Calling servlets methods

Question

Hi,
I have a servlet which calculates values i.e. calcServlet. I have another servlet which contains a method which uses JFreechart to plot values in a line chart i.e. plotServlet.
I want to pass the values in calcServlet to the method in plotServlet which will then be displayed in a web page.
Now I thought I could do something like the following in calcServlet:
plotServlet ps = new plotServlet();
ps.plotChart(values[]);This doesn't seem to be working and I keep getting an error saying getWriter has been called twice...From what I've read it isn't the correct way to call the method anyhow. It can be called from a html form (This isn't suitable for me)...
I would really appreciate if someone would give me a simple example on how to call another servlet method.
Many thanks in advance.

Answer 1

Don't do it!
As the other poster said, create a graphing class. I'll call it MyGraphClass. This class is not a servlet! It is a pure graphing generator.
You can give it a method like this: public void output(OutputStream out) { }. The calc servlet would then have code like this:
myGraphClass = new MyGraphClass(...);
myGraphClass.process(data);
OutputStream out = response.getOutputStream();
myGraphClass.output(out);Do you see how this works?
The cool thing here is you can use this MyGraphClass in many contexts. Maybe you want to use it for something totally different, like a GUI application that displays data, etc. It has no dependencies on servlets. All it does is generate its output.
Oh and don't forget, you need to set the output content type or the image will not display!