/* * 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 mapped * diagnostic contexts. A Mapped Diagnostic Context, 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. *
*The MDC is managed on a per thread basis. A * child thread automatically inherits a copy of the mapped * diagnostic context of its parent. *
*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.
* *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:
* ** try { * MDC.put(myKey); * chain.doFilter(request, response); * } finally { * MDC.remove(myKey); * } ** *
Please also see: {@link http://logging.apache.org/log4j/1.2/faq.html#mdcmemoryleak}
* * @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 (theo
parameter) as identified
* with the key
parameter into the current thread's
* context map.
*
* 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 key
parameter.
*
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 key
* 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
}
}
}
}
}