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Java example source code file (MDC.java)

This example Java source code file (MDC.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

defaulting, failed, illegalargumentexception, illegalstateexception, map, mdcadapter, mdccloseable, no_static_mdc_binder_url, noclassdeffounderror, nosuchmethoderror, null_mdca_url, see, staticmdcbinder, string, util

The MDC.java Java example source code

/**
 * Copyright (c) 2004-2011 QOS.ch
 * All rights reserved.
 *
 * Permission is hereby granted, free  of charge, to any person obtaining
 * a  copy  of this  software  and  associated  documentation files  (the
 * "Software"), to  deal in  the Software without  restriction, including
 * without limitation  the rights to  use, copy, modify,  merge, publish,
 * distribute,  sublicense, and/or sell  copies of  the Software,  and to
 * permit persons to whom the Software  is furnished to do so, subject to
 * the following conditions:
 *
 * The  above  copyright  notice  and  this permission  notice  shall  be
 * included in all copies or substantial portions of the Software.
 *
 * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
 * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
 * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */
package org.slf4j;

import java.io.Closeable;
import java.util.Map;

import org.slf4j.helpers.NOPMDCAdapter;
import org.slf4j.helpers.BasicMDCAdapter;
import org.slf4j.helpers.Util;
import org.slf4j.impl.StaticMDCBinder;
import org.slf4j.spi.MDCAdapter;

/**
 * This class hides and serves as a substitute for the underlying logging
 * system's MDC implementation.
 * 
 * <p>
 * If the underlying logging system offers MDC functionality, then SLF4J's MDC,
 * i.e. this class, will delegate to the underlying system's MDC. Note that at
 * this time, only two logging systems, namely log4j and logback, offer MDC
 * functionality. For java.util.logging which does not support MDC,
 * {@link BasicMDCAdapter} will be used. For other systems, i.e slf4j-simple
 * and slf4j-nop, {@link NOPMDCAdapter} will be used.
 *
 * <p>
 * Thus, as a SLF4J user, you can take advantage of MDC in the presence of log4j,
 * logback, or java.util.logging, but without forcing these systems as
 * dependencies upon your users.
 * 
 * <p>
 * For more information on MDC please see the <a
 * href="http://logback.qos.ch/manual/mdc.html">chapter on MDC</a> in the
 * logback manual.
 * 
 * <p>
 * Please note that all methods in this class are static.
 * 
 * @author Ceki Gülcü
 * @since 1.4.1
 */
public class MDC {

    static final String NULL_MDCA_URL = "http://www.slf4j.org/codes.html#null_MDCA";
    static final String NO_STATIC_MDC_BINDER_URL = "http://www.slf4j.org/codes.html#no_static_mdc_binder";
    static MDCAdapter mdcAdapter;

    /**
     * An adapter to remove the key when done.
     */
    public static class MDCCloseable implements Closeable {
        private final String key;

        private MDCCloseable(String key) {
            this.key = key;
        }

        public void close() {
            MDC.remove(this.key);
        }
    }

    private MDC() {
    }

    /**
     * As of SLF4J version 1.7.14, StaticMDCBinder classes shipping in various bindings
     * come with a getSingleton() method. Previously only a public field called SINGLETON 
     * was available.
     * 
     * @return MDCAdapter
     * @throws NoClassDefFoundError in case no binding is available
     * @since 1.7.14
     */
    private static MDCAdapter bwCompatibleGetMDCAdapterFromBinder() throws NoClassDefFoundError {
        try {
            return StaticMDCBinder.getSingleton().getMDCA();
        } catch (NoSuchMethodError nsme) {
            // binding is probably a version of SLF4J older than 1.7.14
            return StaticMDCBinder.SINGLETON.getMDCA();
        }
    }

    static {
        try {
            mdcAdapter = bwCompatibleGetMDCAdapterFromBinder();
        } catch (NoClassDefFoundError ncde) {
            mdcAdapter = new NOPMDCAdapter();
            String msg = ncde.getMessage();
            if (msg != null && msg.contains("StaticMDCBinder")) {
                Util.report("Failed to load class \"org.slf4j.impl.StaticMDCBinder\".");
                Util.report("Defaulting to no-operation MDCAdapter implementation.");
                Util.report("See " + NO_STATIC_MDC_BINDER_URL + " for further details.");
            } else {
                throw ncde;
            }
        } catch (Exception e) {
            // we should never get here
            Util.report("MDC binding unsuccessful.", e);
        }
    }

