Added a ResultHandler class to store results after they've been

returned.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@2074 6335cc39-0255-0410-8fd6-9bcaacd3b74c

src/java/com/samskivert/util/ResultHandler.java

@@ -0,0 +1,52 @@
+//
+// $Id: ResultListener.java,v 1.1 2002/03/20 07:07:48 mdb Exp $
+
+package com.samskivert.util;
+
+/**
+ * Acts as a {@link ResultListenerList} until the result (or cause of failure) is received,
+ * after which {@link #getResult} provides the result immediately.  This is most useful for
+ * caches in which multiple listeners may request the result while it is resolving.
+ */
+public class ResultHandler<T>
+    implements ResultListener<T>
+{
+    /**
+     * Retrieves the result for the specified listener.  If the result is already available (or the
+     * request failed), the listener will receive an immediate response.  Otherwise, the listener
+     * will be added to the list and notified when the result is available.
+     */
+    public void getResult (ResultListener<T> rl)
+    {
+        if (_result != null) {
+            rl.requestCompleted(_result);
+        } else if (_error != null) {
+            rl.requestFailed(_error);
+        } else { // _list != null
+            _list.add(rl);
+        }
+    }
+
+    // documentation inherited from interface ResultListener
+    public void requestCompleted (T result)
+    {
+        _list.requestCompleted(_result = result);
+        _list = null;
+    }
+
+    // documentation inherited from interface ResultListener
+    public void requestFailed (Exception cause)
+    {
+        _list.requestFailed(_error = cause);
+        _list = null;
+    }
+
+    /** When waiting for the result, the list of registered listeners. */
+    protected ResultListenerList<T> _list = new ResultListenerList<T>();
+
+    /** The result, if it was obtained successfully. */
+    protected T _result;
+
+    /** The cause of the failure, if the result could not be obtained. */
+    protected Exception _error;
+}