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/counter/data/EventDataHandler.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.counter.data;

import com.itextpdf.io.util.SystemUtil;
import com.itextpdf.kernel.counter.event.IEvent;
import com.itextpdf.kernel.counter.event.IMetaInfo;

import java.util.Collections;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;

/**
 * This class is intended for some heavy concurrent event operations
 * (like writing to database or file).
 *
 * On registration of new {@link IEvent} the instance of {@link EventData} is created with
 * the {@link IEventDataFactory} that can add some additional information like system info
 * or version.
 * This data instance is immediately cached with {@link IEventDataCache} that can for example
 * merge data with the same signature by summing there count.
 * If the previous processing operation is finished and the wait time is passed then the next event is retrieved from cache
 * (it may be for example based on some comparator like the biggest count, if {@link EventDataCacheComparatorBased}
 * is used, or just queue based if the {@link EventDataCacheQueueBased} is used or any other order determined by
 * custom cache) and the processing is started asynchronously
 *
 * This class can be considered thread-safe if the cache and factory instances aren't used anywhere else in the code.
 *
 * @param <T> data signature type
 * @param <V> data type
 */
public abstract class EventDataHandler<T, V extends EventData<T>> {
    private final Object processLock = new Object();

    private final IEventDataCache<T, V> cache;
    private final IEventDataFactory<T, V> factory;
    private final AtomicLong lastProcessedTime = new AtomicLong();

    private volatile WaitTime waitTime;

    public EventDataHandler(IEventDataCache<T, V> cache, IEventDataFactory<T, V> factory, long initialWaitTimeMillis, long maxWaitTimeMillis) {
        this.cache = cache;
        this.factory = factory;
        this.waitTime = new WaitTime(initialWaitTimeMillis, maxWaitTimeMillis);
    }

    public List<V> clear() {
        List<V> all;
        synchronized (cache) {
            all = cache.clear();
        }
        lastProcessedTime.set(0);
        resetWaitTime();
        return all != null ? all : Collections.<V>emptyList();
    }

    public void register(IEvent event, IMetaInfo metaInfo) {
        V data;
        //Synchronization is left here mostly in consistency with cache and process, but factories are usually not thread safe anyway.
        synchronized (factory) {
            data = factory.create(event, metaInfo);
        }
        if (data != null) {
            synchronized (cache) {
                cache.put(data);
            }
            tryProcessNextAsync();
        }
    }

    public void tryProcessNext() {
        long currentTime = SystemUtil.getRelativeTimeMillis();
        if (currentTime - lastProcessedTime.get() > waitTime.getTime()) {
            lastProcessedTime.set(SystemUtil.getRelativeTimeMillis());
            V data;
            synchronized (cache) {
                data = cache.retrieveNext();
            }
            if (data != null) {
                boolean successful;
                synchronized (processLock) {
                    successful = tryProcess(data);
                }
                if (successful) {
                    onSuccess(data);
                } else {
                    synchronized (cache) {
                        cache.put(data);
                    }
                    onFailure(data);
                }
            }
        }
    }

    public void tryProcessNextAsync() {
        tryProcessNextAsync(null);
    }

    public void tryProcessNextAsync(Boolean daemon) {
        long currentTime = SystemUtil.getRelativeTimeMillis();
        if (currentTime - lastProcessedTime.get() > waitTime.getTime()) {
            Thread thread = new Thread() {
                @Override
                public void run() {
                    tryProcessNext();
                }
            };
            if (daemon != null) {
                thread.setDaemon((boolean) daemon);
            }
            thread.start();
        }
    }

    /**
     * Method that will try to immediately process all cashed data, ignoring the usual error fallback procedures.
     */
    public void tryProcessRest() {
        List<V> unprocessedEvents = clear();
        if (!unprocessedEvents.isEmpty()) {
            try {
                synchronized (processLock) {
                    for (V data : unprocessedEvents) {
                        process(data);
                    }
                }
            } catch (Exception ignored) {
            }
        }
    }

    public void resetWaitTime() {
        WaitTime local = waitTime;
        waitTime = new WaitTime(local.getInitial(), local.getMaximum());
    }

    public void increaseWaitTime() {
        WaitTime local = waitTime;
        waitTime = new WaitTime(local.getInitial(), local.getMaximum(), Math.min(local.getTime() * 2, local.getMaximum()));
    }

    public void setNoWaitTime() {
        WaitTime local = waitTime;
        waitTime = new WaitTime(local.getInitial(), local.getMaximum(), 0);
    }

    public WaitTime getWaitTime() {
        return waitTime;
    }

    protected void onSuccess(V data) {
        resetWaitTime();
    }

    protected void onFailure(V data) {
        increaseWaitTime();
    }

    /**
     * Is called when exception is thrown in process.
     *
     * @param exception caught exception
     * @return whether processing is treated as success
     */
    protected boolean onProcessException(Exception exception) {
        return false;
    }

    protected abstract boolean process(V data);

    private boolean tryProcess(V data) {
        try {
            return process(data);
        } catch (Exception any) {
            return onProcessException(any);
        }
    }
}

⏎ com/itextpdf/kernel/counter/data/EventDataHandler.java

 

⇒ iText io.jar Source Code

⇐ Download and Install iText7-Core-7.1.4.zip

⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation