Examples of ae.sun.awt.AppContext

ae.sun.awt.AppContext
The AppContext is a table referenced by ThreadGroup which stores application service instances. (If you are not writing an application service, or don't know what one is, please do not use this class.) The AppContext allows applet access to what would otherwise be potentially dangerous services, such as the ability to peek at EventQueues or change the look-and-feel of a Swing application.
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 ae.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

            }
        }
    }


    private synchronized void initContext() {
        final AppContext context = AppContext.getAppContext();


        if (contentsContext != context) {
            // Need to synchronize on the AppContext to guarantee that it cannot
            // be disposed after the check, but before the listener is added.
            synchronized (context) {
                if (context.isDisposed()) {
                    throw new IllegalStateException("Can't set contents from disposed AppContext");
                }
                context.addPropertyChangeListener
                    (AppContext.DISPOSED_PROPERTY_NAME, this);
            }
            if (contentsContext != null) {
                contentsContext.removePropertyChangeListener
                    (AppContext.DISPOSED_PROPERTY_NAME, this);

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     * @return the contents of this clipboard if it has been set from the same
     *         AppContext as it is currently retrieved or null otherwise
     * @since 1.5
     */
    private synchronized Transferable getContextContents() {
        AppContext context = AppContext.getAppContext();
        return (context == contentsContext) ? contents : null;
    }

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    public abstract long getID();


    public void propertyChange(PropertyChangeEvent evt) {
        if (AppContext.DISPOSED_PROPERTY_NAME.equals(evt.getPropertyName()) &&
            Boolean.TRUE.equals(evt.getNewValue())) {
            final AppContext disposedContext = (AppContext)evt.getSource();
            lostOwnershipLater(disposedContext);
        }
    }

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     * @param disposedContext the AppContext that is disposed or
     *        <code>null</code> if the ownership is lost because another
     *        application acquired ownership.
     */
    protected void lostOwnershipLater(final AppContext disposedContext) {
        final AppContext context = this.contentsContext;
        if (context == null) {
            return;
        }


        final Runnable runnable = new Runnable() {
                public void run() {
                    final SunClipboard sunClipboard = SunClipboard.this;
                    ClipboardOwner owner = null;
                    Transferable contents = null;


                    synchronized (sunClipboard) {
                        final AppContext context = sunClipboard.contentsContext;


                        if (context == null) {
                            return;
                        }


                        if (disposedContext == null || context == disposedContext) {
                            owner = sunClipboard.owner;
                            contents = sunClipboard.contents;
                            sunClipboard.contentsContext = null;
                            sunClipboard.owner = null;
                            sunClipboard.contents = null;
                            sunClipboard.clearNativeContext();
                            context.removePropertyChangeListener
                                (AppContext.DISPOSED_PROPERTY_NAME, sunClipboard);
                        } else {
                            return;
                        }
                    }

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                                        }
                                    },
                                    lock,
                                    true);


        AppContext requesterAppContext = SunToolkit.targetToAppContext(requester);
        synchronized (lock) {
            SunToolkit.postEvent(requesterAppContext, event);
            lock.wait();
        }

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      */
    private static void createFetchers(final FetcherInfo info) {
       // We need to instantiate a new ImageFetcher thread.
       // First, figure out which ThreadGroup we'll put the
       // new ImageFetcher into
       final AppContext appContext = AppContext.getAppContext();
       ThreadGroup threadGroup = appContext.getThreadGroup();
       ThreadGroup fetcherThreadGroup;
       try {
          if (threadGroup.getParent() != null) {
             // threadGroup is not the root, so we proceed
             fetcherThreadGroup = threadGroup;
          } else {
             // threadGroup is the root ("system") ThreadGroup.
             // We instead want to use its child: the "main"
             // ThreadGroup.  Thus, we start with the current
             // ThreadGroup, and go up the tree until
             // threadGroup.getParent().getParent() == null.
             threadGroup = Thread.currentThread().getThreadGroup();
             ThreadGroup parent = threadGroup.getParent();
             while ((parent != null)
                  && (parent.getParent() != null)) {
                  threadGroup = parent;
                  parent = threadGroup.getParent();
             }
             fetcherThreadGroup = threadGroup;
         }
       } catch (SecurityException e) {
         // Not allowed access to parent ThreadGroup -- just use
         // the AppContext's ThreadGroup
         fetcherThreadGroup = appContext.getThreadGroup();
       }
       final ThreadGroup fetcherGroup = fetcherThreadGroup;


       java.security.AccessController.doPrivileged(
         new java.security.PrivilegedAction() {

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    /* The key to put()/get() the FetcherInfo into/from the AppContext. */
    private static final Object FETCHER_INFO_KEY =
                                        new StringBuffer("FetcherInfo");


    static FetcherInfo getFetcherInfo() {
        AppContext appContext = AppContext.getAppContext();
        synchronized(appContext) {
            FetcherInfo info = (FetcherInfo)appContext.get(FETCHER_INFO_KEY);
            if (info == null) {
                info = new FetcherInfo();
                appContext.put(FETCHER_INFO_KEY, info);
            }
            return info;
        }
    }

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                        done = true;
                    }
                }
            };


            final AppContext appContext = SunToolkit.targetToAppContext(source);


            getToolkitThreadBlockedHandler().lock();


            if (appContext != null) {
                appContext.put(DATA_CONVERTER_KEY, dataConverter);
            }


            SunToolkit.executeOnEventHandlerThread(source, dataConverter);


            while (stack.empty()) {
                getToolkitThreadBlockedHandler().enter();
            }


            if (appContext != null) {
                appContext.remove(DATA_CONVERTER_KEY);
            }


            ret = (byte[])stack.pop();
        } finally {
            getToolkitThreadBlockedHandler().unlock();

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        return ret;
    }


    public void processDataConversionRequests() {
        if (EventQueue.isDispatchThread()) {
            AppContext appContext = AppContext.getAppContext();
            getToolkitThreadBlockedHandler().lock();
            try {
                Runnable dataConverter =
                    (Runnable)appContext.get(DATA_CONVERTER_KEY);
                if (dataConverter != null) {
                    dataConverter.run();
                    appContext.remove(DATA_CONVERTER_KEY);
                }
            } finally {
                getToolkitThreadBlockedHandler().unlock();
            }
        }

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    public synchronized void addFlavorListener(FlavorListener listener) {
        if (listener == null) {
            return;
        }
        AppContext appContext = AppContext.getAppContext();
        EventListenerAggregate contextFlavorListeners = (EventListenerAggregate)
                appContext.get(CLIPBOARD_FLAVOR_LISTENER_KEY);
        if (contextFlavorListeners == null) {
            contextFlavorListeners = new EventListenerAggregate(FlavorListener.class);
            appContext.put(CLIPBOARD_FLAVOR_LISTENER_KEY, contextFlavorListeners);
        }
        contextFlavorListeners.add(listener);


        if (numberOfFlavorListeners++ == 0) {
            long[] currentFormats = null;

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ae.java.awt.KeyboardFocusManager

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