Java: How to extract text from selected area from PDF file using iText?

You have a very interesting question and a difficult project. This "answer" may provide some useful ideas, but it is not a complete solution.

You can use what is called a glass panel to paint over other components.

Most importantly, in my opinion, you need to decide which libraries are optimal for your project. the iText library is very good and provides all sorts of PDF functions like the text extraction you show in your question.

But as far as I know, there is no support for viewing PDF files in iText. You can use a library like ICEpdf (see this example ). It would be really nice if ICEpdf could also support text extraction, so you could use one library instead of ICEpdf working with iText or OCR (and handle issues like scaling pdf to ICEpdf and compensating for that when you get text).

I'm not sure if you can extract text using ICEpdf, so iText is currently still being used to do this in the code example below:

// File ExtractSelectionFromPdf.java

import com.itextpdf.text.Rectangle;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.parser.*;

import java.awt.Container;
import java.awt.Point;
import java.io.IOException;
import javax.swing.*;

public class ExtractSelectionFromPdf {
    private static String filePath = "[file path to a pdf file]";

    private PdfViewer pdfViewer;

    public static void main(final String[] arguments) {
        SwingUtilities.invokeLater(() -> new ExtractSelectionFromPdf().launchGUI());
    }

    private void launchGUI() {
        final JFrame frame = new JFrame("Extract selected text from a pdf");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        final Container contentPane = frame.getContentPane();

        pdfViewer = new PdfViewer();
        contentPane.add(pdfViewer);

        pdfViewer.openDocument(filePath);

        final CustomGlassPane customGlassPane = new CustomGlassPane(this, contentPane);
        frame.setGlassPane(customGlassPane);
        customGlassPane.setVisible(true);

        frame.setBounds(60, 10, 1800, 1000);
        frame.setVisible(true);
    }

    public void handleSelection(final Point topLeft, final Point bottomRight) {
        final int width = bottomRight.x - topLeft.x;
        final int height = bottomRight.y - topLeft.x;
        final String text = parsePdf(topLeft.x, topLeft.y, width, height, filePath);
        System.out.println("text: " + text);
    }

    public String parsePdf(final int x, final int y, final int width, final int height, 
                           final String pdfFilePath) {
        String text = null;

        try {
            final PdfReader pdfReader = new PdfReader(pdfFilePath);
            final int pageNumber = pdfViewer.getCurrentPageNumber() + 1;
            System.out.println("Page number: " + pageNumber);
            final Rectangle selection = new Rectangle(x, y, width, height);
            final RenderFilter renderFilter = new RegionTextRenderFilter(selection);
            final LocationTextExtractionStrategy delegate 
                    = new LocationTextExtractionStrategy();
            final TextExtractionStrategy extractionStrategy 
                    = new FilteredTextRenderListener(delegate, renderFilter);
            text = PdfTextExtractor.getTextFromPage(pdfReader, pageNumber, 
                                                    extractionStrategy);
            pdfReader.close();
        } catch (final IOException e) {
            e.printStackTrace();
        }

        return text;
    }
}


// File PdfViewer.java

import java.util.ResourceBundle;
import javax.swing.*;
import org.icepdf.ri.common.*;
import org.icepdf.ri.common.views.DocumentViewController;
import org.icepdf.ri.util.PropertiesManager;

public class PdfViewer extends JPanel {
    private final SwingController controller;

    public PdfViewer() {
        controller = new SwingController();
        controller.setIsEmbeddedComponent(true);

        final String bundleName = PropertiesManager.DEFAULT_MESSAGE_BUNDLE;
        final ResourceBundle messageBundle = ResourceBundle.getBundle(bundleName);
        final Properties systemProperties = System.getProperties();
        final PropertiesManager properties = new PropertiesManager(systemProperties,
                                                                   messageBundle);

        properties.set(PropertiesManager.PROPERTY_DEFAULT_ZOOM_LEVEL, "1");

        final SwingViewBuilder factory = new SwingViewBuilder(controller, properties);

        final DocumentViewController viewController 
                = controller.getDocumentViewController();
        viewController.setAnnotationCallback(new MyAnnotationCallback(viewController));

        final JScrollPane scrollPane = new JScrollPane(factory.buildViewerPanel());
        final int horizontalPolicy = ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
        final int verticalPolicy = ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
        scrollPane.setHorizontalScrollBarPolicy(horizontalPolicy);
        scrollPane.setVerticalScrollBarPolicy(verticalPolicy);
        add(scrollPane);
    }

    public void openDocument(final String filePath) {
        controller.openDocument(filePath);
    }

    public int getCurrentPageNumber() {
        return controller.getCurrentPageNumber();
    }
}


