org.apache.logging.log4j.ThreadContext 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.logging.log4j;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import org.apache.logging.log4j.message.ParameterizedMessage;
import org.apache.logging.log4j.spi.DefaultThreadContextMap;
import org.apache.logging.log4j.spi.DefaultThreadContextStack;
import org.apache.logging.log4j.spi.NoOpThreadContextMap;
import org.apache.logging.log4j.spi.ReadOnlyThreadContextMap;
import org.apache.logging.log4j.spi.ThreadContextMap;
import org.apache.logging.log4j.spi.ThreadContextMap2;
import org.apache.logging.log4j.spi.CleanableThreadContextMap;
import org.apache.logging.log4j.spi.ThreadContextMapFactory;
import org.apache.logging.log4j.spi.ThreadContextStack;
import org.apache.logging.log4j.util.PropertiesUtil;
/**
* The ThreadContext allows applications to store information either in a Map or a Stack.
*
* The MDC is managed on a per thread basis. To enable automatic inheritance of copies of the MDC
* to newly created threads, enable the {@value DefaultThreadContextMap#INHERITABLE_MAP} Log4j system property.
*
* @see Thread Context Manual
*/
public final class ThreadContext {
/**
* An empty read-only ThreadContextStack.
*/
private static class EmptyThreadContextStack extends AbstractCollection implements ThreadContextStack {
private static final long serialVersionUID = 1L;
private static final Iterator EMPTY_ITERATOR = new EmptyIterator<>();
@Override
public String pop() {
return null;
}
@Override
public String peek() {
return null;
}
@Override
public void push(final String message) {
throw new UnsupportedOperationException();
}
@Override
public int getDepth() {
return 0;
}
@Override
public List asList() {
return Collections.emptyList();
}
@Override
public void trim(final int depth) {
// Do nothing
}
@Override
public boolean equals(final Object o) {
// Similar to java.util.Collections.EmptyList.equals(Object)
return (o instanceof Collection) && ((Collection) o).isEmpty();
}
@Override
public int hashCode() {
// Same as java.util.Collections.EmptyList.hashCode()
return 1;
}
@Override
public ContextStack copy() {
return this;
}
@Override
public T[] toArray(final T[] a) {
throw new UnsupportedOperationException();
}
@Override
public boolean add(final String e) {
throw new UnsupportedOperationException();
}
@Override
public boolean containsAll(final Collection c) {
return false;
}
@Override
public boolean addAll(final Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean removeAll(final Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean retainAll(final Collection c) {
throw new UnsupportedOperationException();
}
@Override
public Iterator iterator() {
return EMPTY_ITERATOR;
}
@Override
public int size() {
return 0;
}
@Override
public ContextStack getImmutableStackOrNull() {
return this;
}
}
/**
* An empty iterator. Since Java 1.7 added the Collections.emptyIterator() method, we have to make do.
*
* @param the type of the empty iterator
*/
private static class EmptyIterator implements Iterator {
@Override
public boolean hasNext() {
return false;
}
@Override
public E next() {
throw new NoSuchElementException("This is an empty iterator!");
}
@Override
public void remove() {
// no-op
}
}
/**
* Empty, immutable Map.
*/
// ironically, this annotation gives an "unsupported @SuppressWarnings" warning in Eclipse
@SuppressWarnings("PublicStaticCollectionField")
// I like irony, so I won't delete it...
public static final Map EMPTY_MAP = Collections.emptyMap();
/**
* Empty, immutable ContextStack.
*/
// ironically, this annotation gives an "unsupported @SuppressWarnings" warning in Eclipse
@SuppressWarnings("PublicStaticCollectionField")
public static final ThreadContextStack EMPTY_STACK = new EmptyThreadContextStack();
private static final String DISABLE_MAP = "disableThreadContextMap";
private static final String DISABLE_STACK = "disableThreadContextStack";
private static final String DISABLE_ALL = "disableThreadContext";
private static boolean disableAll;
private static boolean useMap;
private static boolean useStack;
private static ThreadContextMap contextMap;
private static ThreadContextStack contextStack;
private static ReadOnlyThreadContextMap readOnlyContextMap;
static {
init();
}
private ThreadContext() {
// empty
}
/**
* Consider private, used for testing.
*/
static void init() {
ThreadContextMapFactory.init();
contextMap = null;
final PropertiesUtil managerProps = PropertiesUtil.getProperties();
disableAll = managerProps.getBooleanProperty(DISABLE_ALL);
useStack = !(managerProps.getBooleanProperty(DISABLE_STACK) || disableAll);
useMap = !(managerProps.getBooleanProperty(DISABLE_MAP) || disableAll);
contextStack = new DefaultThreadContextStack(useStack);
if (!useMap) {
contextMap = new NoOpThreadContextMap();
} else {
contextMap = ThreadContextMapFactory.createThreadContextMap();
}
if (contextMap instanceof ReadOnlyThreadContextMap) {
readOnlyContextMap = (ReadOnlyThreadContextMap) contextMap;
} else {
readOnlyContextMap = null;
}
}
/**
* Puts a context value (the value 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.
*
*
* @param key The key name.
* @param value The key value.
*/
public static void put(final String key, final String value) {
contextMap.put(key, value);
}
/**
* Puts all given context map entries into the current thread's
* context map.
*
* If the current thread does not have a context map it is
* created as a side effect.
* @param m The map.
* @since 2.7
*/
public static void putAll(final Map m) {
if (contextMap instanceof ThreadContextMap2) {
((ThreadContextMap2) contextMap).putAll(m);
} else if (contextMap instanceof DefaultThreadContextMap) {
((DefaultThreadContextMap) contextMap).putAll(m);
} else {
for (final Map.Entry entry: m.entrySet()) {
contextMap.put(entry.getKey(), entry.getValue());
}
}
}
/**
* Gets the context value identified by the key parameter.
*
*
* This method has no side effects.
*
*
* @param key The key to locate.
* @return The value associated with the key or null.
*/
public static String get(final String key) {
return contextMap.get(key);
}
/**
* Removes the context value identified by the key parameter.
*
* @param key The key to remove.
*/
public static void remove(final String key) {
contextMap.remove(key);
}
/**
* Removes the context values identified by the keys parameter.
*
* @param keys The keys to remove.
*
* @since 2.8
*/
public static void removeAll(final Iterable keys) {
if (contextMap instanceof CleanableThreadContextMap) {
((CleanableThreadContextMap) contextMap).removeAll(keys);
} else if (contextMap instanceof DefaultThreadContextMap) {
((DefaultThreadContextMap) contextMap).removeAll(keys);
} else {
for (final String key : keys) {
contextMap.remove(key);
}
}
}
/**
* Clears the context map.
*/
public static void clearMap() {
contextMap.clear();
}
/**
* Clears the context map and stack.
*/
public static void clearAll() {
clearMap();
clearStack();
}
/**
* Determines if the key is in the context.
*
* @param key The key to locate.
* @return True if the key is in the context, false otherwise.
*/
public static boolean containsKey(final String key) {
return contextMap.containsKey(key);
}
/**
* Returns a mutable copy of current thread's context Map.
*
* @return a mutable copy of the context.
*/
public static Map getContext() {
return contextMap.getCopy();
}
/**
* Returns an immutable view of the current thread's context Map.
*
* @return An immutable view of the ThreadContext Map.
*/
public static Map getImmutableContext() {
final Map map = contextMap.getImmutableMapOrNull();
return map == null ? EMPTY_MAP : map;
}
/**
* Returns a read-only view of the internal data structure used to store thread context key-value pairs,
* or {@code null} if the internal data structure does not implement the
* {@code ReadOnlyThreadContextMap} interface.
*
* The {@link DefaultThreadContextMap} implementation does not implement {@code ReadOnlyThreadContextMap}, so by
* default this method returns {@code null}.
*
*
* @return the internal data structure used to store thread context key-value pairs or {@code null}
* @see ThreadContextMapFactory
* @see DefaultThreadContextMap
* @see org.apache.logging.log4j.spi.CopyOnWriteSortedArrayThreadContextMap
* @see org.apache.logging.log4j.spi.GarbageFreeSortedArrayThreadContextMap
* @since 2.8
*/
public static ReadOnlyThreadContextMap getThreadContextMap() {
return readOnlyContextMap;
}
/**
* Returns true if the Map is empty.
