/*
* 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 <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><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>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 <code>o</code> parameter) as identified
with the <code>key</code> parameter into the current thread's
context map.
<p>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 <code>key</code> parameter.
<p>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 <code>key</code>
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
}
}
}
}
}