// File CustomGlassPane.java

import java.awt.*;
import javax.swing.JComponent;

public class CustomGlassPane extends JComponent {
    private Point topLeftPoint;
    private Point bottomRightPoint;

    public CustomGlassPane(final ExtractSelectionFromPdf extractSelectionFromPdf, 
                           final Container contentPane) {
        final MouseEventsListener listener 
                = new MouseEventsListener(extractSelectionFromPdf, this, contentPane);
        addMouseListener(listener);
        addMouseMotionListener(listener);
    }

    public void setSelection(final Point topLeftPoint, final Point bottomRightPoint) {
        this.topLeftPoint = topLeftPoint;
        this.bottomRightPoint = bottomRightPoint;
    }

    protected void paintComponent(final Graphics graphics) {
        if (topLeftPoint != null && bottomRightPoint != null) {
            graphics.setColor(Color.BLACK);
            graphics.drawRect(topLeftPoint.x, 
                              topLeftPoint.y,
                              bottomRightPoint.x - topLeftPoint.x, 
                              bottomRightPoint.y - topLeftPoint.y);
        }
    }
}


// File MouseEventsListener.java

import java.awt.*;
import java.awt.event.MouseEvent;
import javax.swing.SwingUtilities;
import javax.swing.event.MouseInputAdapter;

public class MouseEventsListener extends MouseInputAdapter {
    private ExtractSelectionFromPdf extractSelectionFromPdf;
    private CustomGlassPane customGlassPane;
    private Container contentPane;
    private Point topLeftPoint;
    private Point bottomRightPoint;

    public MouseEventsListener(final ExtractSelectionFromPdf extractSelectionFromPdf,
                               final CustomGlassPane customGlassPane,
                               final Container contentPane) {
        this.extractSelectionFromPdf = extractSelectionFromPdf;
        this.customGlassPane = customGlassPane;
        this.contentPane = contentPane;
    }

    public void mousePressed(final MouseEvent mouseEvent) {
        topLeftPoint = mouseEvent.getPoint();

        redispatchMouseEvent(mouseEvent);
    }

    public void mouseDragged(final MouseEvent mouseEvent) {
        bottomRightPoint = mouseEvent.getPoint();

        redispatchMouseEvent(mouseEvent, topLeftPoint != null, false);
    }

    public void mouseReleased(final MouseEvent mouseEvent) {
        bottomRightPoint = mouseEvent.getPoint();

        redispatchMouseEvent(mouseEvent, true, true);
    }

    public void mouseMoved(final MouseEvent mouseEvent) {
        redispatchMouseEvent(mouseEvent);
    }

    public void mouseClicked(final MouseEvent mouseEvent) {
        redispatchMouseEvent(mouseEvent);
    }

    public void mouseEntered(final MouseEvent mouseEvent) {
        redispatchMouseEvent(mouseEvent);
    }

    public void mouseExited(final MouseEvent mouseEvent) {
        redispatchMouseEvent(mouseEvent);
    }

    private void redispatchMouseEvent(final MouseEvent mouseEvent) {
        redispatchMouseEvent(mouseEvent, false, false);
    }

    private void redispatchMouseEvent(final MouseEvent mouseEvent, 
                                      final boolean repaint,
                                      final boolean extract) {
        final Point glassPanePoint = mouseEvent.getPoint();
        final Point containerPoint = SwingUtilities.convertPoint(customGlassPane, 
                                                                 glassPanePoint, 
                                                                 contentPane);

        if (containerPoint.y >= 0) {
            final Component component
                    = SwingUtilities.getDeepestComponentAt(contentPane,
                                                           containerPoint.x,
                                                           containerPoint.y);

            if (component != null) {
                final Point componentPoint 
                        = SwingUtilities.convertPoint(customGlassPane, 
                                                      glassPanePoint,
                                                      component);

                // Forward events to the component under the glass pane.
                component.dispatchEvent(new MouseEvent(component,
                                                       mouseEvent.getID(),
                                                       mouseEvent.getWhen(),
                                                       mouseEvent.getModifiers(),
                                                       componentPoint.x,
                                                       componentPoint.y,
                                                       mouseEvent.getClickCount(),
                                                       mouseEvent.isPopupTrigger()));
            }
        }

        // Update the glass pane if requested.
        if (repaint) {
            if (extract) {
                extractSelectionFromPdf.handleSelection(topLeftPoint, bottomRightPoint);

                topLeftPoint = null;
                bottomRightPoint = null;
            }

            customGlassPane.setSelection(topLeftPoint, bottomRightPoint);
            customGlassPane.repaint();
        }
    }
}

      

        
        
        
      

    

Part of the glass pane above the code has been inspired GlassPaneDemo

example .

Known remaining issues in the code above:

• For some reason, the scroll down button to view PDF files must be clicked once before the Up / Down and Up / Down Arrow keys work.
• currently the text that is actually being extracted appears to be below the selected rectangle.