19.5 在HMTL页面种嵌入图表 · Java 开源项目中文文档

## 19.5 在HMTL页面种嵌入图表在HTML页面中嵌入servlet产生的图表图像也是可以的，下面实例ServletDemo2演示了这一特征。ServletDemo2实例处理一个HTML页面的请求，该HTML引用了另一个servlet（ServletDemo2ChartGenerator），引用的这个servlet返回了一个图表产生的PNG图像。最终的结果就是将图表嵌入到了一个HTML中，如图19.2所示： ![](img/jfc122184.png) 如图19.2 浏览器中的ServletDemo2 全部代码如下： ``` package demo; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * A basic servlet that generates an HTML page that displays a chart generated * by JFreeChart. * <P> * This servlet uses another servlet (ServletDemo2ChartGenerator) to create a * PNG image for the embedded chart. * <P> * This class is described in the JFreeChart Developer Guide. */ public class ServletDemo2 extends HttpServlet { /** * */ private static final long serialVersionUID = 9024040467697909853L; /** * Creates a new servlet demo. */ public ServletDemo2() { // nothing required } /** * Processes a POST request. * <P> * The chart.html page contains a form for generating the first request, * after that the HTML returned by this servlet contains the same form for * generating subsequent requests. * * @param request * the request. * @param response * the response. * * @throws ServletException * if there is a servlet related problem. * @throws IOException * if there is an I/O problem. */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = new PrintWriter(response.getWriter()); try { String param = request.getParameter("chart"); response.setContentType("text/html"); out.println("<HTML>"); out.println("<HEAD>"); out.println("<TITLE>JFreeChart Servlet Demo 2</TITLE>"); out.println("</HEAD>"); out.println("<BODY>"); out.println("<H2>JFreeChart Servlet Demo</H2>"); out.println("<P>"); out.println("Please choose a chart type:"); out.println("<FORM ACTION=\"ServletDemo2\" METHOD=POST>"); String pieChecked = (param.equals("pie") ? " CHECKED" : ""); String barChecked = (param.equals("bar") ? " CHECKED" : ""); String timeChecked = (param.equals("time") ? " CHECKED" : ""); out.println("<INPUT TYPE=\"radio\" NAME=\"chart\" VALUE=\"pie\"" + pieChecked + "> Pie Chart"); out.println("<INPUT TYPE=\"radio\" NAME=\"chart\" VALUE=\"bar\"" + barChecked + "> Bar Chart"); out.println("<INPUT TYPE=\"radio\" NAME=\"chart\" VALUE=\"time\"" + timeChecked + "> Time Series Chart"); out.println("<P>"); out.println("<INPUT TYPE=\"submit\" VALUE=\"Generate Chart\">"); out.println("</FORM>"); out.println("<P>"); out.println("<IMG SRC=\"ServletDemo2ChartGenerator?type=" + param + "\" BORDER=1 WIDTH=400 HEIGHT=300/>"); out.println("</BODY>"); out.println("</HTML>"); out.flush(); out.close(); } catch (Exception e) { System.err.println(e.toString()); } finally { out.close(); } } } ``` 注意该代码是如何从响应的参数获得一个引用的，而不是上面实例中的一个输出流。愿意是因为该servlet将返回HTML文本，与前章返回的二进制数据（一个PNG图片）不同。响应的类型设置成为text/html格式，因为servlet返回的是HTML文件。重要的一点就是HTML引用另一个servlet（ServletDemo2ChartGenerator）中的<IMG>标签，ServletDemo2ChartGenerator创建了必要的图表图片。HTML使用<FORM>元素来建立图表参数控制着实际图表的返回。下面是ServletDemo2ChartGenerator的全部代码： ``` package demo; import java.io.IOException; import java.io.OutputStream; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.jfree.chart.ChartFactory; import org.jfree.chart.ChartUtilities; import org.jfree.chart.JFreeChart; import org.jfree.chart.plot.PlotOrientation; import org.jfree.data.category.DefaultCategoryDataset; import org.jfree.data.general.DefaultPieDataset; import org.jfree.data.time.Day; import org.jfree.data.time.TimeSeries; import org.jfree.data.time.TimeSeriesCollection; import org.jfree.data.xy.XYDataset; import org.jfree.date.SerialDate; /** * A servlet that returns one of three charts as a PNG image file. This servlet * is referenced in the HTML generated by ServletDemo2. * <P> * Three different charts can be generated, controlled by the ’type’ parameter. * The possible values are ’pie’, ’bar’ and ’time’ (for time series). * <P> * This class is described in the JFreeChart Developer Guide. */ public class ServletDemo2ChartGenerator extends HttpServlet { /** * Default constructor. */ public ServletDemo2ChartGenerator() { // nothing required } /** * Process a GET request. * * @param request * the request. * @param response * the response. * * @throws ServletException * if there is a servlet related problem. * @throws IOException * if there is an I/O problem. */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { OutputStream out = response.getOutputStream(); try { String type = request.getParameter("type"); JFreeChart chart = null; if (type.equals("pie")) { chart = createPieChart(); } else if (type.equals("bar")) { chart = createBarChart(); } else if (type.equals("time")) { chart = createTimeSeriesChart(); } if (chart != null) { response.setContentType("image/png"); ChartUtilities.writeChartAsPNG(out, chart, 400, 300); } } catch (Exception e) { System.err.println(e.toString()); } finally { out.close(); } } /** * Creates a sample pie chart. * * @return a pie chart. */ private JFreeChart createPieChart() { // create a dataset... DefaultPieDataset data = new DefaultPieDataset(); data.setValue("One", new Double(43.2)); data.setValue("Two", new Double(10.0)); data.setValue("Three", new Double(27.5)); data.setValue("Four", new Double(17.5)); data.setValue("Five", new Double(11.0)); data.setValue("Six", new Double(19.4)); JFreeChart chart = ChartFactory.createPieChart("Pie Chart", data, true, true, false); return chart; } /** * Creates a sample bar chart. * * @return a bar chart. */ private JFreeChart createBarChart() { DefaultCategoryDataset dataset = new DefaultCategoryDataset(); dataset.addValue(10.0, "S1", "C1"); dataset.addValue(4.0, "S1", "C2"); dataset.addValue(15.0, "S1", "C3"); dataset.addValue(14.0, "S1", "C4"); dataset.addValue(-5.0, "S2", "C1"); dataset.addValue(-7.0, "S2", "C2"); dataset.addValue(14.0, "S2", "C3"); dataset.addValue(-3.0, "S2", "C4"); dataset.addValue(6.0, "S3", "C1"); dataset.addValue(17.0, "S3", "C2"); dataset.addValue(-12.0, "S3", "C3"); dataset.addValue(7.0, "S3", "C4"); dataset.addValue(7.0, "S4", "C1"); dataset.addValue(15.0, "S4", "C2"); dataset.addValue(11.0, "S4", "C3"); dataset.addValue(0.0, "S4", "C4"); dataset.addValue(-8.0, "S5", "C1"); dataset.addValue(-6.0, "S5", "C2"); dataset.addValue(10.0, "S5", "C3"); dataset.addValue(-9.0, "S5", "C4"); dataset.addValue(9.0, "S6", "C1"); dataset.addValue(8.0, "S6", "C2"); dataset.addValue(null, "S6", "C3"); dataset.addValue(6.0, "S6", "C4"); dataset.addValue(-10.0, "S7", "C1"); dataset.addValue(9.0, "S7", "C2"); dataset.addValue(7.0, "S7", "C3"); dataset.addValue(7.0, "S7", "C4"); dataset.addValue(11.0, "S8", "C1"); dataset.addValue(13.0, "S8", "C2"); dataset.addValue(9.0, "S8", "C3"); dataset.addValue(9.0, "S8", "C4"); dataset.addValue(-3.0, "S9", "C1"); dataset.addValue(7.0, "S9", "C2"); dataset.addValue(11.0, "S9", "C3"); dataset.addValue(-10.0, "S9", "C4"); JFreeChart chart = ChartFactory.createBarChart3D("Bar Chart", "Category", "Value", dataset, PlotOrientation.VERTICAL, true, true, false); return chart; } /** * Creates a sample time series chart. * * @return a time series chart. */ private JFreeChart createTimeSeriesChart() { // here we just populate a series with random data... TimeSeries series = new TimeSeries("Random Data"); Day current = new Day(1, SerialDate.JANUARY, 2001); for (int i = 0; i < 100; i++) { series.add(current, Math.random() * 100); current = (Day) current.next(); } XYDataset data = new TimeSeriesCollection(series); JFreeChart chart = ChartFactory.createTimeSeriesChart( "Time Series Chart", "Date", "Rate", data, true, true, false); return chart; } } ``` 下一章讲述servlet的支持文件，与如何部署它们。