I want to collect 400 data items from a text area with the method
        String myData = req.getParameter("textarea");
This gives the error message 'Error: 414 No detailed message' which implies that the request URI is too long.  How do I overcome the problem?

Looks to me like you might be using the GET method, which has a 1k limit ... try switching to the POST method where the limit is removed.    Can I also suggest a different name for your textarea - "textarea" will work, no doubt, but it might be confusing to anyone who has to look at your code in the future  

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