Memory Allocation Problems

Question

My application seems to not free resources the way I would like it to. The main interface consumes somewhere around 40MB. The application has an option to export data to a few PDFs (via itext and JFreeChart). This is handled through a popup JFrame where the user can select options for export. During the export, memory usage spikes to near 105MB, which though concerning, isn't the main problem. Once the export JFrame has been disposed and control is returned the main window, memory usage stays at ~ 105MB and if you export again, the memory usage doesn't budge, leading me to believe that the Objects used during the export aren't being released. I know that memory management is temperamental in Java, but I can't figure out what's going on here.
Here is an overview of what's happening:
MainViewer -> SaveView -> ExportFileController:
I am currently exporting two PDFs: One containing graphs created by JFreeChart and another containing a table created by itext. I've tested them independently and both seem to stay in memory even after I've called document.close() and SaveView.dispose().
Here is how I'm writing my charts:
public void writeCharts()
          Iterator chartIter = allCharts.iterator();
          try
               System.out.println("Writing Charts: Total Number: " + allCharts.size());
               String outputFile = outputDir.getPath()+"/curvefits.pdf";               
               writer = PdfWriter.getInstance(document, new FileOutputStream(outputFile));
               document.open();
               while(chartIter.hasNext())               
                    numpages++;
                    JFreeChart currentChart = (JFreeChart)chartIter.next();
                    PdfContentByte cb = writer.getDirectContent();
                    PdfTemplate tp = cb.createTemplate(width, height);
                    Graphics2D g2d = tp.createGraphics(width, height, new DefaultFontMapper());
                    Rectangle2D r2d = new Rectangle2D.Double(0, 0, width, height);
                    System.out.println("Writting Chart: " + currentChart.getTitle().getText());          
                    currentChart.draw(g2d, r2d);
                    g2d.dispose();
                    cb.addTemplate(tp, 0, 0);
                    document.newPage();
                    writer.releaseTemplate(tp);  //I had heap errors before I added this
          catch(Exception e)
               e.printStackTrace();
          document.close();
          writer.flush();
          writer.close();
          allCharts.clear();
          allCharts.trimToSize();          
          System.gc();    //I'm explicitly trying to free up the resources here
          System.runFinalization();
}

Answer 1

warnerja wrote:
Hard to say.
Once it loads classes, it won't give that memory back, but any memory used on the heap which is no longer needed may be reclaimed.
Does it keep climbing on repeated exports, or does it basically peak on one export and remain at that usage level upon repeated exports?It peaks on one export and then remains the same on repeated exports (roughly ~105MB). What scares me is the my test set is relatively small (perhaps as small as 1%) of what this application could be used for. I can do some things to minimize memory usage (like writing one page at a time and then appending so I don't have to keep the whole output stream open) at the expense of speed, but some where there has to be a data structure containing all of the items to be written. If the JVM NEVER gives the memory back then this will pretty much cripple the user's system.