converters.java

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/*
 * @(#)Converters.java	1.16 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, 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  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package sun.io;

import java.io.UnsupportedEncodingException;
import java.lang.ref.SoftReference;
import java.util.Properties;

/**
 * Package-private utility class that caches the default converter classes and
 * provides other logic common to both the ByteToCharConverter and
 * CharToByteConverter classes.
 *
 * @author   Mark Reinhold
 * @version  1.7, 00/07/07
 * @since    JDK1.2
 */

public class Converters {

    private Converters() { }	/* To prevent instantiation */

    /* Lock for all static fields in this class */
    private static Object lock = Converters.class;

    /* Cached values of system properties */
    private static String converterPackageName = null;  /* file.encoding.pkg */
    private static String defaultEncoding = null;       /* file.encoding */

    /* Converter type constants and names */
    public static final int BYTE_TO_CHAR = 0;
    public static final int CHAR_TO_BYTE = 1;
    private static final String[] converterPrefix = { "ByteToChar",
						      "CharToByte" };

    private static final int CACHE_SIZE = 3;

    /* For the default charset, whatever it turns out to be */
    private static final Object DEFAULT_NAME = new Object();

    /* Cached converter classes, CACHE_SIZE per converter type.  Each cache
     * entry is a soft reference to a two-object array; the first element of
     * the array is the converter class, the second is an object (typically a
     * string) representing the encoding name that was used to request the
     * converter, e.g.,
     *
     *     ((Object[])classCache[CHAR_TO_BYTE][i].get())[0]
     *
     * will be a CharToByteConverter and
     *
     *     ((Object[])classCache[CHAR_TO_BYTE][i].get())[1]
     *
     * will be the string encoding name used to request it, assuming that cache
     * entry i is valid.
     *
     * Ordinarily we'd do this with a private static utility class, but since
     * this code can be involved in the startup sequence it's important to keep
     * the footprint down.
     */
    private static SoftReference[][] classCache
	= new SoftReference[][] {
	    new SoftReference[CACHE_SIZE],
	    new SoftReference[CACHE_SIZE]
	};

    private static void moveToFront(Object[] oa, int i) {
	Object ob = oa[i];
	for (int j = i; j > 0; j--)
	    oa[j] = oa[j - 1];
	oa[0] = ob;
    }

    private static Class cache(int type, Object encoding) {
	SoftReference[] srs = classCache[type];
	for (int i = 0; i < CACHE_SIZE; i++) {
	    SoftReference sr = srs[i];
	    if (sr == null)
		continue;
	    Object[] oa = (Object[])sr.get();
	    if (oa == null) {
		srs[i] = null;
		continue;
	    }
	    if (oa[1].equals(encoding)) {
		moveToFront(srs, i);
		return (Class)oa[0];
	    }
	}
	return null;
    }

    private static Class cache(int type, Object encoding, Class c) {
	SoftReference[] srs = classCache[type];
	srs[CACHE_SIZE - 1] = new SoftReference(new Object[] { c, encoding });
	moveToFront(srs, CACHE_SIZE - 1);
	return c;
    }

    /* Used to avoid doing expensive charset lookups for charsets that are not
     * yet directly supported by NIO.
     */
    public static boolean isCached(int type, String encoding) {
	synchronized (lock) {
	    SoftReference[] srs = classCache[type];
	    for (int i = 0; i < CACHE_SIZE; i++) {
		SoftReference sr = srs[i];
		if (sr == null)
		    continue;
		Object[] oa = (Object[])sr.get();
		if (oa == null) {
		    srs[i] = null;
		    continue;
		}
		if (oa[1].equals(encoding))
		    return true;
	    }
	    return false;
	}
    }



