JFreeChart—输出区域图

区域图（Area Chart）与折线图类似，但其强调数据之间的变化幅度，能够直观的现实变化的区域。

实现代码：

AreaChartServlet.java

package com.lmb.jfreechart;

import java.awt.Color;
import java.io.IOException;

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.axis.CategoryAxis;
import org.jfree.chart.axis.CategoryLabelPositions;
import org.jfree.chart.plot.CategoryPlot;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.category.CategoryDataset;
import org.jfree.data.category.DefaultCategoryDataset;
import org.jfree.ui.RectangleInsets;

public class AreaChartServlet extends HttpServlet {

    private static final long serialVersionUID = 5852523271721922574L;
    public AreaChartServlet() {
        super();
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 设置返回类型为图片
        response.setContentType("image/png");
        // 获取数据集对象
        CategoryDataset dataset = createDataset();
        // 创建图形对象
        JFreeChart jfreechart = ChartFactory.createAreaChart("08年图书销售量排名",
                "按季度", "销量", dataset, PlotOrientation.VERTICAL, true, true,
                false);
        // 获得图表区域对象
        CategoryPlot categoryplot = (CategoryPlot) jfreechart.getPlot();
        //设置前景色为50%透明
        categoryplot.setForegroundAlpha(0.5F);
        //设置X轴偏移量
        categoryplot.setAxisOffset(new RectangleInsets(5D, 5D, 5D, 5D));
        //设置北景色为浅灰色
        categoryplot.setBackgroundPaint(Color.lightGray);
        //设置显示网格线
        categoryplot.setDomainGridlinesVisible(true);
        //设置网格线为白色
        categoryplot.setDomainGridlinePaint(Color.white);
        //设置显示边界线
        categoryplot.setRangeGridlinesVisible(true);
        //设置显示边界线为白色
        categoryplot.setRangeGridlinePaint(Color.white);
        //获得X轴对象
        CategoryAxis categoryaxis = categoryplot.getDomainAxis();
        //设置X轴标签位置为45度角
        categoryaxis.setCategoryLabelPositions(CategoryLabelPositions.UP_45);
        //设置与X轴的补白为0
        categoryaxis.setLowerMargin(0.0D);
        categoryaxis.setUpperMargin(0.0D);

        // 将图表已数据流的方式返回给客户端
        ChartUtilities.writeChartAsPNG(response.getOutputStream(), jfreechart,
                500, 270);

    }
    /** * 返回数据集 * * @return */
    private static CategoryDataset createDataset() {
        // 时间维度
        String[] category1 = { "第一季度", "第二季度", "第三季度", "第四季度" };
        // 分类维度
        String[] category2 = { "JAVA", "C/C++", "PHP" };
        DefaultCategoryDataset defaultdataset = new DefaultCategoryDataset();
        for (int i = 0; i < category1.length; i++) {
            String category = category1[i];
            for (int j = 0; j < category2.length; j++) {
                String cat = category2[j];
                // 模拟添加数据
                defaultdataset.addValue(DataUtils.getRandomData(), cat, category);
            }
        }
        return defaultdataset;
    }


}

web.xml略。。。

总结：

1、利用CategoryDataset数据集绘制区域图；

2、对应创建区域图的方法是createAreaChart()；

3、利用CategoryAxis对象设置绘制区域的显示方式；