Implement In-Memory Preferences

core/framework/src/main/java/org/phoebus/framework/preferences/InMemoryPreferences.java

@@ -0,0 +1,111 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Oak Ridge National Laboratory.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *******************************************************************************/
+package org.phoebus.framework.preferences;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.prefs.AbstractPreferences;
+import java.util.prefs.BackingStoreException;
+import java.util.prefs.Preferences;
+
+/** Java Preferences that are held in memory, not persisted
+ *  @author Kay Kasemir
+ */
+class InMemoryPreferences extends AbstractPreferences
+{
+    /** Preferences for both "user" and "system" */
+    private static final InMemoryPreferences prefs = new InMemoryPreferences(null, "");
+
+    /** Settings for this node in the preferences hierarchy */
+    private ConcurrentHashMap<String, String> cache = new ConcurrentHashMap<>();
+
+    /** @return User preferences */
+    public static Preferences getUserRoot()
+    {
+        return prefs;
+    }
+
+    /** @return System preferences */
+    public static Preferences getSystemRoot()
+    {
+        return prefs;
+    }
+
+    InMemoryPreferences(final InMemoryPreferences parent, final String name)
+    {
+        super(parent, name);
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected void putSpi(String key, String value)
+    {
+        cache.put(key, value);
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected String getSpi(String key)
+    {
+        return cache.get(key);
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected void removeSpi(String key)
+    {
+        cache.remove(key);        
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected void removeNodeSpi() throws BackingStoreException
+    {
+        // Nothing to remove in the file system
+        cache.clear();
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected String[] keysSpi() throws BackingStoreException
+    {
+        return cache.keySet().toArray(new String[cache.size()]);        
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected String[] childrenNamesSpi() throws BackingStoreException
+    {
+        // This method need not return the names of any nodes already cached
+        // by the AbstractPreferences
+        return new String[0];
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected AbstractPreferences childSpi(String name)
+    {
+        // AbstractPreferences guaranteed that the named node has not been returned
+        // by a previous invocation of this method or {@link #getChild(String)},
+        // so only called once and can then create the one and only new child
+        return new InMemoryPreferences(this, name);
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected void syncSpi() throws BackingStoreException
+    {
+        // Nothing to sync
+    }
+
+    /** @inheritDoc */
+    @Override
+    protected void flushSpi() throws BackingStoreException
+    {
+        // Nothing to sync
+    }
+}

core/framework/src/main/java/org/phoebus/framework/preferences/PhoebusPreferenceService.java

@@ -22,13 +22,13 @@ public static Preferences userNodeForClass(final Class<?> clazz)
     @Override
     public Preferences userRoot()
     {
-        return FileSystemPreferences.getUserRoot();
+        return InMemoryPreferences.getUserRoot();
     }
 
     @Override
     public Preferences systemRoot()
     {
-        return FileSystemPreferences.getSystemRoot();
+        return InMemoryPreferences.getSystemRoot();
     }
 
 }