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package org.wings.util;
import org.wings.session.SessionManager;
/**
* A helper class for storing session local variables similar to {@link ThreadLocal} for thread local variables.
*/
public class SessionLocal {
private final String propertyName;
public SessionLocal() {
this.propertyName = getClass().getName() + '.' + System.identityHashCode(this);
}
/**
* use a wrapper for the value so that it is possible
* to get and set a null value, and also to determine
* whether the property has been initialized
* for the current session
*/
private static class ValueWrapper {
T value;
}
/**
* return the current value of this variable from the session
*
* @return The current value or the result of {@link #initialValue()} if called for the first time.
*/
public T get() {
ValueWrapper valueWrapper = (ValueWrapper) SessionManager.getSession().getProperty(this.propertyName);
/*
* null means that the property is being used for the first time this session,
* initialize the value, which may be null.
*/
if (valueWrapper == null) {
T value = initialValue();
set(value);
return value;
}
else {
return valueWrapper.value;
}
}
/**
* override this method to get the initial value for a new session
*
* @return The stored value
*/
protected T initialValue() {
return null;
}
/**
* Set the value. the value which is set may be null,
* but the object set is never null because it is wrapped.
*
* @param value Value. null is also a valid value.
*/
public void set(T value) {
ValueWrapper valueWrapper = new ValueWrapper<>();
valueWrapper.value = value;
SessionManager.getSession().setProperty(this.propertyName, valueWrapper);
}
/**
* remove the value,
* if get is called, the value will be reinitialized
*/
public void remove() {
SessionManager.getSession().setProperty(this.propertyName, null);
}
}