* * Most application services use a singleton object to provide their * services, either as a default (such as getSystemEventQueue or * getDefaultToolkit) or as static methods with class data (System). * The AppContext works with the former method by extending the concept * of "default" to be ThreadGroup-specific. Application services * lookup their singleton in the AppContext.
* * For example, here we have a Foo service, with its pre-AppContext * code:
*
* public class Foo {
* private static Foo defaultFoo = new Foo();
*
* public static Foo getDefaultFoo() {
* return defaultFoo;
* }
*
* ... Foo service methods
* }
* * The problem with the above is that the Foo service is global in scope, * so that applets and other untrusted code can execute methods on the * single, shared Foo instance. The Foo service therefore either needs * to block its use by untrusted code using a SecurityManager test, or * restrict its capabilities so that it doesn't matter if untrusted code * executes it.
* * Here's the Foo class written to use the AppContext:
*
* public class Foo {
* public static Foo getDefaultFoo() {
* Foo foo = (Foo)AppContext.getAppContext().get(Foo.class);
* if (foo == null) {
* foo = new Foo();
* getAppContext().put(Foo.class, foo);
* }
* return foo;
* }
*
* ... Foo service methods
* }
* * Since a separate AppContext can exist for each ThreadGroup, trusted * and untrusted code have access to different Foo instances. This allows * untrusted code access to "system-wide" services -- the service remains * within the AppContext "sandbox". For example, say a malicious applet * wants to peek all of the key events on the EventQueue to listen for * passwords; if separate EventQueues are used for each ThreadGroup * using AppContexts, the only key events that applet will be able to * listen to are its own. A more reasonable applet request would be to * change the Swing default look-and-feel; with that default stored in * an AppContext, the applet's look-and-feel will change without * disrupting other applets or potentially the browser itself.
*
* Because the AppContext is a facility for safely extending application
* service support to applets, none of its methods may be blocked by a
* a SecurityManager check in a valid Java implementation. Applets may
* therefore safely invoke any of its methods without worry of being
* blocked.
*
* Note: If a SecurityManager is installed which derives from
* sun.awt.AWTSecurityManager, it may override the
* AWTSecurityManager.getAppContext() method to return the proper
* AppContext based on the execution context, in the case where
* the default ThreadGroup-based AppContext indexing would return
* the main "system" AppContext. For example, in an applet situation,
* if a system thread calls into an applet, rather than returning the
* main "system" AppContext (the one corresponding to the system thread),
* an installed AWTSecurityManager may return the applet's AppContext
* based on the execution context.
*
* @author Thomas Ball
* @author Fred Ecks
*/
public final class AppContext {
private static final PlatformLogger log = PlatformLogger.getLogger("sun.awt.AppContext");
/* Since the contents of an AppContext are unique to each Java
* session, this class should never be serialized. */
/*
* The key to put()/get() the Java EventQueue into/from the AppContext.
*/
public static final Object EVENT_QUEUE_KEY = new StringBuffer("EventQueue");
/*
* The keys to store EventQueue push/pop lock and condition.
*/
public final static Object EVENT_QUEUE_LOCK_KEY = new StringBuilder("EventQueue.Lock");
public final static Object EVENT_QUEUE_COND_KEY = new StringBuilder("EventQueue.Condition");
/* A map of AppContexts, referenced by ThreadGroup.
*/
private static final Map
* The value can be retrieved by calling the
* If listener is null, no exception is thrown and no action is performed.
*
* @param propertyName one of the property names listed above
* @param listener the PropertyChangeListener to be added
*
* @see #removePropertyChangeListener(java.lang.String, java.beans.PropertyChangeListener)
* @see #getPropertyChangeListeners(java.lang.String)
* @see #addPropertyChangeListener(java.lang.String, java.beans.PropertyChangeListener)
*/
public synchronized void addPropertyChangeListener(
String propertyName,
PropertyChangeListener listener) {
if (listener == null) {
return;
}
if (changeSupport == null) {
changeSupport = new PropertyChangeSupport(this);
}
changeSupport.addPropertyChangeListener(propertyName, listener);
}
/**
* Removes a PropertyChangeListener from the listener list for a specific
* property. This method should be used to remove PropertyChangeListeners
* that were registered for a specific bound property.
