Java tutorial
/* * NOTE: This copyright does *not* cover user programs that use HQ * program services by normal system calls through the application * program interfaces provided as part of the Hyperic Plug-in Development * Kit or the Hyperic Client Development Kit - this is merely considered * normal use of the program, and does *not* fall under the heading of * "derived work". * * Copyright (C) [2004, 2005, 2006], Hyperic, Inc. * This file is part of HQ. * * HQ is free software; you can redistribute it and/or modify * it under the terms version 2 of the GNU General Public License as * published by the Free Software Foundation. This program is distributed * in the hope that it will be useful, but WITHOUT ANY WARRANTY; without * even the implied warranty of MERCHANTABILITY or FITNESS FOR A * PARTICULAR PURPOSE. See the GNU General Public License for more * details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 * USA. */ package org.hyperic.hq.ui.servlet; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * <p>This servlet returns a response that contains the binary data of * an image (JPEG or PNG) that can be viewed in a web browser.</p> * * <p>The navigation map servlet takes the following parameters (any * applicable defaults are in <b>bold</b> and required parameters are * in <i>italics</i>):</p> * * <table border="1"> * <tr><th> key </th><th> value </th></tr> * <tr><td> imageFormat </td><td> (<b>png</b> | jpeg) </td></tr> * <tr><td> imageWidth </td><td> <integer <b>(700)</b>> </td></tr> * <tr><td> imageHeight </td><td> <integer <b>(350)</b>> </td></tr> * </table> * */ public abstract class ImageServlet extends ParameterizedServlet { /** Request parameter for image format. */ public static final String IMAGE_FORMAT_PARAM = "imageFormat"; /** Request parameter value representing a PNG image. */ public static final String IMAGE_FORMAT_PNG = "png"; /** Request parameter value representing a JPEG image. */ public static final String IMAGE_FORMAT_JPEG = "jpeg"; private static final String[] VALID_IMAGE_FORMATS = { IMAGE_FORMAT_PNG, IMAGE_FORMAT_JPEG }; /** Request parameter for image width. */ public static final String IMAGE_WIDTH_PARAM = "imageWidth"; /** Default image width. */ public static final int IMAGE_WIDTH_DEFAULT = 700; /** Request parameter for image height. */ public static final String IMAGE_HEIGHT_PARAM = "imageHeight"; /** Default image height. */ public static final int IMAGE_HEIGHT_DEFAULT = 350; // member data private Log log = LogFactory.getLog(ImageServlet.class.getName()); public ImageServlet() { } public void init() { if (log.isDebugEnabled()) { log.debug("java.awt.headless=" + System.getProperty("java.awt.headless")); } } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException { try { // parse the parameters log.debug("Parsing parameters."); parseParameters(request); // image format String imageFormat = parseStringParameter(request, IMAGE_FORMAT_PARAM, getDefaultImageFormat(), VALID_IMAGE_FORMATS); if (log.isDebugEnabled()) { StringBuffer sb = new StringBuffer("Parameters:"); sb.append("\n\t"); sb.append(IMAGE_FORMAT_PARAM).append(": ").append(imageFormat); log.debug(sb.toString()); } Object imgObj = createImage(request); // render the chart log.debug("Rendering image."); ServletOutputStream out = response.getOutputStream(); if (imageFormat.equals(IMAGE_FORMAT_PNG)) { response.setContentType("image/png"); renderPngImage(out, imgObj); } else { response.setContentType("image/jpeg"); renderJpegImage(out, imgObj); } out.flush(); } catch (IOException e) { // it's okay to ignore this one log.debug("Error writing image to response.", e); } catch (Exception e) { log.error("Unknown error.", e); throw new ServletException("Unknown error.", e); } } /** * Create the image being rendered. * * @param request the servlet request */ protected abstract Object createImage(HttpServletRequest request) throws ServletException; /** * Render a PNG version of the image into the output stream. * * @param out the output stream */ protected abstract void renderPngImage(ServletOutputStream out, Object imgObj) throws IOException; /** * Render a JPEG version of the image into the output stream. * * @param out the output stream */ protected abstract void renderJpegImage(ServletOutputStream out, Object imgObj) throws IOException; /** * This method will be called automatically by the ImageServlet. * It should handle the parsing and error-checking of any specific * parameters for the chart being rendered. * * @param request the HTTP request object */ protected abstract void parseParameters(HttpServletRequest request); /** * Return the image height. * @param request TODO * * @return the height of the image * @see <code>{@link IMAGE_HEIGHT_DEFAULT}</code> */ protected int getImageHeight(HttpServletRequest request) { return parseIntParameter(request, IMAGE_HEIGHT_PARAM, getDefaultImageHeight()); } /** * Return the image width. * @param request TODO * * @return the width of the image * @see <code>{@link IMAGE_WIDTH_DEFAULT}</code> */ protected int getImageWidth(HttpServletRequest request) { return parseIntParameter(request, IMAGE_WIDTH_PARAM, getDefaultImageWidth()); } /** * Return the default <code>imageFormat</code>. */ protected String getDefaultImageFormat() { return IMAGE_FORMAT_PNG; } /** * Return the default <code>imageWidth</code>. */ protected int getDefaultImageWidth() { return IMAGE_WIDTH_DEFAULT; } /** * Return the default <code>imageHeight</code>. */ protected int getDefaultImageHeight() { return IMAGE_HEIGHT_DEFAULT; } } // EOF