kernel.jar is a component in iText Java library to provide low-level functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided together with the JAR file in the binary packge like iText7-Core-7.1.4.zip. You can download it at iText 7 Core Download site.

You can compile it to generate your JAR file, using kernel.pom as the build configuration file.

The source code of kernel-7.1.4.jar is provided below:

⏎ com/itextpdf/kernel/pdf/canvas/parser/listener/LocationTextExtractionStrategy.java

/*

    This file is part of the iText (R) project.
    Copyright (c) 1998-2018 iText Group NV
    Authors: Bruno Lowagie, Paulo Soares, et al.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License version 3
    as published by the Free Software Foundation with the addition of the
    following permission added to Section 15 as permitted in Section 7(a):
    FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
    ITEXT GROUP. ITEXT GROUP DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
    OF THIRD PARTY RIGHTS

    This program is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE.
    See the GNU Affero General Public License for more details.
    You should have received a copy of the GNU Affero General Public License
    along with this program; if not, see http://www.gnu.org/licenses or write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA, 02110-1301 USA, or download the license from the following URL:
    http://itextpdf.com/terms-of-use/

    The interactive user interfaces in modified source and object code versions
    of this program must display Appropriate Legal Notices, as required under
    Section 5 of the GNU Affero General Public License.

    In accordance with Section 7(b) of the GNU Affero General Public License,
    a covered work must retain the producer line in every PDF that is created
    or manipulated using iText.

    You can be released from the requirements of the license by purchasing
    a commercial license. Buying such a license is mandatory as soon as you
    develop commercial activities involving the iText software without
    disclosing the source code of your own applications.
    These activities include: offering paid services to customers as an ASP,
    serving PDFs on the fly in a web application, shipping iText with a closed
    source product.

    For more information, please contact iText Software Corp. at this
    address: sales@itextpdf.com
 */
package com.itextpdf.kernel.pdf.canvas.parser.listener;

import com.itextpdf.kernel.geom.LineSegment;
import com.itextpdf.kernel.geom.Matrix;
import com.itextpdf.kernel.geom.Vector;
import com.itextpdf.kernel.pdf.canvas.CanvasTag;
import com.itextpdf.kernel.pdf.canvas.parser.EventType;
import com.itextpdf.kernel.pdf.canvas.parser.data.IEventData;
import com.itextpdf.kernel.pdf.canvas.parser.data.TextRenderInfo;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class LocationTextExtractionStrategy implements ITextExtractionStrategy {

    /**
     * set to true for debugging
     */
    private static boolean DUMP_STATE = false;

    /**
     * a summary of all found text
     */
    private final List<TextChunk> locationalResult = new ArrayList<>();

    private final ITextChunkLocationStrategy tclStrat;

    private boolean useActualText = false;

    private boolean rightToLeftRunDirection = false;

    private TextRenderInfo lastTextRenderInfo;

    /**
     * Creates a new text extraction renderer.
     */
    public LocationTextExtractionStrategy() {
        this(new ITextChunkLocationStrategy() {
            public ITextChunkLocation createLocation(TextRenderInfo renderInfo, LineSegment baseline) {
                return new TextChunkLocationDefaultImp(baseline.getStartPoint(), baseline.getEndPoint(), renderInfo.getSingleSpaceWidth());
            }
        });
    }

    /**
     * Creates a new text extraction renderer, with a custom strategy for
     * creating new TextChunkLocation objects based on the input of the
     * TextRenderInfo.
     *
     * @param strat the custom strategy
     */
    public LocationTextExtractionStrategy(ITextChunkLocationStrategy strat) {
        tclStrat = strat;
    }

    /**
     * Changes the behavior of text extraction so that if the parameter is set to {@code true},
     * /ActualText marked content property will be used instead of raw decoded bytes.
     * Beware: the logic is not stable yet.
     *
     * @param useActualText true to use /ActualText, false otherwise
     * @return this object
     */
    public LocationTextExtractionStrategy setUseActualText(boolean useActualText) {
        this.useActualText = useActualText;
        return this;
    }

    /**
     * Sets if text flows from left to right or from right to left.
     * Call this method with <code>true</code> argument for extracting Arabic, Hebrew or other
     * text with right-to-left writing direction.
     *
     * @param rightToLeftRunDirection value specifying whether the direction should be right to left
     * @return this object
     */
    public LocationTextExtractionStrategy setRightToLeftRunDirection(boolean rightToLeftRunDirection) {
        this.rightToLeftRunDirection = rightToLeftRunDirection;
        return this;
    }

