Java tutorial
/* * Copyright (c) 2012 Data Harmonisation Panel * * All rights reserved. This program and the accompanying materials are made * available under the terms of the GNU Lesser General Public License as * published by the Free Software Foundation, either version 3 of the License, * or (at your option) any later version. * * You should have received a copy of the GNU Lesser General Public License * along with this distribution. If not, see <http://www.gnu.org/licenses/>. * * Contributors: * Data Harmonisation Panel <http://www.dhpanel.eu> */ package eu.esdihumboldt.hale.server.status.war.components.memory; import org.apache.wicket.ajax.AjaxRequestTarget; import org.apache.wicket.ajax.AjaxSelfUpdatingTimerBehavior; import org.apache.wicket.ajax.markup.html.AjaxFallbackLink; import org.apache.wicket.markup.head.CssHeaderItem; import org.apache.wicket.markup.head.IHeaderResponse; import org.apache.wicket.markup.head.JavaScriptHeaderItem; import org.apache.wicket.markup.html.WebMarkupContainer; import org.apache.wicket.markup.html.basic.Label; import org.apache.wicket.markup.html.panel.Panel; import org.apache.wicket.request.resource.CssResourceReference; import org.apache.wicket.request.resource.JavaScriptResourceReference; import org.apache.wicket.resource.JQueryPluginResourceReference; import org.apache.wicket.util.time.Duration; /** * The main page for the memory view. It contains labels that show the current * memory situtation and a self-updating chart showing the memory values of the * last 60 seconds. * * @author Michel Kraemer */ public class MemoryPanel extends Panel { private static final long serialVersionUID = 5228052421880544175L; /** * Default constructor * * @param id the component ID */ public MemoryPanel(String id) { super(id); // calculate start values long curMax = Runtime.getRuntime().maxMemory() / 1024 / 1024; long curTotal = Runtime.getRuntime().totalMemory() / 1024 / 1024; long curUsed = (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()) / 1024 / 1024; // create labels that show the current memory situation (they will be // updated via Ajax) final Label maxLabel = new Label("max_memory_label", String.valueOf(curMax)); final Label totalLabel = new Label("total_memory_label", String.valueOf(curTotal)); final Label usedLabel = new Label("used_memory_label", String.valueOf(curUsed)); maxLabel.setOutputMarkupId(true); totalLabel.setOutputMarkupId(true); usedLabel.setOutputMarkupId(true); // create a container that redraws itself every second WebMarkupContainer redrawContainer = new WebMarkupContainer("redraw_container"); redrawContainer.add(new AjaxSelfUpdatingTimerBehavior(Duration.seconds(1)) { private static final long serialVersionUID = -5579424950201876034L; /** * These arrays store the memory values of the last 61 seconds (one * second more, because the chart goes from 0 to 60) */ private final long[] maxMemory = new long[61]; private final long[] totalMemory = new long[61]; private final long[] usedMemory = new long[61]; /** * Shifts all values in the given array to the right and sets the * first entry to the given value * * @param arr the array to shift * @param val the new value to insert at position 0 */ private void updateArray(long[] arr, long val) { System.arraycopy(arr, 0, arr, 1, arr.length - 1); arr[0] = val; } /** * Creates a string that can be used as plotting data for the memory * chart * * @param arr the array that contains the memory values of the last * 61 seconds * @return the plot data string */ private String makePlot(long[] arr) { StringBuffer result = new StringBuffer(); for (int i = 0; i < arr.length; ++i) { if (arr[i] != 0) { if (result.length() > 0) { result.append(","); } result.append("[" + i + "," + arr[i] + "]"); } } return result.toString(); } /** * Gets the maximum value from an array * * @param arr the array * @return the maximum value in <code>arr</code> */ private long getMax(long[] arr) { long result = 0; for (int i = 0; i < arr.length; ++i) { if (arr[i] > result) { result = arr[i]; } } return result; } @Override protected void onPostProcessTarget(final AjaxRequestTarget target) { // get current memory situation long curMax = Runtime.getRuntime().maxMemory() / 1024 / 1024; long curTotal = Runtime.getRuntime().totalMemory() / 1024 / 1024; long curUsed = (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()) / 1024 / 1024; // update plot data of last 61 seconds updateArray(totalMemory, curTotal); updateArray(usedMemory, curUsed); // create plot data string String total = makePlot(totalMemory); String free = makePlot(usedMemory); // calculate the maximum for the chart's y axis (+ 50 MB) long ymax = getMax(totalMemory) + 50; // reset labels maxLabel.setDefaultModelObject(String.valueOf(curMax)); totalLabel.setDefaultModelObject(String.valueOf(curTotal)); usedLabel.setDefaultModelObject(String.valueOf(curUsed)); target.add(maxLabel); target.add(totalLabel); target.add(usedLabel); // redraw chart target.appendJavaScript("chart_plot.axes.xaxis.max = " + (maxMemory.length - 1) + ";" + "chart_plot.axes.yaxis.max = " + ymax + ";" + "chart_plot.series[0].data = [" + total + "];" + "chart_plot.series[1].data = [" + free + "];" + "chart_plot.replot();"); } }); redrawContainer.add(maxLabel); redrawContainer.add(totalLabel); redrawContainer.add(usedLabel); add(redrawContainer); // add a button that performs garbage collection AjaxFallbackLink<Object> performGC = new AjaxFallbackLink<Object>("perform-gc") { private static final long serialVersionUID = -1411055574233411598L; @Override public void onClick(AjaxRequestTarget target) { System.gc(); } }; redrawContainer.add(performGC); } @Override public void renderHead(IHeaderResponse response) { super.renderHead(response); response.render(JavaScriptHeaderItem .forReference(new JQueryPluginResourceReference(MemoryPanel.class, "jquery.jqplot.min.js"))); response.render( CssHeaderItem.forReference(new CssResourceReference(MemoryPanel.class, "jquery.jqplot.min.css"))); response.render( JavaScriptHeaderItem.forReference(new JavaScriptResourceReference(MemoryPanel.class, "update.js"))); } }