001/*
002 *   Copyright (C) Christian Schulte, 2012-22
003 *   All rights reserved.
004 *
005 *   Redistribution and use in source and binary forms, with or without
006 *   modification, are permitted provided that the following conditions
007 *   are met:
008 *
009 *     o Redistributions of source code must retain the above copyright
010 *       notice, this list of conditions and the following disclaimer.
011 *
012 *     o Redistributions in binary form must reproduce the above copyright
013 *       notice, this list of conditions and the following disclaimer in
014 *       the documentation and/or other materials provided with the
015 *       distribution.
016 *
017 *   THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
018 *   INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
019 *   AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
020 *   THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY DIRECT, INDIRECT,
021 *   INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
022 *   NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
023 *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
024 *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
025 *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
026 *   THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
027 *
028 *   $JOMC: ModelContextFactory.java 4613 2012-09-22 10:07:08Z schulte $
029 *
030 */
031package org.jomc.modlet;
032
033import java.security.AccessController;
034import java.security.PrivilegedAction;
035import java.text.MessageFormat;
036import java.util.Locale;
037import java.util.ResourceBundle;
038
039/**
040 * Interface to creating model contexts.
041 *
042 * @author <a href="mailto:cs@schulte.it">Christian Schulte</a>
043 * @version $JOMC: ModelContextFactory.java 4613 2012-09-22 10:07:08Z schulte $
044 * @since 1.2
045 */
046public abstract class ModelContextFactory
047{
048
049    /** Constant for the name of the default {@code ModelContextFactory} implementation. */
050    private static final String DEFAULT_MODEL_CONTEXT_FACTORY_CLASS_NAME = "org.jomc.modlet.DefaultModelContextFactory";
051
052    /** Constant for the name of the system property controlling {@code ModelContextFactory} implementations. */
053    private static final String MODEL_CONTEXT_FACTORY_CLASS_NAME_PROPERTY =
054        "org.jomc.modlet.ModelContextFactory";
055
056    /** Creates a new {@code ModelContextFactory} instance. */
057    protected ModelContextFactory()
058    {
059        super();
060    }
061
062    /**
063     * Creates a new {@code ModelContextFactory} instance.
064     * <p>The name of the class providing the {@code ModelContextFactory} implementation loaded by this method is
065     * controlled by system property {@code org.jomc.modlet.ModelContextFactory}. If that property is not set, this
066     * methods returns a new default instance.</p>
067     *
068     * @return A new {@code ModelContextFactory} instance.
069     *
070     * @throws ModelContextFactoryError if creating a new instance fails.
071     */
072    public static ModelContextFactory newInstance() throws ModelContextFactoryError
073    {
074        return newInstance( AccessController.doPrivileged( new PrivilegedAction<String>()
075        {
076
077            public String run()
078            {
079                return System.getProperty( MODEL_CONTEXT_FACTORY_CLASS_NAME_PROPERTY,
080                                           DEFAULT_MODEL_CONTEXT_FACTORY_CLASS_NAME );
081
082            }
083
084        } ) );
085    }
086
087    /**
088     * Creates a new {@code ModelContextFactory} instance.
089     *
090     * @param factoryClassName The name of the {@code ModelContextFactory} class to create an instance of.
091     *
092     * @return A new {@code ModelContextFactory} instance.
093     *
094     * @throws NullPointerException if {@code factoryClassName} is {@code null}.
095     * @throws ModelContextFactoryError if creating a new instance fails.
096     */
097    public static ModelContextFactory newInstance( final String factoryClassName ) throws ModelContextFactoryError
098    {
099        if ( factoryClassName == null )
100        {
101            throw new NullPointerException( "factoryClassName" );
102        }
103
104        try
105        {
106            final Class<?> factoryClass = Class.forName( factoryClassName );
107
108            if ( !ModelContextFactory.class.isAssignableFrom( factoryClass ) )
109            {
110                throw new ModelContextFactoryError( getMessage( "illegalFactory", factoryClassName,
111                                                                ModelContextFactory.class.getName() ) );
112
113            }
114
115            return factoryClass.asSubclass( ModelContextFactory.class ).newInstance();
116        }
117        catch ( final ClassNotFoundException e )
118        {
119            throw new ModelContextFactoryError( getMessage( "classNotFound", factoryClassName ), e );
120        }
121        catch ( final InstantiationException e )
122        {
123            final String message = getMessage( e );
124            throw new ModelContextFactoryError( getMessage( "instantiationException", factoryClassName,
125                                                            message != null ? " " + message : "" ), e );
126
127        }
128        catch ( final IllegalAccessException e )
129        {
130            final String message = getMessage( e );
131            throw new ModelContextFactoryError( getMessage( "accessDenied", factoryClassName,
132                                                            message != null ? " " + message : "" ), e );
133
134        }
135    }
136
137    /**
138     * Creates a new {@code ModelContext} instance.
139     *
140     * @return A new {@code ModelContext} instance.
141     */
142    public abstract ModelContext newModelContext();
143
144    /**
145     * Creates a new {@code ModelContext} instance.
146     *
147     * @param classLoader The class loader to create a new instance with or {@code null}, to create a new instance
148     * using the bootstrap class loader.
149     *
150     * @return A new {@code ModelContext} instance for {@code classLoader}.
151     */
152    public abstract ModelContext newModelContext( final ClassLoader classLoader );
153
154    private static String getMessage( final String key, final Object... args )
155    {
156        return MessageFormat.format( ResourceBundle.getBundle( ModelContextFactory.class.getName().replace( '.', '/' ),
157                                                               Locale.getDefault() ).getString( key ), args );
158
159    }
160
161    private static String getMessage( final Throwable t )
162    {
163        return t != null ? t.getMessage() != null ? t.getMessage() : getMessage( t.getCause() ) : null;
164    }
165
166}