CrossCheckingMessageSource

/*
 * EL4J, the Extension Library for the J2EE, adds incremental enhancements to
 * the spring framework, http://el4j.sf.net
 * Copyright (C) 2006 by ELCA Informatique SA, Av. de la Harpe 22-24,
 * 1000 Lausanne, Switzerland, http://www.elca.ch
 *
 * EL4J is published under the GNU Lesser General Public License (LGPL)
 * Version 2.1. See http://www.gnu.org/licenses/
 *
 * 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.
 *
 * For alternative licensing, please contact info@elca.ch
 */
package ch.elca.el4j.services.i18n;

import java.util.Locale;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.MessageSource;
import org.springframework.context.MessageSourceResolvable;
import org.springframework.context.NoSuchMessageException;
import org.springframework.context.support.ResourceBundleMessageSource;

import ch.elca.el4j.util.codingsupport.Reject;

/**
 * Test class loading the same properties files in two or more message sources
 * and comparing their behavior.
 *
 * <h4> Usage </h4>
 * Replace the message source in the spring configuration with an instance of
 * this class (leaving the basenames-assignment intact) and configure the
 * types to be compared using {@link #m_types}. This class will then resolve
 * every
 * message it is asked to resolve from both sources, and {@code assert} they
 * agree about the message's value. (You should therefore enable assertions ...)
 *
 * @svnLink $Revision: 3874 $;$Date: 2009-08-04 14:25:40 +0200 (Di, 04. Aug 2009) $;$Author: swismer $;$URL: https://el4j.svn.sourceforge.net/svnroot/el4j/branches/el4j_3_1/el4j/framework/modules/core/src/main/java/ch/elca/el4j/services/i18n/CrossCheckingMessageSource.java $
 *
 * @author Adrian Moos (AMS)
 */
public class CrossCheckingMessageSource implements MessageSource,
	InitializingBean {

	/** The message sources to be compared. */
	MessageSource[] m_sources;

	/** The types of the message sources to be compared. */
	String[] m_types;

	/**
	 * Like {@link ResourceBundleMessageSource#setBasenames(String[])}.
	 */
	String[] m_basenames;

	/**
	 * Sets the types of the message sources to be compared.
	 */
	public void setTypes(String[] types) {
		m_types = types;
	}

	/**
	 * Like {@link ResourceBundleMessageSource#setBasenames(String[])}.
	 */
	public void setBasenames(String[] basenames) {
		m_basenames = basenames;
	}

	/** Represents a lookup's result. */
	static interface Result {
		/** Simulates the return of this result. */
		String ret();
	}

	/** The lookup found a message. */
	static class Found implements Result {
		/** The resolved message. */
		String m_message;

		/**
		 * Constructor.
		 * @param message The resolved message
		 */
		Found(String message) { m_message = message; }

		/** {@inheritDoc} */
		public String ret() { return m_message; }

		/** {@inheritDoc} */
		public int hashCode() {
			return m_message.hashCode();
		}

		/** {@inheritDoc} */
		public boolean equals(Object o) {
			return o instanceof Found
				&& m_message.equals(((Found) o).m_message);
		}
	}

	/** The lookup did not find a message. */
	static class NotFound implements Result {
		/** The exception that signaled the failure. */
		NoSuchMessageException m_e;

		/**
		 * Constructor.
		 * @param e The exception signaling the failure.
		 */
		NotFound(NoSuchMessageException e) { m_e = e; }

		/** {@inheritDoc} */
		public String ret() { throw m_e; }

		/** {@inheritDoc} */
		public int hashCode() {
			// Checkstyle: MagicNumber off
			return 0xdead;
			// Checkstyle: MagicNumber on
		}

		/** {@inheritDoc} */
		public boolean equals(Object o) {
			return o instanceof NotFound;
		}
	}

	/** Asserts that all lookup results are equal. */
	static class Checker {
		/** The result of the first lookup. */
		Result m_first;

		/** Checks a result. */
		void process(Result r) {
			if (m_first == null) {
				m_first = r;
			} else {
				assert m_first.equals(r);
			}
		}

		/** Simulates a lookup's result. */
		String get() {
			return m_first.ret();
		}
	}

	/** {@inheritDoc} */
	public String getMessage(MessageSourceResolvable resolvable, Locale locale)
		throws NoSuchMessageException {
		Checker c = new Checker();
		for (MessageSource ms : m_sources) {
			try {
				c.process(new Found(ms.getMessage(resolvable, locale)));
			} catch (NoSuchMessageException e) {
				c.process(new NotFound(e));
			}

		}
		return c.get();
	}

	/** {@inheritDoc} */
	public String getMessage(String code, Object[] args, Locale locale)
		throws NoSuchMessageException {
		Checker c = new Checker();
		for (MessageSource ms : m_sources) {
			try {
				c.process(new Found(ms.getMessage(code, args, locale)));
			} catch (NoSuchMessageException e) {
				c.process(new NotFound(e));
			}

		}
		return c.get();
	}

	/** {@inheritDoc} */
	public String getMessage(String code, Object[] args, String defaultMessage,
		Locale locale) {

		Checker c = new Checker();
		for (MessageSource ms : m_sources) {
			try {
				c.process(new Found(ms.getMessage(code, args, locale)));
			} catch (NoSuchMessageException e) {
				c.process(new NotFound(e));
			}

		}
		return c.get();
	}

	/** Creates and initializes the requested message sources. */
	public void afterPropertiesSet() throws Exception {
		m_sources = new MessageSource[m_types.length];
		for (int i = 0; i < m_types.length; i++) {
			MessageSource ms;
			try {
				ms = (MessageSource) Class.forName(m_types[i]).newInstance();
			} catch (Exception e) {
				throw new RuntimeException(e);
			}

			if (ms instanceof RewritingMessageSource) {
				((RewritingMessageSource) ms).setBasenames(m_basenames);
			} else if (ms instanceof ResourceBundleMessageSource) {
				((ResourceBundleMessageSource) ms).setBasenames(m_basenames);
			} else {
				Reject.ifCondition(true, "unsupported type");
			}
			m_sources[i] = ms;
		}
	}

}