Hibernate example source code file (ServiceLoader.java)

This example Hibernate source code file (ServiceLoader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Hibernate tags/keywords

arraylist, illegal, io, ioexception, ioexception, iterator, list, net, network, s, serviceconfigurationerror, serviceconfigurationerror, serviceloader, string, string, url, url, util

The Hibernate ServiceLoader.java source code

/*
 * 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.integrator.internal;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.ServiceConfigurationError;

import org.jboss.logging.Logger;

import org.hibernate.internal.CoreMessageLogger;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.classloading.spi.ClassLoaderService;

/**
 * @author Strong Liu
 */
final class ServiceLoader<S> implements Iterable {
	private static final CoreMessageLogger LOG = Logger.getMessageLogger(
			CoreMessageLogger.class, ServiceLoader.class.getName()
	);
	private static final String PREFIX = "META-INF/services/";
	private LinkedHashMap<String, S> providers = new LinkedHashMap();

	private ServiceLoader(Class<S> svc, ServiceRegistry serviceRegistry) {
		Class<S> service = svc;
		ClassLoaderService loader = serviceRegistry.getService( ClassLoaderService.class );
		String fullName = PREFIX + service.getName();
		service.getName();

		List<URL> configs = locateResources( loader, fullName );
		for ( URL url : configs ) {
			Iterator<String> names = parse( service, url );
			while ( names.hasNext() ) {
				String cn = names.next();
				try {
					S p = service.cast( loader.classForName( cn ).newInstance() );
					providers.put( cn, p );
				}
				catch ( Throwable x ) {
					fail( service, "Provider " + cn + " could not be instantiated: " + x, x );
				}
			}

		}
	}

	private List<URL> locateResources(ClassLoaderService loader, String fullName) {
		List<URL> urls = new ArrayList();
		urls.addAll( loader.locateResources( fullName ) );
		try {
			Enumeration<URL> hibUrls = ServiceLoader.class.getClassLoader().getResources( fullName );
			while ( hibUrls.hasMoreElements() ) {
				URL u = hibUrls.nextElement();
				if ( !urls.contains( u ) ) {
					urls.add( u );
				}

			}
		}
		catch ( IOException e ) {
			//ignore
		}
		return urls;
	}

	private static void fail(Class service, String msg, Throwable cause)
			throws ServiceConfigurationError {
		throw new ServiceConfigurationError(
				service.getName() + ": " + msg,
				cause
		);
	}

	private static void fail(Class service, String msg)
			throws ServiceConfigurationError {
		throw new ServiceConfigurationError( service.getName() + ": " + msg );
	}

	private static void fail(Class service, URL u, int line, String msg)
			throws ServiceConfigurationError {
		fail( service, u + ":" + line + ": " + msg );
	}

	// Parse a single line from the given configuration file, adding the name
	// on the line to the names list.
	//
	private int parseLine(Class service, URL u, BufferedReader r, int lc,
						  List<String> names)
			throws IOException, ServiceConfigurationError {
		String ln = r.readLine();
		if ( ln == null ) {
			return -1;
		}
		int ci = ln.indexOf( '#' );
		if ( ci >= 0 ) {
			ln = ln.substring( 0, ci );
		}
		ln = ln.trim();
		int n = ln.length();
		if ( n != 0 ) {
			if ( ( ln.indexOf( ' ' ) >= 0 ) || ( ln.indexOf( '\t' ) >= 0 ) ) {
				fail( service, u, lc, "Illegal configuration-file syntax" );
			}
			int cp = ln.codePointAt( 0 );
			if ( !Character.isJavaIdentifierStart( cp ) ) {
				fail( service, u, lc, "Illegal provider-class name: " + ln );
			}
			for ( int i = Character.charCount( cp ); i < n; i += Character.charCount( cp ) ) {
				cp = ln.codePointAt( i );
				if ( !Character.isJavaIdentifierPart( cp ) && ( cp != '.' ) ) {
					fail( service, u, lc, "Illegal provider-class name: " + ln );
				}
			}
			if ( !providers.containsKey( ln ) && !names.contains( ln ) ) {
				names.add( ln );
			}
		}
		return lc + 1;
	}

	private Iterator<String> parse(Class service, URL u)
			throws ServiceConfigurationError {
		InputStream in = null;
		BufferedReader r = null;
		ArrayList<String> names = new ArrayList();
		try {
			in = u.openStream();
			r = new BufferedReader( new InputStreamReader( in, "utf-8" ) );
			int lc = 1;
			while ( ( lc = parseLine( service, u, r, lc, names ) ) >= 0 ) {
				;
			}
		}
		catch ( IOException x ) {
			fail( service, "Error reading configuration file", x );
		}
		finally {
			try {
				if ( r != null ) {
					r.close();
				}
				if ( in != null ) {
					in.close();
				}
			}
			catch ( IOException y ) {
				fail( service, "Error closing configuration file", y );
			}
		}
		return names.iterator();
	}

	public Iterator<S> iterator() {
		return providers.values().iterator();

	}

	public static <S> ServiceLoader load(Class service,
											ServiceRegistry serviceRegistry) {
		return new ServiceLoader<S>( service, serviceRegistry );
	}


}