HHH-6333 - Create DeferredInitializationValue

hibernate-core/src/main/java/org/hibernate/internal/util/Value.java

@@ -0,0 +1,81 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * Copyright (c) 2011, Red Hat Inc. or third-party contributors as
+ * indicated by the @author tags or express copyright attribution
+ * statements applied by the authors.  All third-party contributions are
+ * distributed under license by Red Hat Inc.
+ *
+ * This copyrighted material is made available to anyone wishing to use, modify,
+ * copy, or redistribute it subject to the terms and conditions of the GNU
+ * Lesser General Public License, as published by the Free Software Foundation.
+ *
+ * This program 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 distribution; if not, write to:
+ * Free Software Foundation, Inc.
+ * 51 Franklin Street, Fifth Floor
+ * Boston, MA  02110-1301  USA
+ */
+package org.hibernate.internal.util;
+
+/**
+ * Represents a "final" value that is initialized either {@link #Value(Object) up front} or once at some point
+ * {@link #Value(org.hibernate.internal.util.Value.DeferredInitializer) after} declaration.
+ *
+ * @author Steve Ebersole
+ */
+public class Value<T> {
+
+	/**
+	 * The snippet that generates the initialization value.
+	 *
+	 * @param <T>
+	 */
+	public static interface DeferredInitializer<T> {
+		/**
+		 * Build the initialization value.
+		 * <p/>
+		 * Implementation note: returning {@code null} is "ok" but will cause this method to keep being called.
+		 *
+		 * @return The initialization value.
+		 */
+		public T initialize();
+	}
+
+	private final DeferredInitializer<T> valueInitializer;
+	private T value;
+
+	/**
+	 * Instantiates a {@link Value} with the specified initializer.
+	 *
+	 * @param valueInitializer The initializer to use in {@link #getValue} when value not yet known.
+	 */
+	public Value(DeferredInitializer<T> valueInitializer) {
+		this.valueInitializer = valueInitializer;
+	}
+
+	@SuppressWarnings( {"unchecked"})
+	public Value(T value) {
+		this( NO_DEFERRED_INITIALIZER );
+		this.value = value;
+	}
+
+	public T getValue() {
+		if ( value == null ) {
+			value = valueInitializer.initialize();
+		}
+		return value;
+	}
+
+	private static final DeferredInitializer NO_DEFERRED_INITIALIZER = new DeferredInitializer() {
+		@Override
+		public Void initialize() {
+			return null;
+		}
+	};
+}