Importing upstream Jetty jetty-9.2.1.v20140609

[gigi.git] / lib / jetty / org / eclipse / jetty / util / Callback.java

diff --git a/lib/jetty/org/eclipse/jetty/util/Callback.java b/lib/jetty/org/eclipse/jetty/util/Callback.java
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+//
+//  ========================================================================
+//  Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
+//  ------------------------------------------------------------------------
+//  All rights reserved. This program and the accompanying materials
+//  are made available under the terms of the Eclipse Public License v1.0
+//  and Apache License v2.0 which accompanies this distribution.
+//
+//      The Eclipse Public License is available at
+//      http://www.eclipse.org/legal/epl-v10.html
+//
+//      The Apache License v2.0 is available at
+//      http://www.opensource.org/licenses/apache2.0.php
+//
+//  You may elect to redistribute this code under either of these licenses.
+//  ========================================================================
+//
+
+/*
+ * Copyright (c) 2012 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.eclipse.jetty.util;
+
+/**
+ * <p>A callback abstraction that handles completed/failed events of asynchronous operations.</p>
+ *
+ * <p>Semantically this is equivalent to an optimise Promise&lt;Void&gt;, but callback is a more meaningful 
+ * name than EmptyPromise</p>
+ */
+public interface Callback
+{
+    /**
+     * <p>Callback invoked when the operation completes.</p>
+     *
+     * @see #failed(Throwable)
+     */
+    public abstract void succeeded();
+
+    /**
+     * <p>Callback invoked when the operation fails.</p>
+     * @param x the reason for the operation failure
+     */
+    public void failed(Throwable x);
+
+    /**
+     * <p>Empty implementation of {@link Callback}</p>
+     */
+    public static class Adapter implements Callback
+    {
+        /**
+         * Instance of Adapter that can be used when the callback methods need an empty
+         * implementation without incurring in the cost of allocating a new Adapter object.
+         */
+        public static final Adapter INSTANCE = new Adapter();
+
+        @Override
+        public void succeeded()
+        {
+        }
+
+        @Override
+        public void failed(Throwable x)
+        {
+        }
+    }
+}