Getting Binary HTTP Post parameter in an Java/Tomcat/HttpServlet

Question

I have a binary value being URL Encoded, and then POSTed to an HttpServlet. The following code shows how I first attempted to extract this data. Very simple except that the result is a String, not bytes.

This seemed to work at first, except that an extra byte appeared three bytes from the end. What I eventually figured out was that my data was being treated as Unicode and converted from one Unicode encoding to UTF-8.

So, other that getting the entire post body and parsing it myself, how can I extract my data without treating it as a string after the url encoding is decoded? Have I misunderstood the specs for posted data in general, or is this a Java/Tomcat specific issue?

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    // Receive/Parse the request
    String requestStr = request.getParameter("request");
    byte[] rawRequestMsg = requestStr.getBytes();

Here is a snippet of the Python test script I'm using for the request:

    urlRequest = urllib.urlencode( {'request': rawRequest} )

    connection = urllib.urlopen(self.url, data = urlRequest)
    result = connection.readlines()
    connection.close()

Answer 1

Erm, don't use java.

Answer 2

you can do this with a servlet wrapper (HttpServletRequestWrapper)... catch the request and snatch the request body before its decoded

but the best way is probably to send the data as a file upload (multipart/form-data content type)

Answer 3

I think this should work (it treats request as a single-byte encoding, so transformation to String is completely reversible):

String someSingleByteEncoding = "ISO-8859-1";
request.setCharacterEncoding(someSingleByteEncoding);
String requestStr = request.getParameter("request"); 
byte[] rawRequestMsg = requestStr.getBytes(someSingleByteEncoding);

Answer 4

There are two possible solutions:

• ASCII-encode your data before POSTing it. Base64 would be a sensible choice. Decode it in your servlet and you have your original binary again.

• Use form content type multipart/form-data ( http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4 ) to encode your binary data as a stream of bytes; then your servlet can do servletRequest.getReader() to read the data in, again as a binary stream.