1.类中方法
引入必要的包：

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletRequest;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.ChartFactory;
import org.jfree.data.general.DefaultPieDataset;
import org.jfree.chart.plot.PiePlot;
import org.jfree.chart.ChartRenderingInfo;
import org.jfree.chart.entity.StandardEntityCollection;
import org.jfree.chart.servlet.ServletUtilities;


int n = orgCourseList.size();//List的长度
int[] Num = new int[n];//存放人数
String[] orgName = new String[n];//存放机构名称
String title = "参加人数统计图";

for (int i = 0; i < n; i++) {
RepVteachStatic temp = new RepVteachStatic();//临时存放对象，视情况可变。RepVteachStatic是一个DTO（数据传输对象）
temp = (RepVteachStatic) orgCourseList.get(i);//取得List中的对象
int personNum = repVteachStaticService.getOrgCoursePersonNum(temp);
//查询出参加人数
Num[i] = personNum;
orgName[i] = temp.getOrg_name();
}
getOrgCoursePieChart(Num, orgName, title);//用三个参数调用图表生成方法

图表生成方法：

public void getOrgCoursePieChart(int[] Num, String[] orgName, String title) {

        DefaultPieDataset data = new DefaultPieDataset();

        for (int i = 0, n = Num.length; i < n; i++) {
            data.setValue(orgName[i], Num[i]);
        }

        JFreeChart chart = ChartFactory.createPieChart3D(title, data, true,false, false);
        chart.setBackgroundPaint(java.awt.Color.green);
        ChartRenderingInfo info = new ChartRenderingInfo(
                new StandardEntityCollection());
        try {         
HttpSession session = ActionContext.getActionContext().getRequest()
.getSession();//取session对象，视情况取法会有变化
              HttpServletRequest request = ActionContext.getActionContext().getRequest();
//取request对象，视情况取法会有变化
              String filename = ServletUtilities.saveChartAsPNG(chart, 500, 300,info, session);

            graphURL = request.getContextPath()
                    + "/servlet/DisplayChart?filename=" + filename;
            }catch (Exception e) {}
}

2.页面

<img src="<bean:writename="repVteachStaticBean" property="graphURL"/>" >