org.apache.log4j.NDC 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.util.Stack;
/**
* This class does not use generics to provide better source compatibility.
*/
public final class NDC {
private NDC() {
}
/**
* Clear any nested diagnostic information if any. This method is
* useful in cases where the same thread can be potentially used
* over and over in different unrelated contexts.
*
* This method is equivalent to calling the {@link #setMaxDepth}
* method with a zero maxDepth argument.
*
*/
public static void clear() {
org.apache.logging.log4j.ThreadContext.clearStack();
}
/**
* Clone the diagnostic context for the current thread.
*
* Internally a diagnostic context is represented as a stack. A
* given thread can supply the stack (i.e. diagnostic context) to a
* child thread so that the child can inherit the parent thread's
* diagnostic context.
*
*
* The child thread uses the {@link #inherit inherit} method to
* inherit the parent's diagnostic context.
*
* @return Stack A clone of the current thread's diagnostic context, Stack of Strings.
*/
@SuppressWarnings("rawtypes")
public static Stack cloneStack() {
final Stack stack = new Stack<>();
for (final String element : org.apache.logging.log4j.ThreadContext.cloneStack().asList()) {
stack.push(element);
}
return stack;
}
/**
* Inherit the diagnostic context of another thread, a Stack of Strings.
*
* The parent thread can obtain a reference to its diagnostic
* context using the {@link #cloneStack} method. It should
* communicate this information to its child so that it may inherit
* the parent's diagnostic context.
*
*
* The parent's diagnostic context is cloned before being
* inherited. In other words, once inherited, the two diagnostic
* contexts can be managed independently.
*
*
* In java, a child thread cannot obtain a reference to its
* parent, unless it is directly handed the reference. Consequently,
* there is no client-transparent way of inheriting diagnostic
* contexts. Do you know any solution to this problem?
*
* @param stack The diagnostic context of the parent thread, a Stack of Strings.
*/
@SuppressWarnings({"rawtypes", "unchecked"})
public static void inherit(final Stack stack) {
org.apache.logging.log4j.ThreadContext.setStack(stack);
}
/**
* Never use this method directly.
*
* @return The string value of the specified key.
*/
public static String get() {
return org.apache.logging.log4j.ThreadContext.peek();
}
/**
* Get the current nesting depth of this diagnostic context.
* @return int The number of elements in the call stack.
* @see #setMaxDepth
*/
public static int getDepth() {
return org.apache.logging.log4j.ThreadContext.getDepth();
}
/**
* Clients should call this method before leaving a diagnostic
* context.
*
* The returned value is the value that was pushed last. If no
* context is available, then the empty string "" is returned.
*
* @return String The innermost diagnostic context.
*/
public static String pop() {
return org.apache.logging.log4j.ThreadContext.pop();
}
/**
* Looks at the last diagnostic context at the top of this NDC
* without removing it.
*
* The returned value is the value that was pushed last. If no
* context is available, then the empty string "" is returned.
*
* @return String The innermost diagnostic context.
*/
public static String peek() {
return org.apache.logging.log4j.ThreadContext.peek();
}
/**
* Push new diagnostic context information for the current thread.
*
* The contents of the message parameter is
* determined solely by the client.
*
* @param message The new diagnostic context information.
*/
public static void push(final String message) {
org.apache.logging.log4j.ThreadContext.push(message);
}
/**
* Remove the diagnostic context for this thread.
*
* Each thread that created a diagnostic context by calling
* {@link #push} should call this method before exiting. Otherwise,
* the memory used by the thread cannot be reclaimed by the
* VM.
*
*
* As this is such an important problem in heavy duty systems and
* because it is difficult to always guarantee that the remove
* method is called before exiting a thread, this method has been
* augmented to lazily remove references to dead threads. In
* practice, this means that you can be a little sloppy and
* occasionally forget to call {@code remove} before exiting a
* thread. However, you must call remove sometime. If
* you never call it, then your application is sure to run out of
* memory.
*
*/
public static void remove() {
org.apache.logging.log4j.ThreadContext.removeStack();
}
/**
* Set maximum depth of this diagnostic context. If the current
* depth is smaller or equal to maxDepth, then no
* action is taken.
*
* This method is a convenient alternative to multiple {@link
* #pop} calls. Moreover, it is often the case that at the end of
* complex call sequences, the depth of the NDC is
* unpredictable. The setMaxDepth method circumvents
* this problem.
*
*
* For example, the combination
*
*
* void foo() {
* int depth = NDC.getDepth();
*
* ... complex sequence of calls
*
* NDC.setMaxDepth(depth);
* }
*
*
* ensures that between the entry and exit of foo the depth of the
* diagnostic stack is conserved.
*
*
* @see #getDepth
* @param maxDepth The maximum depth of the stack.
*/
public static void setMaxDepth(final int maxDepth) {
org.apache.logging.log4j.ThreadContext.trim(maxDepth);
}
}