HTML <input type=file/> Validation

trotter_inc

Hi,

Im using this tag so that a user can use the Browse button and select a file.

However, the user can also type the name of the file into the field.

Its a web app and I need to put validation into my servlet to check if the file exists. The file paths will be in the form of \\machine123\dir1\file1.txt for example.

Validation needs to be done on the server, any idea how to go about this?

Thanks for you help guys....

muckwarrior

I'm a bit confused. Is the user suppose to select a file on their local machine or on the server? A bit more info on how it works would be useful.

kdouglas

well if the user types in a non-existent file, then surely the browser will pick up on this and throw an error, or when submitted to the server there just wont be any data available?

phil

You sound like you're confused.

Servlets run on the remote web server away from the client. If a client selects a file to upload, the servlet cannot check if the file exists or not. It can only work with the data presented to it by the browser.

You need to explain a little better what it is you're doing / trying to do.

The Corinthian

phil wrote:

If a client selects a file to upload, the servlet cannot check if the file exists or not.

Of course server can check if the file exists or not, just as it can validate any other variable after the form has been submitted.

trotter_inc wrote:

Validation needs to be done on the server, any idea how to go about this?

If no valid file has been submitted then the upload (separate to the pathname - which is also sent) will essentially be null, if it is simply not a valid file then you’ll have to parse through the file to identify and thus validate it.

Civilian_Target

trotter_inc wrote:

Hi,

Im using this tag so that a user can use the Browse button and select a file.

However, the user can also type the name of the file into the field.

Its a web app and I need to put validation into my servlet to check if the file exists. The file paths will be in the form of \\machine123\dir1\file1.txt for example.

You can't do that. You can't do any validation until you receive the POST array from your client. There's no way you can actually find out what the path of the file on the client machine is from that data, only the file name

Validation needs to be done on the server, any idea how to go about this?

Thanks for you help guys....

Sounds like you're doing this in Enterprise Java in which case your best bet is to use the Commons File Upload library ( http://jakarta.apache.org/commons/fileupload ) to deal with all your file handling. The isMultipartContent(req) method will check that you're receiving a valid POST array from the client for you and the isFormField() method will return true for text content (such as mime headers and client info) and false for binary data (ie. the file you want) and you can use that to extract and deal with the file as you see fit. I strongly recommend you check it out.