Issue with String Buffer in java

Question

I have a servlet in which the from InputStream I am getting the my form data in XML format. I am able to get retrieve the form data in XML format and able to write the same in file. If I open the file I am able to see my form data.

Now the issue is, When i try to append the form data to the string buffer it is not happening. I tried buffer.append(). After that method When I try to print the string buffer value nothing is showing/printing in the console.

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
                // TODO Auto-generated method stub
                 response.setContentType("html/text");
             PrintWriter out = response.getWriter();
             out.println("doPost Method is excecuting");
             DataInputStream in = new DataInputStream (request.getInputStream());
             StringBuffer buffer = new StringBuffer();
             File file = new File("reqOutput.txt");
             file.createNewFile();
             FileWriter writer = new FileWriter(file); 
             int value;
             while ((value=in.read()) != -1) {
                             buffer.append(value);
                        writer.write(value);
                      }
             System.out.println("Value is : "+ buffer.toString()); // Nothing is printing
             writer.flush();
             writer.close();
}

What's wrong with my code.Any suggestions please.

Answer 1

Here is your code modified to read from a file:

    public static void main(final String[] args) throws Exception {
        BufferedReader in = null;
        try {
            in = new BufferedReader(new FileReader("test"));
            final StringBuilder sb = new StringBuilder();
            String line;
            while ((line = in.readLine()) != null) {
                sb.append(line);
            }
            System.out.println("Value is : " + sb.toString());
        } finally {
            if (in != null) {
                in.close();
            }
        }
    }

I added a BufferedReader around the FileReader to optimize the reading. I switched from reading one character at a time to reading line by line. This also gives you the results as String so you don't have to convert the int.

Furthermore I added resource handling (pre-7 style and without exception handling) and switched to StringBuilder.

Output:

hello world! -> Value is : hello world!

I think there is another problem, not in this part of your code.

Additional comments on your code (not related to the question):

StringBuffer is a thread-safe implementation. If you have no need for this (like in your servlet example) you'd better use StringBuilder.

Don't close resources within the code block, use a try-finally (or since Java 7 try-with-resources) to guarantee resources are always closed, even when exceptions occur in the block somewhere.