    /**
     * Put a diagnostic context value (the <code>val parameter) as identified with the
     * <code>key parameter into the current thread's diagnostic context map. The
     * <code>key parameter cannot be null. The val parameter
     * can be null only if the underlying implementation supports it.
     * 
     * <p>
     * This method delegates all work to the MDC of the underlying logging system.
     *
     * @param key non-null key 
     * @param val value to put in the map
     * 
     * @throws IllegalArgumentException
     *           in case the "key" parameter is null
     */
    public static void put(String key, String val) throws IllegalArgumentException {
        if (key == null) {
            throw new IllegalArgumentException("key parameter cannot be null");
        }
        if (mdcAdapter == null) {
            throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
        }
        mdcAdapter.put(key, val);
    }

    /**
     * Put a diagnostic context value (the <code>val parameter) as identified with the
     * <code>key parameter into the current thread's diagnostic context map. The
     * <code>key parameter cannot be null. The val parameter
     * can be null only if the underlying implementation supports it.
     *
     * <p>
     * This method delegates all work to the MDC of the underlying logging system.
     * <p>
     * This method return a <code>Closeable object who can remove key when
     * <code>close is called.
     *
     * <p>
     * Useful with Java 7 for example :
     * <code>
     *   try(MDC.MDCCloseable closeable = MDC.putCloseable(key, value)) {
     *     ....
     *   }
     * </code>
     *
     * @param key non-null key
     * @param val value to put in the map
     * @return a <code>Closeable who can remove key when close
     * is called.
     *
     * @throws IllegalArgumentException
     *           in case the "key" parameter is null
     */
    public static MDCCloseable putCloseable(String key, String val) throws IllegalArgumentException {
        put(key, val);
        return new MDCCloseable(key);
    }

    /**
     * Get the diagnostic context identified by the <code>key parameter. The
     * <code>key parameter cannot be null.
     * 
     * <p>
     * This method delegates all work to the MDC of the underlying logging system.
     *
     * @param key  
     * @return the string value identified by the <code>key parameter.
     * @throws IllegalArgumentException
     *           in case the "key" parameter is null
     */
    public static String get(String key) throws IllegalArgumentException {
        if (key == null) {
            throw new IllegalArgumentException("key parameter cannot be null");
        }

        if (mdcAdapter == null) {
            throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
        }
        return mdcAdapter.get(key);
    }

    /**
     * Remove the diagnostic context identified by the <code>key parameter using
     * the underlying system's MDC implementation. The <code>key parameter
     * cannot be null. This method does nothing if there is no previous value
     * associated with <code>key.
     *
     * @param key  
     * @throws IllegalArgumentException
     *           in case the "key" parameter is null
     */
    public static void remove(String key) throws IllegalArgumentException {
        if (key == null) {
            throw new IllegalArgumentException("key parameter cannot be null");
        }

        if (mdcAdapter == null) {
            throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
        }
        mdcAdapter.remove(key);
    }

    /**
     * Clear all entries in the MDC of the underlying implementation.
     */
    public static void clear() {
        if (mdcAdapter == null) {
            throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
        }
        mdcAdapter.clear();
    }

    /**
     * Return a copy of the current thread's context map, with keys and values of
     * type String. Returned value may be null.
     * 
     * @return A copy of the current thread's context map. May be null.
     * @since 1.5.1
     */
    public static Map<String, String> getCopyOfContextMap() {
        if (mdcAdapter == null) {
            throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
        }
        return mdcAdapter.getCopyOfContextMap();
    }

    /**
     * Set the current thread's context map by first clearing any existing map and
     * then copying the map passed as parameter. The context map passed as
     * parameter must only contain keys and values of type String.
     * 
     * @param contextMap
     *          must contain only keys and values of type String
     * @since 1.5.1
     */
    public static void setContextMap(Map<String, String> contextMap) {
        if (mdcAdapter == null) {
            throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
        }
        mdcAdapter.setContextMap(contextMap);
    }

    /**
     * Returns the MDCAdapter instance currently in use.
     * 
     * @return the MDcAdapter instance currently in use.
     * @since 1.4.2
     */
    public static MDCAdapter getMDCAdapter() {
        return mdcAdapter;
    }

}

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