Codified a common pattern into a helper class.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3784 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/presents/util/PersistingUnit.java

@@ -0,0 +1,101 @@
+//
+// $Id$
+//
+// Narya library - tools for developing networked games
+// Copyright (C) 2002-2005 Three Rings Design, Inc., All Rights Reserved
+// http://www.threerings.net/code/narya/
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.threerings.presents.util;
+
+import com.samskivert.io.PersistenceException;
+import com.samskivert.util.Invoker;
+
+import com.threerings.presents.Log;
+import com.threerings.presents.client.InvocationService;
+import com.threerings.presents.data.InvocationCodes;
+
+/**
+ * Simplifies a common pattern which is to post an {@link Invoker} unit which
+ * does some database operation and then calls back to an {@link
+ * InvocationService.InvocationListener} of some sort. If the database operation
+ * fails, the error will be logged and the result listener will be replied to
+ * with {@link InvocationCodes#INTERNAL_ERROR}.
+ */
+public abstract class PersistingUnit extends Invoker.Unit
+{
+    public PersistingUnit (InvocationService.InvocationListener listener)
+    {
+        _listener = listener;
+    }
+
+    /**
+     * This method is where the unit performs its persistent actions. Any
+     * persistence exception will be caught and logged along with the output
+     * from {@link #getFailureMessage}, if any.
+     */
+    public abstract void invokePersistent ()
+        throws PersistenceException;
+
+    /**
+     * Handles the success case, which by default is to do nothing.
+     */
+    public void handleSuccess ()
+    {
+    }
+
+    /**
+     * Handles the failure case by logging the error and reporting an internal
+     * error to the listener.
+     */
+    public void handleFailure (PersistenceException error)
+    {
+        Log.warning(getFailureMessage());
+        Log.logStackTrace(error);
+        _listener.requestFailed(InvocationCodes.INTERNAL_ERROR);
+    }
+
+    /**
+     * Provides a custom failure message in the event that the persistent
+     * action fails. This will be logged along with the exception.
+     */
+    public String getFailureMessage ()
+    {
+        return this + " failed.";
+    }
+
+    public boolean invoke ()
+    {
+        try {
+            invokePersistent();
+        } catch (PersistenceException pe) {
+            _error = pe;
+        }
+        return true;
+    }
+
+    public void handleResult ()
+    {
+        if (_error != null) {
+            handleFailure(_error);
+        } else {
+            handleSuccess();
+        }
+    }
+
+    protected InvocationService.InvocationListener _listener;
+    protected PersistenceException _error;
+}