look something like this

function checkFileSize(inputFile) {
    var max = 10 * 1024 * 1024; // 10MB

    if (inputFile.files && inputFile.files[0].size > max) {
        alert("File too large."); // Do your thing to handle the error.
        inputFile.value = null; // Clear the field.
    }
}

Problem

There are two ways to use the Apache FileUpload Library. FileUpload http://commons.apache.org/fileupload/using.html And Streaming FileUpload API http://commons.apache.org/fileupload/streaming.html They both work great except that the streaming API does not seem to have a way to check the fileSize before processing the stream. Is this because the Streaming API fundamentally does not know the file size or because I need to manually read some headers or something to get the Multipart upload size?

Original source