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：
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。