tools/org.eclipse.persistence.tools.utility/src/org/eclipse/persistence/tools/utility/BidiStringConverter.java

/*******************************************************************************
 * Copyright (c) 2007, 2012 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation
 *
 ******************************************************************************/
package org.eclipse.persistence.tools.utility;

import java.io.Serializable;

/**
 * Used by various "pluggable" classes to transform objects
 * into strings and vice versa.
 *
 * If anyone can come up with a better class name
 * and/or method name, I would love to hear it.  ~bjv
 */
public interface BidiStringConverter<T> extends StringConverter<T> {

	/**
	 * Converts the specified string into an object. The semantics of "convert to object" is
	 * determined by the contract between the client and the server. Typically, if the string is
	 * <code>null</code>, <code>null</code> is returned.
	 */
	T convertToObject(String value);

	final class BooleanConverter implements BidiStringConverter<Boolean>, Serializable {
		public static final BidiStringConverter<Boolean> INSTANCE = new BooleanConverter();
		private static final long serialVersionUID = 1L;
		// ensure single instance
		private BooleanConverter() {
			super();
		}
		public static BidiStringConverter<Boolean> instance() {
			return INSTANCE;
		}
		/** * Returns Boolean.FALSE. */
		@Override
		public Boolean convertToObject(String s) {
			return (s == null) ? null : Boolean.valueOf(s);
		}
		/** * Returns "false". */
		@Override
		public String convertToString(Boolean b) {
			return (b == null) ? null : b.toString();
		}
		private Object readResolve() {
			// replace this object with the singleton
			return INSTANCE;
		}
		@Override
		public String toString() {
			return StringTools.buildSingletonToString(this);
		}
	}

	final class Default<S> implements BidiStringConverter<S>, Serializable {
		@SuppressWarnings("rawtypes")
		public static final BidiStringConverter INSTANCE = new Default();
		private static final long serialVersionUID = 1L;
		// ensure single instance
		private Default() {
			super();
		}
		@SuppressWarnings("unchecked")
		public static <R> BidiStringConverter<R> instance() {
			return INSTANCE;
		}
		// * Returns the string
		@Override
		@SuppressWarnings("unchecked")
		public S convertToObject(String s) {
			return (S) s;
		}
		// * Returns the object's #toString() result
		@Override
		public String convertToString(S o) {
			return (o == null) ? null : o.toString();
		}
		private Object readResolve() {
			// replace this object with the singleton
			return INSTANCE;
		}
		@Override
		public String toString() {
			return StringTools.buildSingletonToString(this);
		}
	}

	final class Disabled<S> implements BidiStringConverter<S>, Serializable {
		@SuppressWarnings("rawtypes")
		public static final BidiStringConverter INSTANCE = new Disabled();
		private static final long serialVersionUID = 1L;
		// ensure single instance
		private Disabled() {
			super();
		}
		@SuppressWarnings("unchecked")
		public static <R> BidiStringConverter<R> instance() {
			return INSTANCE;
		}
		// throw an exception
		@Override
		public S convertToObject(String s) {
			throw new UnsupportedOperationException();
		}
		// throw an exception
		@Override
		public String convertToString(S o) {
			throw new UnsupportedOperationException();
		}
		private Object readResolve() {
			// replace this object with the singleton
			return INSTANCE;
		}
		@Override
		public String toString() {
			return StringTools.buildSingletonToString(this);
		}
	}

	final class IntegerConverter implements BidiStringConverter<Integer>, Serializable {
		public static final BidiStringConverter<Integer> INSTANCE = new IntegerConverter();
		private static final long serialVersionUID = 1L;
		// ensure single instance
		private IntegerConverter() {
			super();
		}
		public static BidiStringConverter<Integer> instance() {
			return INSTANCE;
		}
		/** Convert the string to an Integer, if possible. */
		@Override
		public Integer convertToObject(String s) {
			return (s == null) ? null : Integer.valueOf(s);
		}
		/** Integer's #toString() works well. */
		@Override
		public String convertToString(Integer integer) {
			return (integer == null) ? null : integer.toString();
		}
		private Object readResolve() {
			// replace this object with the singleton
			return INSTANCE;
		}
		@Override
		public String toString() {
			return StringTools.buildSingletonToString(this);
		}
	}
}