*
* @return true if the Map is empty, false otherwise.
*/
public static boolean isEmpty() {
return contextMap.isEmpty();
}
/**
* Clears the stack for this thread.
*/
public static void clearStack() {
contextStack.clear();
}
/**
* Returns a copy of this thread's stack.
*
* @return A copy of this thread's stack.
*/
public static ContextStack cloneStack() {
return contextStack.copy();
}
/**
* Gets an immutable copy of this current thread's context stack.
*
* @return an immutable copy of the ThreadContext stack.
*/
public static ContextStack getImmutableStack() {
final ContextStack result = contextStack.getImmutableStackOrNull();
return result == null ? EMPTY_STACK : result;
}
/**
* Sets this thread's stack.
*
* @param stack The stack to use.
*/
public static void setStack(final Collection stack) {
if (stack.isEmpty() || !useStack) {
return;
}
contextStack.clear();
contextStack.addAll(stack);
}
/**
* Gets the current nesting depth of this thread's stack.
*
* @return the number of items in the stack.
*
* @see #trim
*/
public static int getDepth() {
return contextStack.getDepth();
}
/**
* Returns the value of the last item placed on the stack.
*
*
* 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 contextStack.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 contextStack.peek();
}
/**
* Pushes 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) {
contextStack.push(message);
}
/**
* Pushes new diagnostic context information for the current thread.
*
*
* The contents of the message and args parameters are determined solely by the client. The message
* will be treated as a format String and tokens will be replaced with the String value of the arguments in
* accordance with ParameterizedMessage.
*
*
* @param message The new diagnostic context information.
* @param args Parameters for the message.
*/
public static void push(final String message, final Object... args) {
contextStack.push(ParameterizedMessage.format(message, args));
}
/**
* Removes 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
* {@link #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 removeStack() {
contextStack.clear();
}
/**
* Trims elements from this diagnostic context. If the current depth is smaller or equal to maxDepth,
* then no action is taken. If the current depth is larger than newDepth then all elements at maxDepth or higher are
* discarded.
*
*
* 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 ThreadContext is unpredictable. The trim method
* circumvents this problem.
*
*
*
* For example, the combination
*
*
*
* void foo() {
* final int depth = ThreadContext.getDepth();
*
* // ... complex sequence of calls
*
* ThreadContext.trim(depth);
* }
*
*
*
* ensures that between the entry and exit of {@code foo} the depth of the diagnostic stack is conserved.
*
*
* @see #getDepth
* @param depth The number of elements to keep.
*/
public static void trim(final int depth) {
contextStack.trim(depth);
}
/**
* The ThreadContext Stack interface.
*/
public interface ContextStack extends Serializable, Collection {
/**
* Returns the element at the top of the stack.
*
* @return The element at the top of the stack.
* @throws java.util.NoSuchElementException if the stack is empty.
*/
String pop();
/**
* Returns the element at the top of the stack without removing it or null if the stack is empty.
*
* @return the element at the top of the stack or null if the stack is empty.
*/
String peek();
/**
* Pushes an element onto the stack.
*
* @param message The element to add.
*/
void push(String message);
/**
* Returns the number of elements in the stack.
*
* @return the number of elements in the stack.
*/
int getDepth();
/**
* Returns all the elements in the stack in a List.
*
* @return all the elements in the stack in a List.
*/
List asList();
/**
* Trims elements from the end of the stack.
*
* @param depth The maximum number of items in the stack to keep.
*/
void trim(int depth);
/**
* Returns a copy of the ContextStack.
*
* @return a copy of the ContextStack.
*/
ContextStack copy();
/**
* Returns a ContextStack with the same contents as this ContextStack or {@code null}. Attempts to modify the
* returned stack may or may not throw an exception, but will not affect the contents of this ContextStack.
*
* @return a ContextStack with the same contents as this ContextStack or {@code null}.
*/
ContextStack getImmutableStackOrNull();
}
}
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