*
* If listener is null, no exception is thrown and no action is performed.
*
* @param propertyName a valid property name
* @param listener the PropertyChangeListener to be removed
*
* @see #addPropertyChangeListener(java.lang.String, java.beans.PropertyChangeListener)
* @see #getPropertyChangeListeners(java.lang.String)
* @see #removePropertyChangeListener(java.beans.PropertyChangeListener)
*/
public synchronized void removePropertyChangeListener(
String propertyName,
PropertyChangeListener listener) {
if (listener == null || changeSupport == null) {
return;
}
changeSupport.removePropertyChangeListener(propertyName, listener);
}
/**
* Returns an array of all the listeners which have been associated
* with the named property.
*
* @return all of the AppContexts.
*/
public static SetPropertyChangeListeners have been registered,
* the changeSupport field describes them.
*
* @see #addPropertyChangeListener
* @see #removePropertyChangeListener
* @see #firePropertyChange
*/
private PropertyChangeSupport changeSupport = null;
public static final String DISPOSED_PROPERTY_NAME = "disposed";
public static final String GUI_DISPOSED = "guidisposed";
private volatile boolean isDisposed = false; // true if AppContext is disposed
public boolean isDisposed() {
return isDisposed;
}
/*
* The total number of AppContexts, system-wide. This number is
* incremented at the beginning of the constructor, and decremented
* at the end of dispose(). getAppContext() checks to see if this
* number is 1. If so, it returns the sole AppContext without
* checking Thread.currentThread().
*/
private static final AtomicInteger numAppContexts = new AtomicInteger(0);
static {
// On the main Thread, we get the ThreadGroup, make a corresponding
// AppContext, and instantiate the Java EventQueue. This way, legacy
// code is unaffected by the move to multiple AppContext ability.
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
ThreadGroup currentThreadGroup =
Thread.currentThread().getThreadGroup();
ThreadGroup parentThreadGroup = currentThreadGroup.getParent();
while (parentThreadGroup != null) {
// Find the root ThreadGroup to construct our main AppContext
currentThreadGroup = parentThreadGroup;
parentThreadGroup = currentThreadGroup.getParent();
}
mainAppContext = new AppContext(currentThreadGroup);
return mainAppContext;
}
});
}
/*
* The context ClassLoader that was used to create this AppContext.
*/
private final ClassLoader contextClassLoader;
/**
* Constructor for AppContext. This method is not public,
* nor should it ever be used as such. The proper way to construct
* an AppContext is through the use of SunToolkit.createNewAppContext.
* A ThreadGroup is created for the new AppContext, a Thread is
* created within that ThreadGroup, and that Thread calls
* SunToolkit.createNewAppContext before calling anything else.
* That creates both the new AppContext and its EventQueue.
*
* @param threadGroup The ThreadGroup for the new AppContext
* @see sun.awt.SunToolkit
* @since 1.2
*/
AppContext(ThreadGroup threadGroup) {
numAppContexts.incrementAndGet();
this.threadGroup = threadGroup;
threadGroup2appContext.put(threadGroup, this);
this.contextClassLoader =
AccessController.doPrivileged(new PrivilegedActionnull if the key is not mapped to any value.
* @see #put(Object, Object)
* @since 1.2
*/
public Object get(Object key) {
/*
* The most recent reference should be updated inside a synchronized
* block to avoid a race when put() and get() are executed in
* parallel on different threads.
*/
synchronized (table) {
// Note: this most recent key/value caching is thread-hot.
// A simple test using SwingSet found that 72% of lookups
// were matched using the most recent key/value. By instantiating
// a simple MostRecentKeyValue object on cache misses, the
// cache hits can be processed without synchronization.
