Apache Log4j Core Implementation provides the functional components of the logging system. Users are free to create their own plugins and include them in the logging configuration. Apache Log4j Core is a required module to use Apache Log4j.

Bytecode (Java 8) for Apache Log4j Core Implementation is provided in a separate JAR file like log4j-core-2.14.1.jar.

Source Code files for Apache Log4j API are provided in both binary packge like apache-log4j-2.14.1-bin.zip and source package like apache-log4j-2.14.1-src.zip. You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j Core Implementation 2.14.1 below.

⏎ org/apache/logging/log4j/core/impl/ThrowableProxyRenderer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.core.impl;

import org.apache.logging.log4j.core.pattern.TextRenderer;
import org.apache.logging.log4j.util.Strings;

import java.util.List;

/**
 * {@link ThrowableProxyRenderer} is an internal utility providing the code to render a {@link ThrowableProxy}
 * to a {@link StringBuilder}.
 */
class ThrowableProxyRenderer {

    private static final String TAB = "\t";
    private static final String CAUSED_BY_LABEL = "Caused by: ";
    private static final String SUPPRESSED_LABEL = "Suppressed: ";
    private static final String WRAPPED_BY_LABEL = "Wrapped by: ";

    private ThrowableProxyRenderer() {
        // Utility Class
    }

    @SuppressWarnings("ThrowableResultOfMethodCallIgnored")
    static void formatWrapper(final StringBuilder sb, final ThrowableProxy cause, final List<String> ignorePackages,
                              final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        final Throwable caused = cause.getCauseProxy() != null ? cause.getCauseProxy().getThrowable() : null;
        if (caused != null) {
            formatWrapper(sb, cause.getCauseProxy(), ignorePackages, textRenderer, suffix, lineSeparator);
            sb.append(WRAPPED_BY_LABEL);
            renderSuffix(suffix, sb, textRenderer);
        }
        renderOn(cause, sb, textRenderer);
        renderSuffix(suffix, sb, textRenderer);
        textRenderer.render(lineSeparator, sb, "Text");
        formatElements(sb, Strings.EMPTY, cause.getCommonElementCount(),
                cause.getThrowable().getStackTrace(), cause.getExtendedStackTrace(), ignorePackages, textRenderer, suffix, lineSeparator);
    }

    private static void formatCause(final StringBuilder sb, final String prefix, final ThrowableProxy cause,
                                    final List<String> ignorePackages, final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        formatThrowableProxy(sb, prefix, CAUSED_BY_LABEL, cause, ignorePackages, textRenderer, suffix, lineSeparator);
    }

    private static void formatThrowableProxy(final StringBuilder sb, final String prefix, final String causeLabel,
                                             final ThrowableProxy throwableProxy, final List<String> ignorePackages,
                                             final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        if (throwableProxy == null) {
            return;
        }
        textRenderer.render(prefix, sb, "Prefix");
        textRenderer.render(causeLabel, sb, "CauseLabel");
        renderOn(throwableProxy, sb, textRenderer);
        renderSuffix(suffix, sb, textRenderer);
        textRenderer.render(lineSeparator, sb, "Text");
        formatElements(sb, prefix, throwableProxy.getCommonElementCount(),
                throwableProxy.getStackTrace(), throwableProxy.getExtendedStackTrace(), ignorePackages, textRenderer, suffix, lineSeparator);
        formatSuppressed(sb, prefix + TAB, throwableProxy.getSuppressedProxies(), ignorePackages, textRenderer, suffix, lineSeparator);
        formatCause(sb, prefix, throwableProxy.getCauseProxy(), ignorePackages, textRenderer, suffix, lineSeparator);
    }

    private static void formatSuppressed(final StringBuilder sb, final String prefix, final ThrowableProxy[] suppressedProxies,
                                         final List<String> ignorePackages, final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        if (suppressedProxies == null) {
            return;
        }
        for (final ThrowableProxy suppressedProxy : suppressedProxies) {
            formatThrowableProxy(sb, prefix, SUPPRESSED_LABEL, suppressedProxy, ignorePackages, textRenderer, suffix, lineSeparator);
        }
    }

    private static void formatElements(final StringBuilder sb, final String prefix, final int commonCount,
                                       final StackTraceElement[] causedTrace, final ExtendedStackTraceElement[] extStackTrace,
                                       final List<String> ignorePackages, final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        if (ignorePackages == null || ignorePackages.isEmpty()) {
            for (final ExtendedStackTraceElement element : extStackTrace) {
                formatEntry(element, sb, prefix, textRenderer, suffix, lineSeparator);
            }
        } else {
            int count = 0;
            for (int i = 0; i < extStackTrace.length; ++i) {
                if (!ignoreElement(causedTrace[i], ignorePackages)) {
                    if (count > 0) {
                        appendSuppressedCount(sb, prefix, count, textRenderer, suffix, lineSeparator);
                        count = 0;
                    }
                    formatEntry(extStackTrace[i], sb, prefix, textRenderer, suffix, lineSeparator);
                } else {
                    ++count;
                }
            }
            if (count > 0) {
                appendSuppressedCount(sb, prefix, count, textRenderer, suffix, lineSeparator);
            }
        }
        if (commonCount != 0) {
            textRenderer.render(prefix, sb, "Prefix");
            textRenderer.render("\t... ", sb, "More");
            textRenderer.render(Integer.toString(commonCount), sb, "More");
            textRenderer.render(" more", sb, "More");
            renderSuffix(suffix, sb, textRenderer);
            textRenderer.render(lineSeparator, sb, "Text");
        }
    }

