jodd.util.cl.ClassLoaderLocal Maven / Gradle / Ivy
// Copyright (c) 2003-present, Jodd Team (http://jodd.org)
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//
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package jodd.util.cl;
import java.util.Map;
import java.util.WeakHashMap;
/**
* This class provides classloader-local variables.
*
* It is designed to look very much like ThreadLocal.
*/
public class ClassLoaderLocal {
private final Map weakMap = new WeakHashMap<>();
private T value;
private boolean initialized;
/**
* Returns the current classloader "initial value" for this classloader-local variable.
* This method will be invoked the first time it is accessed the get() method, unless
* the thread previously invoked the set(T) method, in which case the initialValue method
* will not be invoked for the classloader. Normally, this method is invoked at most once
* per classloader, but it may be invoked again in case of subsequent invocations of remove()
* followed by get().
*
* This implementation simply returns null; if the programmer desires classloader-local variables to
* have an initial value other than null, ClassLoaderLocal must be subclassed, and this method overridden.
* Typically, an anonymous inner class will be used.
*/
protected T initialValue() {
return null;
}
/**
* Returns the value in the current classloader copy of this variable.
* If the variable has no value for the current classloader, it is first initialized to the value returned
* by an invocation of the initialValue() method.
*/
public synchronized T get() {
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null) {
T value = weakMap.get(contextClassLoader);
if ((value == null) && !weakMap.containsKey(contextClassLoader)) {
value = initialValue();
weakMap.put(contextClassLoader, value);
}
return value;
}
if (!initialized) {
value = initialValue();
initialized = true;
}
return value;
}
/**
* Sets the current classloaders's copy of this variable to the specified value.
* Most subclasses will have no need to override this method, relying solely on the initialValue()
* method to set the values of classloader-locals.
*/
public synchronized void set(final T value) {
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null) {
weakMap.put(contextClassLoader, value);
return;
}
this.value = value;
this.initialized = true;
}
/**
* Removes the current classloader's value for this variable.
*/
public synchronized void remove() {
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
weakMap.remove(contextClassLoader);
}
}