you can create a new instance of filereader
like
FileReader fr = new FileReader(..............) //complete syntax
see book/
and then use the command if
File f1 = new File("ex.test");
if f1.exists();

If your doing this for a local html page, you can use JavaScript and ActiveX:

function getFile(filespec) {
var fso, f;
fso = new ActiveXObject("Scripting.FileSystemObject");
f = fso.GetFile(filespec);
return f;
}

Where filespec is an absolute or relative path to the specified file.
(Unless you set the current directory, the path will be relative to the
user's desktop)