. Added client config setting to allow the Shelf component to be hidden by default

. Added ExpiringValueCache class used to hold simple lists in the client that don't need refreshing constantly

git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@2105 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/cache/ExpiringValueCache.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2005 Alfresco, Inc.
+ *
+ * Licensed under the Mozilla Public License version 1.1 
+ * with a permitted attribution clause. You may obtain a
+ * copy of the License at
+ *
+ *   http://www.alfresco.org/legal/license.txt
+ *
+ * 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.alfresco.repo.cache;
+
+/**
+ * Simple cache of a single Object value.
+ * <p>
+ * The object placed in the cache will automatically be discarded after a timeout value.
+ * 
+ * @author Kevin Roast
+ */
+public class ExpiringValueCache<T>
+{
+    // default is to discard cached object after 1 minute
+    private final static long TIMEOUT_DEFAULT = 1000L*60L;
+    
+    private long timeout = TIMEOUT_DEFAULT;
+    private long snapshot = 0;
+    private T value;
+    
+    /**
+     * Default constructor.
+     * 
+     * Uses the default timeout of 1 minute.
+     */
+    public ExpiringValueCache()
+    {
+    }
+    
+    /**
+     * Constructor
+     * 
+     * @param timeout   Timeout in milliseconds before cached value is discarded
+     */
+    public ExpiringValueCache(long timeout)
+    {
+        this.timeout = timeout; 
+    }
+    
+    /**
+     * Put a value into the cache. The item will be return from the associated get() method
+     * until the timeout expires then null will be returned.
+     * 
+     * @param value     The object to store in the cache
+     */
+    public void put(T value)
+    {
+        this.value = value;
+        this.snapshot = System.currentTimeMillis();
+    }
+    
+    /**
+     * Get the cached object. The set item will be returned until it expires, then null will be returned.
+     *  
+     * @return cached object or null if not set or expired.
+     */
+    public T get()
+    {
+        if (snapshot + timeout < System.currentTimeMillis())
+        {
+            this.value = null;
+        }
+        return this.value;
+    }
+    
+    /**
+     * Clear the cache value
+     */
+    public void clear()
+    {
+        this.value = null;
+    }
+}