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Message:

Correct usage of Java.IO classes with servlets

Posted by Chris Adams on May 07, 2001 at 6:07 PM

I am trying to create a servlet that serves as a broker within a 'web services' model.
For example - there exists a web service that upon receiveing the correct HTTP GET request, in XML format, it will return to me a JPG formatted image of my choice. My servlet actually receives a request first, as its the real client app, but if I don't have that image I go and get it from this external web service.

An example GET request that I'll generate to send out to the service might be:

String XMLRequest= ""

I send this string using a simple URLConnection Object, for example:

URL url = new URL("http://10.3.1.56/imageserver.asp");
URLConnection connection = url.openConnection();
connection.setDoOutput(true);
PrintWriter out1 = new PrintWriter(connection.getOutputStream());
out1.println(XML_Request);
out1.close();

Now I want to get my response off that connection:

BufferedInputStream in = new BufferedInputStream(connection.getInputStream());

The problem is that I do not always know what I will get back. If the image is unavailable or my request string is bad, I'll get an XML error message back...like:

BufferedOutputStream out = new BufferedOutputStream(response.getOutputStream());

Finally, I guess (low confidence here), I want to transfer the data from the 'in' buffer array to the 'out' buffer array and then do a out.flush(). Is that smart? I also thought to use the read(byte array) method like:

while(in.read(out));

but I get an error stating 'in' is not a buffer array. What?

Question 1.) First theory. What combination of OutputStream classes should I use here so that if I get the image data back, I can forward it on to the response losing the least amount of time and processing/memory?

Question 2.) Java documentation for BufferedInputStream states that it creates a buffered array..."When the BufferedInputStream is created, an internal buffer array is created." WHere is it?

Question 3.) How should I work with transfering binary data from one buffer array to another? (Perhaps an example from question 1 makes this clear.) Does the flush write it out like I think it does?

Question 4.) How should I deal with the fact, I may get two types of data back(binary or XML text) and its unknown when?

I sincerely thank you for a response and will be happy to share results afterward.

Regards,
Chris Adams

• java dihan July 18, 2001 at 12:36 AM (0)