    private static void renderSuffix(final String suffix, final StringBuilder sb, final TextRenderer textRenderer) {
        if (!suffix.isEmpty()) {
            textRenderer.render(" ", sb, "Suffix");
            textRenderer.render(suffix, sb, "Suffix");
        }
    }

    private static void appendSuppressedCount(final StringBuilder sb, final String prefix, final int count,
                                              final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        textRenderer.render(prefix, sb, "Prefix");
        if (count == 1) {
            textRenderer.render("\t... ", sb, "Suppressed");
        } else {
            textRenderer.render("\t... suppressed ", sb, "Suppressed");
            textRenderer.render(Integer.toString(count), sb, "Suppressed");
            textRenderer.render(" lines", sb, "Suppressed");
        }
        renderSuffix(suffix, sb, textRenderer);
        textRenderer.render(lineSeparator, sb, "Text");
    }

    private static void formatEntry(final ExtendedStackTraceElement extStackTraceElement, final StringBuilder sb,
                                    final String prefix, final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        textRenderer.render(prefix, sb, "Prefix");
        textRenderer.render("\tat ", sb, "At");
        extStackTraceElement.renderOn(sb, textRenderer);
        renderSuffix(suffix, sb, textRenderer);
        textRenderer.render(lineSeparator, sb, "Text");
    }

    private static boolean ignoreElement(final StackTraceElement element, final List<String> ignorePackages) {
        if (ignorePackages != null) {
            final String className = element.getClassName();
            for (final String pkg : ignorePackages) {
                if (className.startsWith(pkg)) {
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Formats the stack trace including packaging information.
     *
     * @param src            ThrowableProxy instance to format
     * @param sb             Destination.
     * @param ignorePackages List of packages to be ignored in the trace.
     * @param textRenderer   The message renderer.
     * @param suffix         Append this to the end of each stack frame.
     * @param lineSeparator  The end-of-line separator.
     */
    static void formatExtendedStackTraceTo(final ThrowableProxy src, final StringBuilder sb, final List<String> ignorePackages, final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        textRenderer.render(src.getName(), sb, "Name");
        textRenderer.render(": ", sb, "NameMessageSeparator");
        textRenderer.render(src.getMessage(), sb, "Message");
        renderSuffix(suffix, sb, textRenderer);
        textRenderer.render(lineSeparator, sb, "Text");
        final StackTraceElement[] causedTrace = src.getThrowable() != null ? src.getThrowable().getStackTrace() : null;
        formatElements(sb, Strings.EMPTY, 0, causedTrace, src.getExtendedStackTrace(), ignorePackages, textRenderer, suffix, lineSeparator);
        formatSuppressed(sb, TAB, src.getSuppressedProxies(), ignorePackages, textRenderer, suffix, lineSeparator);
        formatCause(sb, Strings.EMPTY, src.getCauseProxy(), ignorePackages, textRenderer, suffix, lineSeparator);
    }

    /**
     * Formats the Throwable that is the cause of the <pre>src</pre> Throwable.
     *
     * @param src            Throwable whose cause to render
     * @param sb             Destination to render the formatted Throwable that caused this Throwable onto.
     * @param ignorePackages The List of packages to be suppressed from the stack trace.
     * @param textRenderer   The text renderer.
     * @param suffix         Append this to the end of each stack frame.
     * @param lineSeparator  The end-of-line separator.
     */
    static void formatCauseStackTrace(final ThrowableProxy src, final StringBuilder sb, final List<String> ignorePackages, final TextRenderer textRenderer, final String suffix, final String lineSeparator) {
        final ThrowableProxy causeProxy = src.getCauseProxy();
        if (causeProxy != null) {
            formatWrapper(sb, causeProxy, ignorePackages, textRenderer, suffix, lineSeparator);
            sb.append(WRAPPED_BY_LABEL);
            ThrowableProxyRenderer.renderSuffix(suffix, sb, textRenderer);
        }
        renderOn(src, sb, textRenderer);
        ThrowableProxyRenderer.renderSuffix(suffix, sb, textRenderer);
        textRenderer.render(lineSeparator, sb, "Text");
        ThrowableProxyRenderer.formatElements(sb, Strings.EMPTY, 0, src.getStackTrace(), src.getExtendedStackTrace(),
                ignorePackages, textRenderer, suffix, lineSeparator);
    }

    private static void renderOn(final ThrowableProxy src, final StringBuilder output, final TextRenderer textRenderer) {
        final String msg = src.getMessage();
        textRenderer.render(src.getName(), output, "Name");
        if (msg != null) {
            textRenderer.render(": ", output, "NameMessageSeparator");
            textRenderer.render(msg, output, "Message");
        }
    }
}

⏎ org/apache/logging/log4j/core/impl/ThrowableProxyRenderer.java

 

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