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Java 列印與列印預覽機制完整實作範例

編輯：SQL Server 2008

前言

在 Java 桌面應用程式開發中，列印功能是常見需求。本文提供一個完整的範例，展示如何使用 java.awt.print 套件實作 JTextArea 元件的列印與列印預覽功能，包含分頁計算、頁首顯示、滑鼠翻頁互動等核心機制。

核心架構設計

範例採用 Printable 介面實作列印邏輯，主要類別 PrintUIComponent 繼承 JPanel 並實作 ActionListener 與 Printable。內部包含兩個巢狀類別：PreviewArea 負責預覽區域繪製，Header 處理頁碼顯示。

關鍵技術點解析

1. 列印分頁邏輯

在 print() 方法中，透過 FontMetrics 計算每行高度，依據 PageFormat 可列印區域高度推算每頁容納行數，建立 pageBreaks 陣列記錄分頁位置：

int linesPerPage = (int) (pageFormat.getImageableHeight() / lineHeight);
int numBreaks = (textLines.length - 1) / linesPerPage;
pageBreaks = new int[numBreaks];
for (int b = 0; b < numBreaks; b++) {
    pageBreaks[b] = (b + 1) * linesPerPage;
}

2. 列印預覽對話框

createAndShowPreviewDialog() 建立模態對話框，包含 PreviewArea（繪製頁面內容）與 Header（顯示頁碼導航）。PreviewArea 繼承 Component，覆寫 paint() 呼叫主類別的 print() 方法繪製指定頁面。

3. 滑鼠翻頁互動

PreviewAreaMouseAdapter 處理滑鼠點擊事件：左鍵下一頁、右鍵上一頁，透過更新 pageIndex 並呼叫 repaint() 實現翻頁效果。

完整程式碼

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.print.PageFormat;
import java.awt.print.Printable;
import java.awt.print.PrinterException;
import java.awt.print.PrinterJob;

import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;

/**
 * 使用原始分頁方式渲染 JTextArea，提供列印預覽機制。
 * 
 * @author Gaowen
 */
public class PrintUIComponent extends JPanel implements ActionListener, Printable {
    private static final long serialVersionUID = 4797002827940419724L;
    private static JFrame frame;
    private JTextArea textAreaToPrint;
    private PrinterJob job;
    private int[] pageBreaks; // 分頁斷點行號陣列
    private String[] textLines;
    private Header header;

    public PrintUIComponent() {
        super(new BorderLayout());
        textAreaToPrint = new JTextArea(50, 20);
        for (int i = 1; i <= 50; i++) {
            textAreaToPrint.append("Line " + i + "\n");
        }
        JScrollPane scrollPane = new JScrollPane(textAreaToPrint);
        scrollPane.setPreferredSize(new Dimension(250, 200));
        add(scrollPane, BorderLayout.CENTER);
        
        JButton printButton = new JButton("列印此 TextArea");
        printButton.setName("printButton");
        printButton.addActionListener(this);
        JButton printPreviewButton = new JButton("列印預覽");
        printPreviewButton.setName("printPreviewButton");
        printPreviewButton.addActionListener(this);
        
        JPanel buttonGroup = new JPanel(new GridLayout(2, 1));
        buttonGroup.add(printButton);
        buttonGroup.add(printPreviewButton);
        add(buttonGroup, BorderLayout.SOUTH);

        /* 初始化 PrinterJob */
        initPrinterJob();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI() {
        frame = new JFrame("列印 UI 範例");
        frame.setContentPane(new PrintUIComponent());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    private void initTextLines() {
        Document doc = textAreaToPrint.getDocument();
        try {
            String text = doc.getText(0, doc.getLength());
            textLines = text.split("\n");
        } catch (BadLocationException e) {
            e.printStackTrace();
        }
    }

    private void initPrinterJob() {
        job = PrinterJob.getPrinterJob();
        job.setJobName("列印 TextArea"); // 顯示在系統列印工作清單
        job.setPrintable(this);
    }

    @Override
    public int print(Graphics graphics, PageFormat pageFormat, int pageIndex)
            throws PrinterException {
        /* 使用 Graphics 副本避免影響原始物件 */
        Graphics2D g2 = (Graphics2D) graphics.create();

        /* 計算分頁斷點 */
        Font font = new Font("Serif", Font.PLAIN, 12);
        FontMetrics metrics = g2.getFontMetrics(font);
        int lineHeight = metrics.getHeight();
        if (pageBreaks == null) {
            initTextLines();
            int linesPerPage = (int) (pageFormat.getImageableHeight() / lineHeight);
            int numBreaks = (textLines.length - 1) / linesPerPage;
            pageBreaks = new int[numBreaks];
            for (int b = 0; b < numBreaks; b++) {
                pageBreaks[b] = (b + 1) * linesPerPage;
            }
        }

        /* 判斷是否超出頁數範圍 */
        if (pageIndex > pageBreaks.length) {
            return NO_SUCH_PAGE;
        }

        /* 平移座標至可列印區域原點 */
        g2.translate(pageFormat.getImageableX(), pageFormat.getImageableY());

        /* 繪製當前頁面的每一行文字 */
        int y = 0;
        int start = (pageIndex == 0) ? 0 : pageBreaks[pageIndex - 1];
        int end = (pageIndex == pageBreaks.length) ? textLines.length : pageBreaks[pageIndex];
        for (int line = start; line < end; line++) {
            y += lineHeight;
            g2.drawString(textLines[line], 0, y);
        }

        /* 釋放 Graphics 資源 */
        g2.dispose();

        /* 回傳頁面存在旗標 */
        return PAGE_EXISTS;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        Object actionEventSource = e.getSource();
        if (actionEventSource instanceof JButton) {
            JButton button = (JButton) actionEventSource;
            if (button.getName().equals("printButton")) {
                pageBreaks = null; // 重置分頁
                boolean ok = job.printDialog();
                if (ok) {
                    try {
                        job.print();
                    } catch (PrinterException ex) {
                        ex.printStackTrace();
                    }
                }
            } else if (button.getName().equals("printPreviewButton")) {
                pageBreaks = null; // 重置分頁
                createAndShowPreviewDialog();
            }
        }
    }

    private void createAndShowPreviewDialog() {
        JDialog previewDialog = new JDialog(frame, "列印預覽對話框", true);
        JPanel contentPane = new JPanel(new BorderLayout());
        PreviewArea previewArea = new PreviewArea();
        previewArea.addMouseListener(new PreviewAreaMouseAdapter(previewArea));
        JScrollPane scrollPane = new JScrollPane(previewArea);
        contentPane.add(scrollPane, BorderLayout.CENTER);
        header = new Header(previewArea);
        contentPane.add(header, BorderLayout.NORTH);
        previewDialog.setContentPane(contentPane);
        previewDialog.setSize(600, 600);
        previewDialog.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        previewDialog.setVisible(true);
    }

    private class Header extends Component {
        private static final long serialVersionUID = -1741188309769027249L;
        private PreviewArea previewArea;
        private boolean paintable;

        private Header(PreviewArea previewArea) {
            this.previewArea = previewArea;
        }

        private void setPaintable(boolean paintable) {
            this.paintable = paintable;
        }

        @Override
        public void paint(Graphics g) {
            if (paintable) {
                g.setColor(Color.GRAY);
                g.drawString(
                    String.valueOf(previewArea.getPageIndex() + 1)
                    + "/"
                    + String.valueOf(pageBreaks.length + 1)
                    + " 頁 (左鍵下一頁；右鍵上一頁)",
                    10, 15);
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(super.getPreferredSize().width, 20);
        }
    }

    private class PreviewArea extends Component {
        private static final long serialVersionUID = -6384174997251439843L;
        private PageFormat pageFormat;
        private int pageIndex;
        private int w;
        private int h;
        private final int marginX = 10;
        private final int marginY = 20;

        private PreviewArea() {
            pageFormat = job.pageDialog(job.defaultPage());
            pageIndex = 0;
            w = (int) pageFormat.getWidth();
            h = (int) pageFormat.getHeight();
        }

        private int getPageIndex() {
            return pageIndex;
        }

        private void setPageIndex(int pageIndex) {
            this.pageIndex = pageIndex;
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(w + 2 * marginX, h + 2 * marginY);
        }

        @Override
        public void paint(Graphics g) {
            Graphics2D g2 = (Graphics2D) g.create();
            g2.translate(marginX, marginY);
            g2.drawRect(0, 0, w, h);
            int ix = (int) (pageFormat.getImageableX() - 1);
            int iy = (int) (pageFormat.getImageableY() - 1);
            int iw = (int) (pageFormat.getImageableWidth() + 1);
            int ih = (int) (pageFormat.getImageableHeight() + 1);
            g2.setStroke(new BasicStroke(1f, BasicStroke.CAP_ROUND,
                    BasicStroke.JOIN_ROUND, 10f, new float[] { 5, 5 }, 0f));
            g2.drawRect(ix, iy, iw, ih);
            try {
                PrintUIComponent.this.print(g2, pageFormat, pageIndex);
            } catch (PrinterException e) {
                e.printStackTrace();
            }
            g2.dispose();
            header.setPaintable(true);
            header.repaint();
        }
    }

    private class PreviewAreaMouseAdapter extends MouseAdapter {
        private PreviewArea previewArea;

        private PreviewAreaMouseAdapter(PreviewArea previewArea) {
            this.previewArea = previewArea;
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            int currentIndex = previewArea.getPageIndex();
            if (e.getButton() == MouseEvent.BUTTON1) {
                /* 下一頁 */
                if (currentIndex < pageBreaks.length) {
                    previewArea.setPageIndex(currentIndex + 1);
                    previewArea.repaint();
                }
            } else if (e.getButton() == MouseEvent.BUTTON3) {
                /* 上一頁 */
                if (currentIndex > 0) {
                    previewArea.setPageIndex(currentIndex - 1);
                    previewArea.repaint();
                }
            }
        }
    }
}

其他列印方式補充

除了本範例的手動分頁實作，Java 還提供其他列印 JTextArea 的方式：

Component.print(Graphics g) 或 Component.printAll(Graphics g)
Component.paint(Graphics g) 或 Component.paintAll(Graphics g)，渲染結果可能略有不同（如 JFrame）
JTable.print() 或 JTextComponent.print() 提供更強大便利的列印機制