java - checking file content before uploading to server

i have got a situation now.

I need to develop a webpage where user can select a file to upload and before uploading the file to server i need to check first few lines of the file whether the data is valid or not and if the d开发者_高级运维ata is valid then upload the file, if not through an error message.

the file will be text file.

thanks,

Sandeep

HTML/Javascript does not offer a way of reading the contents of a local file. You must either upload it and check it in the server.

If you really want a client side check, you then must build a signed applet(or even ActiveX) to run in your webpage and handle the upload instead of using plain HTML.

You should perform your validation on the server side, right before you perform the upload.