SquirrelJME/SquirrelJME

// -*- Mode: Java; indent-tabs-mode: t; tab-width: 4 -*-
// ---------------------------------------------------------------------------
// SquirrelJME
//     Copyright (C) Stephanie Gawroriski <xer@multiphasicapps.net>
// ---------------------------------------------------------------------------
// SquirrelJME is under the Mozilla Public License Version 2.0.
// See license.mkd for licensing and copyright information.
// ---------------------------------------------------------------------------

package java.util;

import cc.squirreljme.runtime.cldc.annotation.Api;

/**
 * The service loader is used to lookup services which may be defined in the
 * classpath.
 *
 * Services are stored as a list of class in resources within the JAR, these
 * services lists are declared in files specifying the class name. So the
 * format is {@code META-INF/services/fully.qualified.class.name}.
 *
 * The iterator may throw {@code ServiceConfigurationError}.
 *
 * @param <S> The class to provide a service for.
 * @since 2018/12/06
 */
@Api
public final class ServiceLoader<S>
    implements Iterable<S>
{
    /** The class to search for. */
    private final Class<S> _search;
    
    /** The service cache. */
    private final __ServiceLoaderCache__<S> _cache =
        new __ServiceLoaderCache__<S>();
    
    /**
     * Initializes the service loader.
     *
     * @param __cl The class to search.
     * @throws NullPointerException On null arguments.
     * @since 2018/12/06
     */
    @Api
    private ServiceLoader(Class<S> __cl)
        throws NullPointerException
    {
        if (__cl == null)
            throw new NullPointerException("NARG");
        
        this._search = __cl;
    }
    
    /**
     * {@inheritDoc}
     * @since 2018/12/06
     */
    @Override
    public Iterator<S> iterator()
    {
        Class<S> search = this._search;
        __ServiceLoaderCache__<S> cache = this._cache;
        
        // Use the cached array?
        Object[] use = cache._cache;
        if (use != null)
            return new __ServiceLoaderCachedIterator__<S>(search, use);
        
        // Cache it
        else
            return new __ServiceLoaderFreshIterator__<S>(search, cache);
    }
    
    /**
     * Clears the cache of services.
     *
     * @since 2018/12/06
     */
    @Api
    public void reload()
    {
        // Clear the cache
        this._cache._cache = null;
    }
    
    /**
     * {@inheritDoc}
     * @since 2018/12/06
     */
    @Override
    public String toString()
    {
        // Just matches what Java SE gives
        return "java.util.ServiceLoader[" + this._search.getName() + "]";
    }
    
    /**
     * Create a service loader for the given class.
     *
     * @param <S> The class to handle services for.
     * @param __cl The class to load a service for.
     * @return The service loader for this class.
     * @throws NullPointerException On null arguments.
     * @since 2018/12/06
     */
    @Api
    public static <S> ServiceLoader<S> load(Class<S> __cl)
        throws NullPointerException
    {
        if (__cl == null)
            throw new NullPointerException("NARG");
        
        return new ServiceLoader<S>(__cl);
    }
}