    /**
     * Gets the value of the property which determines if /ActualText will be used when extracting
     * the text
     *
     * @return true if /ActualText value is used, false otherwise
     */
    public boolean isUseActualText() {
        return useActualText;
    }

    @Override
    public void eventOccurred(IEventData data, EventType type) {
        if (type.equals(EventType.RENDER_TEXT)) {
            TextRenderInfo renderInfo = (TextRenderInfo) data;
            LineSegment segment = renderInfo.getBaseline();
            if (renderInfo.getRise() != 0) {
                // remove the rise from the baseline - we do this because the text from a super/subscript render operations should probably be considered as part of the baseline of the text the super/sub is relative to
                Matrix riseOffsetTransform = new Matrix(0, -renderInfo.getRise());
                segment = segment.transformBy(riseOffsetTransform);
            }

            if (useActualText) {
                CanvasTag lastTagWithActualText = lastTextRenderInfo != null
                        ? findLastTagWithActualText(lastTextRenderInfo.getCanvasTagHierarchy())
                        : null;
                if (lastTagWithActualText != null && lastTagWithActualText == findLastTagWithActualText(renderInfo.getCanvasTagHierarchy())) {
                    // Merge two text pieces, assume they will be in the same line
                    TextChunk lastTextChunk = locationalResult.get(locationalResult.size() - 1);
                    Vector mergedStart = new Vector(Math.min(lastTextChunk.getLocation().getStartLocation().get(0), segment.getStartPoint().get(0)),
                            Math.min(lastTextChunk.getLocation().getStartLocation().get(1), segment.getStartPoint().get(1)),
                            Math.min(lastTextChunk.getLocation().getStartLocation().get(2), segment.getStartPoint().get(2)));
                    Vector mergedEnd = new Vector(Math.max(lastTextChunk.getLocation().getEndLocation().get(0), segment.getEndPoint().get(0)),
                            Math.max(lastTextChunk.getLocation().getEndLocation().get(1), segment.getEndPoint().get(1)),
                            Math.max(lastTextChunk.getLocation().getEndLocation().get(2), segment.getEndPoint().get(2)));
                    TextChunk merged = new TextChunk(lastTextChunk.getText(), tclStrat.createLocation(renderInfo,
                            new LineSegment(mergedStart, mergedEnd)));
                    locationalResult.set(locationalResult.size() - 1, merged);
                } else {
                    String actualText = renderInfo.getActualText();
                    TextChunk tc = new TextChunk(actualText != null ? actualText : renderInfo.getText(),
                            tclStrat.createLocation(renderInfo, segment));
                    locationalResult.add(tc);
                }
            } else {
                TextChunk tc = new TextChunk(renderInfo.getText(), tclStrat.createLocation(renderInfo, segment));
                locationalResult.add(tc);
            }

            lastTextRenderInfo = renderInfo;
        }
    }

    @Override
    public Set<EventType> getSupportedEvents() {
        return null;
    }

    @Override
    public String getResultantText() {
        if (DUMP_STATE) dumpState();

        List<TextChunk> textChunks = new ArrayList<>(locationalResult);
        sortWithMarks(textChunks);

        StringBuilder sb = new StringBuilder();
        TextChunk lastChunk = null;
        for (TextChunk chunk : textChunks) {
            if (lastChunk == null) {
                sb.append(chunk.text);
            } else {
                if (chunk.sameLine(lastChunk)) {
                    // we only insert a blank space if the trailing character of the previous string wasn't a space, and the leading character of the current string isn't a space
                    if (isChunkAtWordBoundary(chunk, lastChunk) && !startsWithSpace(chunk.text) && !endsWithSpace(lastChunk.text)) {
                        sb.append(' ');
                    }

                    sb.append(chunk.text);
                } else {
                    sb.append('\n');
                    sb.append(chunk.text);
                }
            }
            lastChunk = chunk;
        }

        return sb.toString();
    }

    /**
     * Determines if a space character should be inserted between a previous chunk and the current chunk.
     * This method is exposed as a callback so subclasses can fine time the algorithm for determining whether a space should be inserted or not.
     * By default, this method will insert a space if the there is a gap of more than half the font space character width between the end of the
     * previous chunk and the beginning of the current chunk.  It will also indicate that a space is needed if the starting point of the new chunk
     * appears *before* the end of the previous chunk (i.e. overlapping text).
     *
     * @param chunk         the new chunk being evaluated
     * @param previousChunk the chunk that appeared immediately before the current chunk
     * @return true if the two chunks represent different words (i.e. should have a space between them).  False otherwise.
     */
    protected boolean isChunkAtWordBoundary(TextChunk chunk, TextChunk previousChunk) {
        return chunk.getLocation().isAtWordBoundary(previousChunk.getLocation());
    }

