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.
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?
formPanel.setAction(GWT.getModuleBaseURL()+"uploadHandler");
formPanel.setMethod(Method.POST);
when we use formPanel.submit(),we can invoke the servlet and get the file upload details.
Related
I want to enhance this question. How can I create File Destination Chooser (as like JFileChooser) in GWT?
I had googled for a long time to get it in GWT. I found GWT FileUpload in most.
Any Suggestions for it ?
UPDATE: After clearing on question
Well, for this you would need a Download Servlet for the file. There in HttpServletResponse you will fill the content with the file and header with file types and all.
And from your client side call the URL.
For prompting case, it depends upon the browser configuration. You cannot force browser to open location prompt.
For achieving download only, you can refer to download file using gwt
i'm beginner with GXT and i'm wondering if there is a way to parse a file and extract some informations without uploading it.
i created a formpanel that contains an uploadFile form but i don't know waht's next, how to get the complete path of the file so i can read/write with java io or how to retrieve the file or is there an alternatif solution, thank you.
Best Regards.
You can do it in some modern browsers using bleeding edge HTML5 apis for which you would need to use GWT JSNI code. There are no api's from GWT team as is.
HTML5 FileReader
FileReader includes four options for reading a file, asynchronously:
FileReader.readAsBinaryString(Blob|File) - The result property will contain the file/blob's data as a binary string.
FileReader.readAsText(Blob|File, opt_encoding) - The result property will contain the file/blob's data as a text string.
FileReader.readAsDataURL(Blob|File) - The result property will contain the file/blob's data encoded as a data URL.
FileReader.readAsArrayBuffer(Blob|File) - The result property will contain the file/blob's data as an ArrayBuffer object.
Example of GWT wrapper over these -
https://github.com/bradrydzewski/gwt-filesystem
You can read about it more from here - How to retrieve file from GWT FileUpload component?
IMHO you cannot read it .
Due to security reasons javascript(gwt) doesn't have access to the system drives files.
http://en.wikipedia.org/wiki/JavaScript#Security
see Opening a file in local file system in javascript
In order to get the file you need to make a server call.
Instead you can do your validation server side and throw proper messages to user.
P.S : i am not considering modern browser concept.What happens if someone opened in other than so called modern browsers?? Will the programm runs same?? Its always better to do server side validation..
our Boss wants us to build a client only GWT App. so no server side coding will be involved in our GWT app.
Now we use a FileUpload widget to select a file from user file-system. most Browsers -for security reasons- don't allow FileUpload to return the full path of selected file. a real problem for us!
Is there a way, client-side, to fetch the filepath from a FileUpload widget?
any clever workaround or any other GWT widget that enables user file selection and returns selected file full path in file-system?
thanks.
You cannot get the full path of a selected file of an input element. The path will be absent or changed to avoid security risks in almost every browser browser.
You can get the file's name, and even its content, with the HTML5 FileAPI.
I have a .NET web service that takes a byte array.
I have a GWT client where I want the user to select a file using the FileUpload control and send it to the web service via HTTP stream.
The file upload control contains a method to get the file path of the selected file. How can I then get that file and convert it to a byte array?
I'm open to suggestions on how to get the file to my web service, not quite sure the Byte array will work...
If you want to convert the file in GWT, meaning in the browser. It's not possible to do in the browser using only JavaScript. FileUpload is a html input type file upload can only send the file to a server as in submit a form. For security reasons browsers can't read files from your file system. (You could use a plugin like a flash plugin to get it to work, although I have no examples at hand).
If you want to send the file content to your webservice, you need to or upload it directly to the webservice or send it to another server, convert it and from that server submit it to your webservice or write or find some (flash) plugin that does it for you.
This link maybe helpful yo you How to convert a byte array to a string, and string to a byte array with GWT
The String(byte[] bytes) constructor and String.getBytes() method are not implemented by GWT JRE emulation String class.
This is not possible purely in Javascript(yet) but could be done with flash or a signed applet. Personally what I would do is create a signed applet that would be somewhere on the page but not visible. When the user selects a file to send to the server you would get the file location from the input and send it to the applet which will load the file and return the data to Javascript as a byte array. If you are flexable with changing the web service to accept multi-part form data then you can do so and just include the file upload field as part of a form and submit the form. Now what you want to do is possible with HTML5 and a demonstration can be seen here, so if you are capable of specifying that the users be using at least a semi-HTML5 compliant browser such as FF3.6 or Chrome 6 you may be in luck.
If there's a way for the client side GWT code to pre-process a file on the client computer?
For example, to calculate a checksum of it before submitting the file to the server.
No it is not possible. The manipulation of the file is done by the browser, not the HTML code.
Think about it, GWT is 100% javascript. And javascript has no access whatsoever of the file in your computer. That would be an pretty big security risk! GWT "wraps" the file input box so it can be displayed inside the GWT panel. But once you press the "upload" button, the upload is done by the browser.
You could do file manipulation with another technology however. Java applets for example. But that is outside of GWT area...
Using GWT, there is no way to read files on the client side yet. However, in HTML5, you can read files without uploading to a server using the "File API".
Links are provided below.
File API tutorial on html5rocks.com
Example of how to use File API in GWT via JSNI
I'm pretty sure that because GWT code compiles to pure JavaScript, there isn't a way without requiring some third-party browser plugin.
Do you mean from an <input type="file"...> file upload field in a form?
The short answer is no-- file uploads are handled by the browser, and are sent directly to the server (as an ENCODING_MULTIPART POST). And security restrictions on JavaScript mean there's no way to workaround that restriction.