org.apache.log4j.MDC Maven / Gradle / Ivy
/*
* 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 java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Hashtable;
import org.apache.log4j.helpers.Loader;
import org.apache.log4j.helpers.ThreadLocalMap;
/**
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.
@since 1.2
@author Ceki Gülcü
*/
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 o 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.
*/
static
public
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.
*/
static
public
Object get(String key) {
if (mdc != null) {
return mdc.get0(key);
}
return null;
}
/**
Remove the the context identified by the key
parameter.
*/
static
public
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
}
}
}
}
}