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Anybody know how GWT file upload works? I know about FileUpload widget and how to use it. I want to know what is its inner mechanism. We can't get contents of file from FileUpload widget in client and how it is going to server? I googled it but i didn't get solution.
Thanks in advance.
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The file is only a part of the data sent in the request, hence the multipart/form-data Content-Type header. If you want to send the file as the only content then you can directly add it as the request body and you set the Content-Type header to the MIME type of the file you are sending.
Multipart upload allows you to upload a single object as a set of parts. Each part is a contiguous portion of the object's data. You can upload these object parts independently and in any order. If transmission of any part fails, you can retransmit that part without affecting other parts.
Uploading is the process of putting web pages, images and files onto a web server. Downloading is the process of getting web pages, images and files from a web server. To make a file visible to everyone on the internet, you will need to upload it.
GWT's file upload makes use HTML's input element. The html input element is native html dom element which allows to select files from your system.
After selection you need to submit it to your server. This is done by the GWT's FormPanel.
In particular, FileUpload is only useful when used within a FormPanel, because the browser will only upload files using form submission.
Note:
1) You can read about how to code with formpanel and fileupload as answered here @ Basic File upload in GWT
2) If you are concerned with processing the file on client side and not pushing the file to server then you have limited options as mentioned here @ How to retrieve file from GWT FileUpload component?
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