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i want to web app that takes in a pdf file and displays it but i got a http 500 error.i thought it was get extracting the byte array from the request and adding it to the response output stream. well where was i wrong?

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getOutputStream().write(request.getParameter("f").getBytes()); response.getOutputStream().flush(); response.getOutputStream().close(); }

here is the html page

<body> <form action="display" method="post" enctype="multipart/form-data"> PDF FILE : <input type="file" name="f"> <input type="submit" value="display"> </form> </body>

here is the error that i got

java.lang.NullPointerException display.doPost(display.java:43) javax.servlet.http.HttpServlet.service(HttpServlet.java:641) javax.servlet.http.HttpServlet.service(HttpServlet.java:722
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  • Use Apache commons-fileupload for it. Commented Sep 25, 2013 at 9:20

3 Answers 3

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You should get a valid part from your multipart request. You can use Apache Commons FileUpload, or with Servlets 3.0 Spec:

Part filePart = request.getPart("f"); // Retrieves <input type="file" name="f"> InputStream filecontent = filePart.getInputStream(); // ... read input stream
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You want to send an PDF file to the browser, you should write a response.setContentType("application/pdf") before outputStream writes the stream;

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yeah but i got a null pointer exception...do you think that would have happened because i dint set the content type?
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Make sure to call response.getOutputStream() only once:

OutputStream os = response.getOutputStream(); os.write(bytes); os.flush(); os.close();

The uploaded file is not contained as a request parameter. That is the reason for the NullPointerException in your code. You must get the pdf content via the request's input stream. Use a third pary library or Servlet 3 spec for that purpose.

If you like to set http headers (i.e. for the content type), you should set them before writing any bytes to the OutputStream via response.setHeader().

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