/*
* 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.log4j;
import org.apache.log4j.helpers.Loader;
import org.apache.log4j.helpers.ThreadLocalMap;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Hashtable;
/**
* The MDC class is similar to the {@link NDC} class except that it is
* based on a map instead of a stack. It provides <em>mapped
* diagnostic contexts</em>. A <em>Mapped Diagnostic Context</em>, or
* MDC in short, is an instrument for distinguishing interleaved log
* output from different sources. Log output is typically interleaved
* when a server handles multiple clients near-simultaneously.
* <p/>
* <p><b><em>The MDC is managed on a per thread basis</em></b>. A
* child thread automatically inherits a <em>copy</em> of the mapped
* diagnostic context of its parent.
* <p/>
* <p>The MDC class requires JDK 1.2 or above. Under JDK 1.1 the MDC
* will always return empty values but otherwise will not affect or
* harm your application.</p>
*
* <p>Attention: the application is required to clean up. In web applications
* this can happen with creating a Servlet Filter and overriding the
* onFilter method like:</p>
*
* <pre>
* try {
* MDC.put(myKey);
* chain.doFilter(request, response);
* } finally {
* MDC.remove(myKey);
* }
* </pre>
*
* <p>Please also see: {@link http://logging.apache.org/log4j/1.2/faq.html#mdcmemoryleak}</p>
*
* @author Ceki Gülcü
* @since 1.2
*/
public class MDC {
final static MDC mdc = new MDC();
static final int HT_SIZE = 7;
boolean java1;
Object tlm;
private Method removeMethod;
private MDC() {
java1 = Loader.isJava1();
if (!java1) {
tlm = new ThreadLocalMap();
}
try {
removeMethod = ThreadLocal.class.getMethod("remove", null);
} catch (NoSuchMethodException e) {
// don't do anything - java prior 1.5
}
}
/**
* Put a context value (the <code>o</code> parameter) as identified
* with the <code>key</code> parameter into the current thread's
* context map.
* <p/>
* <p>If the current thread does not have a context map it is
* created as a side effect.
*/
public static void put(String key, Object o) {
if (mdc != null) {
mdc.put0(key, o);
}
}
/**
* Get the context identified by the <code>key</code> parameter.
* <p/>
* <p>This method has no side effects.
*/
public static Object get(String key) {
if (mdc != null) {
return mdc.get0(key);
}
return null;
}
/**
* Remove the the context identified by the <code>key</code>
* parameter.
*/
public static void remove(String key) {
if (mdc != null) {
mdc.remove0(key);
}
}
/**
* Get the current thread's MDC as a hashtable. This method is
* intended to be used internally.
*/
public static Hashtable getContext() {
if (mdc != null) {
return mdc.getContext0();
} else {
return null;
}
}
/**
* Remove all values from the MDC.
*
* @since 1.2.16
*/
public static void clear() {
if (mdc != null) {
mdc.clear0();
}
}
private void put0(String key, Object o) {
if (java1 || tlm == null) {
return;
} else {
Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
if (ht == null) {
ht = new Hashtable(HT_SIZE);
((ThreadLocalMap) tlm).set(ht);
}
ht.put(key, o);
}
}
private Object get0(String key) {
if (java1 || tlm == null) {
return null;
} else {
Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
if (ht != null && key != null) {
return ht.get(key);
} else {
return null;
}
}
}
private void remove0(String key) {
if (!java1 && tlm != null) {
Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
if (ht != null) {
ht.remove(key);
// clean up if this was the last key
if (ht.isEmpty()) {
clear0();
}
}
}
}
private Hashtable getContext0() {
if (java1 || tlm == null) {
return null;
} else {
return (Hashtable) ((ThreadLocalMap) tlm).get();
}
}
private void clear0() {
if (!java1 && tlm != null) {
Hashtable ht = (Hashtable) ((ThreadLocalMap) tlm).get();
if (ht != null) {
ht.clear();
}
if (removeMethod != null) {
// java 1.3/1.4 does not have remove - will suffer from a memory leak
try {
removeMethod.invoke(tlm, null);
} catch (IllegalAccessException e) {
// should not happen
} catch (InvocationTargetException e) {
// should not happen
}
}
}
}
}