1 files changed, 95 insertions, 0 deletions
diff --git a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/Transformer.java b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/Transformer.java
new file mode 100644
index 0000000000..d95534e737
--- /dev/null
+++ b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/Transformer.java
@@ -0,0 +1,95 @@
+/*******************************************************************************
+ * Copyright (c) 2005, 2010 Oracle. 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.
+ * 
+ * Contributors:
+ *     Oracle - initial API and implementation
+ ******************************************************************************/
+package org.eclipse.jpt.common.utility.internal;
+
+import java.io.Serializable;
+
+/**
+ * Used by various "pluggable" classes to transform objects.
+ * Transform an object of type <code>T1</code> to an object of type
+ * <code>T2</code>.
+ * 
+ * @param <T1> the type of the object passed to the transformer
+ * @param <T2> the type of the object returned by the transformer
+ */
+public interface Transformer<T1, T2> {
+
+	/**
+	 * Return the transformed object.
+	 * The semantics of "transform" is determined by the
+	 * contract between the client and the server.
+	 */
+	T2 transform(T1 o);
+
+
+	/**
+	 * A "null" transformer will perform no transformation at all;
+	 * it will simply return the object "untransformed".
+	 */
+	final class Null<S1, S2> implements Transformer<S1, S2>, Serializable {
+		@SuppressWarnings("rawtypes")
+		public static final Transformer INSTANCE = new Null();
+		@SuppressWarnings("unchecked")
+		public static <R1, R2> Transformer<R1, R2> instance() {
+			return INSTANCE;
+		}
+		// ensure single instance
+		private Null() {
+			super();
+		}
+		// simply return the object, unchanged
+		@SuppressWarnings("unchecked")
+		public S2 transform(S1 o) {
+			return (S2) o;
+		}
+		@Override
+		public String toString() {
+			return "Transformer.Null"; //$NON-NLS-1$
+		}
+		private static final long serialVersionUID = 1L;
+		private Object readResolve() {
+			// replace this object with the singleton
+			return INSTANCE;
+		}
+	}
+
+	/**
+	 * A "disabled" transformer will throw an exception if
+	 * {@link #transform(Object)} is called. This is useful in situations
+	 * where a transformer is optional and the default transformer should
+	 * not be used.
+	 */
+	final class Disabled<S1, S2> implements Transformer<S1, S2>, Serializable {
+		@SuppressWarnings("rawtypes")
+		public static final Transformer INSTANCE = new Disabled();
+		@SuppressWarnings("unchecked")
+		public static <R1, R2> Transformer<R1, R2> instance() {
+			return INSTANCE;
+		}
+		// ensure single instance
+		private Disabled() {
+			super();
+		}
+		// throw an exception
+		public S2 transform(S1 o) {
+			throw new UnsupportedOperationException();
+		}
+		@Override
+		public String toString() {
+			return "Transformer.Disabled"; //$NON-NLS-1$
+		}
+		private static final long serialVersionUID = 1L;
+		private Object readResolve() {
+			// replace this object with the singleton
+			return INSTANCE;
+		}
+	}
+
+}