JFreeChart 核心 API 實戰：從數據集到專業級圖表生成

核心類架構

ChartFactory (工廠)
    ↓ createXxxChart()
JFreeChart (圖表容器)
    ├─ Title (標題)
    ├─ Legend (圖例)
    └─ Plot (繪圖區) → CategoryPlot / XYPlot / PiePlot
         ├─ Domain Axis (域軸/橫軸)
         ├─ Range Axis (范圍軸/縱軸)
         └─ Renderer (渲染器) → LineAndShapeRenderer / BarRenderer ...

完整獨立運行 Demo (含文件輸出 & Web 臨時文件)

public class ChartDemo {
    public static void main(String[] args) {
        ChartDemo demo = new ChartDemo();
        JFreeChart chart = demo.createLineChart();
        demo.saveAsFile(chart, "C:/temp/LineChart.jpg"); // 本地文件
        // String fileName = demo.saveAsTemp(chart, request.getSession(), response.getWriter()); // Web 臨時文件
    }

    /** 創建雙序列折線圖 */
    public JFreeChart createLineChart() {
        // 1. 數據集
        DefaultCategoryDataset dataset = new DefaultCategoryDataset();
        String s1 = "東京", s2 = "紐約";
        String[] types = {"1月","2月","3月","4月","5月","6月","7月"};
        double[][] data = {
            {1.0, 4.0, 3.0, 5.0, 5.0, 7.0, 7.0}, // 東京
            {5.0, 7.0, 6.0, 8.0, 4.0, 4.0, 2.0}  // 紐約
        };
        for (int i = 0; i < types.length; i++) {
            dataset.addValue(data[0][i], s1, types[i]);
            dataset.addValue(data[1][i], s2, types[i]);
        }

        // 2. 工廠創建
        JFreeChart chart = ChartFactory.createLineChart(
            "月均溫度對比", "月份", "溫度 (°C)", dataset,
            PlotOrientation.VERTICAL, true, true, false
        );

        // 3. 圖表級美化
        chart.setBackgroundPaint(Color.WHITE);
        chart.getLegend().setPosition(RectangleEdge.RIGHT);
        chart.getTitle().setFont(new Font("微軟雅黑", Font.BOLD, 16));
        chart.getLegend().setItemFont(new Font("微軟雅黑", Font.PLAIN, 12));

        // 4. Plot 級美化
        CategoryPlot plot = chart.getCategoryPlot();
        plot.setBackgroundPaint(Color.LIGHT_GRAY);
        plot.setDomainGridlinesVisible(true);
        plot.setRangeGridlinesVisible(true);
        plot.setDomainGridlinePaint(Color.WHITE);
        plot.setRangeGridlinePaint(Color.WHITE);
        plot.setAxisOffset(new RectangleInsets(0, 0, 0, 10)); // 與軸留白

        // 5. 域軸 (橫軸)
        CategoryAxis domain = plot.getDomainAxis();
        domain.setCategoryLabelPositions(CategoryLabelPositions.UP_45); // 45° 傾斜
        domain.setTickLabelFont(new Font("微軟雅黑", Font.PLAIN, 11));
        domain.setLabelFont(new Font("微軟雅黑", Font.BOLD, 13));

        // 6. 范圍軸 (縱軸)
        NumberAxis range = (NumberAxis) plot.getRangeAxis();
        range.setStandardTickUnits(NumberAxis.createIntegerTickUnits());
        range.setAutoRangeIncludesZero(true);
        range.setTickLabelFont(new Font("微軟雅黑", Font.PLAIN, 11));
        range.setLabelFont(new Font("微軟雅黑", Font.BOLD, 13));
        range.setUpperBound(10); // 根據數據調整

        // 7. 渲染器 (線條/形狀/標籤)
        LineAndShapeRenderer renderer = (LineAndShapeRenderer) plot.getRenderer();
        renderer.setShapesVisible(true); // 顯示數據點
        renderer.setSeriesStroke(0, new BasicStroke(2f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND, 1f, new float[]{10f, 6f}, 0f)); // 虛線
        renderer.setSeriesStroke(1, new BasicStroke(2f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND, 1f, new float[]{6f, 6f}, 0f));
        renderer.setBaseItemLabelsVisible(true);
        renderer.setBaseItemLabelGenerator(new StandardCategoryItemLabelGenerator());
        renderer.setBaseItemLabelFont(new Font("微軟雅黑", Font.PLAIN, 10));

        return chart;
    }

    /** 保存為本地圖片文件 */
    public void saveAsFile(JFreeChart chart, String path) {
        try {
            ChartUtilities.saveChartAsJPEG(new File(path), chart, 800, 600);
            // 或 saveChartAsPNG
        } catch (IOException e) { throw new RuntimeException(e); }
    }

    /** Web 環境保存為 Session 臨時文件，返回文件名供 DisplayChart Servlet 使用 */
    public String saveAsTemp(JFreeChart chart, HttpSession session, PrintWriter out) {
        try {
            ChartRenderingInfo info = new ChartRenderingInfo(new StandardEntityCollection());
            String fileName = ServletUtilities.saveChartAsPNG(chart, 700, 450, info, session);
            ChartUtilities.writeImageMap(out, fileName, info, false); // 可選：圖片映射 (熱區)
            out.flush();
            return fileName;
        } catch (IOException e) { throw new RuntimeException(e); }
    }
}

JSP/Web 調用示例

<%@ page import="com.demo.ChartDemo" %>
<%
    ChartDemo demo = new ChartDemo();
    JFreeChart chart = demo.createLineChart();
    String fileName = demo.saveAsTemp(chart, session, new PrintWriter(out));
    String graphUrl = request.getContextPath() + "/DisplayChart?filename=" + fileName;
%>
<img src="<%= graphUrl %>" width="700" height="450" border="0" usemap="<%= fileName %>" />

關鍵 API 速查表

中文亂碼終極解決

所有 setFont 統一指定支持中文的字體（微軟雅黑、SimHei、Noto Sans CJK SC）。
Linux 服務器必須安裝字體包：yum install google-noto-sans-cjk-ttc-fonts 或 apt install fonts-noto-cjk。