MostRecentKeyValue recent = mostRecentKeyValue;
if ((recent != null) && (recent.key == key)) {
return recent.value;
}
Object value = table.get(key);
if(mostRecentKeyValue == null) {
mostRecentKeyValue = new MostRecentKeyValue(key, value);
shadowMostRecentKeyValue = new MostRecentKeyValue(key, value);
} else {
MostRecentKeyValue auxKeyValue = mostRecentKeyValue;
shadowMostRecentKeyValue.setPair(key, value);
mostRecentKeyValue = shadowMostRecentKeyValue;
shadowMostRecentKeyValue = auxKeyValue;
}
return value;
}
}
/**
* Maps the specified key to the specified
* value in this AppContext. Neither the key nor the
* value can be null.
* get method
* with a key that is equal to the original key.
*
* @param key the AppContext key.
* @param value the value.
* @return the previous value of the specified key in this
* AppContext, or null if it did not have one.
* @exception NullPointerException if the key or value is
* null.
* @see #get(Object)
* @since 1.2
*/
public Object put(Object key, Object value) {
synchronized (table) {
MostRecentKeyValue recent = mostRecentKeyValue;
if ((recent != null) && (recent.key == key))
recent.value = value;
return table.put(key, value);
}
}
/**
* Removes the key (and its corresponding value) from this
* AppContext. This method does nothing if the key is not in the
* AppContext.
*
* @param key the key that needs to be removed.
* @return the value to which the key had been mapped in this AppContext,
* or null if the key did not have a mapping.
* @since 1.2
*/
public Object remove(Object key) {
synchronized (table) {
MostRecentKeyValue recent = mostRecentKeyValue;
if ((recent != null) && (recent.key == key))
recent.value = null;
return table.remove(key);
}
}
/**
* Returns the root ThreadGroup for all Threads contained within
* this AppContext.
* @since 1.2
*/
public ThreadGroup getThreadGroup() {
return threadGroup;
}
/**
* Returns the context ClassLoader that was used to create this
* AppContext.
*
* @see java.lang.Thread#getContextClassLoader
*/
public ClassLoader getContextClassLoader() {
return contextClassLoader;
}
/**
* Returns a string representation of this AppContext.
* @since 1.2
*/
@Override
public String toString() {
return getClass().getName() + "[threadGroup=" + threadGroup.getName() + "]";
}
/**
* Returns an array of all the property change listeners
* registered on this component.
*
* @return all of this component's PropertyChangeListeners
* or an empty array if no property change
* listeners are currently registered
*
* @see #addPropertyChangeListener
* @see #removePropertyChangeListener
* @see #getPropertyChangeListeners(java.lang.String)
* @see java.beans.PropertyChangeSupport#getPropertyChangeListeners
* @since 1.4
*/
public synchronized PropertyChangeListener[] getPropertyChangeListeners() {
if (changeSupport == null) {
return new PropertyChangeListener[0];
}
return changeSupport.getPropertyChangeListeners();
}
/**
* Adds a PropertyChangeListener to the listener list for a specific
* property. The specified property may be one of the following:
*
*
*
*
* PropertyChangeListeners associated with
* the named property or an empty array if no listeners have
* been added
*
* @see #addPropertyChangeListener(java.lang.String, java.beans.PropertyChangeListener)
* @see #removePropertyChangeListener(java.lang.String, java.beans.PropertyChangeListener)
* @see #getPropertyChangeListeners
* @since 1.4
*/
public synchronized PropertyChangeListener[] getPropertyChangeListeners(
String propertyName) {
if (changeSupport == null) {
return new PropertyChangeListener[0];
}
return changeSupport.getPropertyChangeListeners(propertyName);
}
}
final class MostRecentKeyValue {
Object key;
Object value;
MostRecentKeyValue(Object k, Object v) {
key = k;
value = v;
}
void setPair(Object k, Object v) {
key = k;
value = v;
}
}