    /**
     * Checks if the string starts with a space character, false if the string is empty or starts with a non-space character.
     *
     * @param str the string to be checked
     * @return true if the string starts with a space character, false if the string is empty or starts with a non-space character
     */
    private boolean startsWithSpace(String str) {
        return str.length() != 0 && str.charAt(0) == ' ';
    }

    /**
     * Checks if the string ends with a space character, false if the string is empty or ends with a non-space character
     *
     * @param str the string to be checked
     * @return true if the string ends with a space character, false if the string is empty or ends with a non-space character
     */
    private boolean endsWithSpace(String str) {
        return str.length() != 0 && str.charAt(str.length() - 1) == ' ';
    }

    /**
     * Used for debugging only
     */
    private void dumpState() {
        for (TextChunk location : locationalResult) {
            location.printDiagnostics();
            System.out.println();
        }
    }

    private CanvasTag findLastTagWithActualText(List<CanvasTag> canvasTagHierarchy) {
        CanvasTag lastActualText = null;
        for (CanvasTag tag : canvasTagHierarchy) {
            if (tag.getActualText() != null) {
                lastActualText = tag;
                break;
            }
        }
        return lastActualText;
    }

    private void sortWithMarks(List<TextChunk> textChunks) {
        Map<TextChunk, TextChunkMarks> marks = new HashMap<>();
        List<TextChunk> toSort = new ArrayList<>();

        for (int markInd = 0; markInd < textChunks.size(); markInd++) {
            ITextChunkLocation location = textChunks.get(markInd).getLocation();
            if (location.getStartLocation().equals(location.getEndLocation())) {
                boolean foundBaseToAttachTo = false;
                for (int baseInd = 0; baseInd < textChunks.size(); baseInd++) {
                    if (markInd != baseInd) {
                        ITextChunkLocation baseLocation = textChunks.get(baseInd).getLocation();
                        if (!baseLocation.getStartLocation().equals(baseLocation.getEndLocation()) && TextChunkLocationDefaultImp.containsMark(baseLocation, location)) {
                            TextChunkMarks currentMarks = marks.get(textChunks.get(baseInd));
                            if (currentMarks == null) {
                                currentMarks = new TextChunkMarks();
                                marks.put(textChunks.get(baseInd), currentMarks);
                            }

                            if (markInd < baseInd) {
                                currentMarks.preceding.add(textChunks.get(markInd));
                            } else {
                                currentMarks.succeeding.add(textChunks.get(markInd));
                            }

                            foundBaseToAttachTo = true;
                            break;
                        }
                    }
                }

                if (!foundBaseToAttachTo) {
                    toSort.add(textChunks.get(markInd));
                }
            } else {
                toSort.add(textChunks.get(markInd));
            }
        }

        Collections.sort(toSort, new TextChunkLocationBasedComparator(new DefaultTextChunkLocationComparator(!rightToLeftRunDirection)));

        textChunks.clear();

        for (TextChunk current : toSort) {
            TextChunkMarks currentMarks = marks.get(current);
            if (currentMarks != null) {
                if (!rightToLeftRunDirection) {
                    for (int j = 0; j < currentMarks.preceding.size(); j++) {
                        textChunks.add(currentMarks.preceding.get(j));
                    }
                } else {
                    for (int j = currentMarks.succeeding.size() - 1; j >= 0; j--) {
                        textChunks.add(currentMarks.succeeding.get(j));
                    }
                }
            }
            textChunks.add(current);
            if (currentMarks != null) {
                if (!rightToLeftRunDirection) {
                    for (int j = 0; j < currentMarks.succeeding.size(); j++) {
                        textChunks.add(currentMarks.succeeding.get(j));
                    }
                } else {
                    for (int j = currentMarks.preceding.size() - 1; j >= 0; j--) {
                        textChunks.add(currentMarks.preceding.get(j));
                    }
                }
            }
        }
    }

    public interface ITextChunkLocationStrategy {
        ITextChunkLocation createLocation(TextRenderInfo renderInfo, LineSegment baseline);
    }

    private static class TextChunkMarks {
        List<TextChunk> preceding = new ArrayList<>();
        List<TextChunk> succeeding = new ArrayList<>();
    }

}

⏎ com/itextpdf/kernel/pdf/canvas/parser/listener/LocationTextExtractionStrategy.java

Or download all of them as a single archive file:

File name: kernel-7.1.4-sources.jar
File size: 1201221 bytes
Release date: 2018-10-09
Download 

⇒ iText io.jar Source Code

⇐ Download and Install iText7-Core-7.1.4.zip

⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation