X11 server problem

Question

Product:           Java Web Application
Operating system:     RedHat Linux 7.1
Web Server:     Tomcat
Application server:     Tomcat 3.2.4
Database server:     MySQL 3.23.49
Java Architecture:     JSP (presentation) + Java Bean (Business logic)
We are doing image annotation in some of our Java beans using Java AWT package with the following code. When we are running this code on a RedHat Linux 7.1 web server, we get "X11 server error" which says that the display variable can't have a value of :0. When we try to set the value for using xhost command it says that it is unable to set the value. I have logged is as the root. The same command runs successfully in local RedHat Linux 7.1 machine and the application is running without any problem. What could be wrong? Can any other parameter affect this? If, so how to set them? Or do we need to istall any other packages or patches?
f_obj_frame = new Frame();
f_obj_frame.addNotify();
          MediaTracker mt=new MediaTracker(f_obj_frame);
          image=Toolkit.getDefaultToolkit().getImage(f_str_source_path);
          mt.addImage(image,0);
          mt.waitForAll();
          f_int_width = image.getWidth(f_obj_frame);
          f_int_height = image.getHeight(f_obj_frame);
          offscreen = f_obj_frame.createImage(f_int_width,f_int_height);
          f_obj_graphics = offscreen.getGraphics();
          f_obj_graphics.drawImage(image,0,0,f_obj_frame);
f_obj_graphics.setColor(f_obj_font_color);
f_obj_graphics.setFont(f_obj_font_style);
          setXYPosition();
f_obj_graphics.drawString(f_str_annotate_text,f_int_Xpos,f_int_Ypos);
encodeGif();
          mt.removeImage(image);
     f_obj_frame.removeNotify();
          mt=null;

Answer 1

You seem to have a problem with your DISPLAY environment variable.
Do echo $DISPLAY to see what the DISPLAY is set to.