    /** Get the name of the converter package */
    private static String getConverterPackageName() {
	String cp = converterPackageName;
	if (cp != null) return cp;
	java.security.PrivilegedAction pa =
	    new sun.security.action.GetPropertyAction("file.encoding.pkg");
	cp = (String)java.security.AccessController.doPrivileged(pa);
	if (cp != null) {
	    /* Property is set, so take it as the true converter package */
	    converterPackageName = cp;
	} else {
	    /* Fall back to sun.io */
	    cp = "sun.io";
	}
	return cp;
    }

    public static String getDefaultEncodingName() {
	synchronized (lock) {
	    if (defaultEncoding == null) {
		java.security.PrivilegedAction pa =
		    new sun.security.action.GetPropertyAction("file.encoding");
		defaultEncoding = (String)java.security.AccessController.doPrivileged(pa);
	    }
	}
	return defaultEncoding;
    }

    public static void resetDefaultEncodingName() {
	// This method should only be called during VM initialization.
	synchronized (lock) {
	    defaultEncoding = "ISO-8859-1";
	    Properties p = System.getProperties();
	    p.setProperty("file.encoding", defaultEncoding);
	    System.setProperties(p);
	}
    }

    /**
     * Get the class that implements the given type of converter for the named
     * encoding, or throw an UnsupportedEncodingException if no such class can
     * be found
     */
    private static Class getConverterClass(int type, String encoding)
	throws UnsupportedEncodingException
    {
	String enc = null;

	/* "ISO8859_1" is the canonical name for the ISO-Latin-1 encoding.
	   Native code in the JDK commonly uses the alias "8859_1" instead of
	   "ISO8859_1".  We hardwire this alias here in order to avoid loading
	   the full alias table just for this case. */
	if (!encoding.equals("ISO8859_1")) {
	    if (encoding.equals("8859_1")) {
		enc = "ISO8859_1";
	    /*
	     * On Solaris with nl_langinfo() called in GetJavaProperties():
	     *
	     *   locale undefined -> NULL -> hardcoded default
	     *   "C" locale       -> "" -> hardcoded default	(on 2.6)
	     *   "C" locale       -> "646" 			(on 2.7)
	     *   "en_US" locale -> "ISO8859-1"
	     *   "en_GB" locale -> "ISO8859-1"			(on 2.7)
	     *   "en_UK" locale -> "ISO8859-1"			(on 2.6)
	     */
	    } else if (encoding.equals("ISO8859-1")) {
		enc = "ISO8859_1";
	    } else if (encoding.equals("646")) {
		enc = "ASCII";
	    } else {
		enc = CharacterEncoding.aliasName(encoding);
	    }
	}
	if (enc == null) {
	    enc = encoding;
	}

	try {
	    return Class.forName(getConverterPackageName()
				 + "." + converterPrefix[type] + enc);
	} catch(ClassNotFoundException e) {
	    throw new UnsupportedEncodingException(enc);
	}

    }

    /**
     * Instantiate the given converter class, or throw an
     * UnsupportedEncodingException if it cannot be instantiated
     */
    private static Object newConverter(String enc, Class c)
	throws UnsupportedEncodingException
    {
	try {
	    return c.newInstance();
	} catch(InstantiationException e) {
	    throw new UnsupportedEncodingException(enc);
	} catch(IllegalAccessException e) {
	    throw new UnsupportedEncodingException(enc);
	}
    }

    /**
     * Create a converter object that implements the given type of converter
     * for the given encoding, or throw an UnsupportedEncodingException if no
     * appropriate converter class can be found and instantiated
     */
    static Object newConverter(int type, String enc)
	throws UnsupportedEncodingException
    {
	Class c;
	synchronized (lock) {
	    c = cache(type, enc);
	    if (c == null) {
		c = getConverterClass(type, enc);
		cache(type, enc, c);
	    }
	}
	return newConverter(enc, c);
    }

    /**
     * Find the class that implements the given type of converter for the
     * default encoding.  If the default encoding cannot be determined or is
     * not yet defined, return a class that implements the fallback default
     * encoding, which is just ISO 8859-1.
     */
    private static Class getDefaultConverterClass(int type) {
	boolean fillCache = false;
	Class c;

	/* First check the class cache */
	c = cache(type, DEFAULT_NAME);
	if (c != null)
	    return c;

	/* Determine the encoding name */
	String enc = getDefaultEncodingName();
	if (enc != null) {
	    /* file.encoding has been set, so cache the converter class */
	    fillCache = true;
	} else {
	    /* file.encoding has not been set, so use a default encoding which
	       will not be cached */
	    enc = "ISO8859_1";
	}

	/* We have an encoding name; try to find its class */
	try {
	    c = getConverterClass(type, enc);
	    if (fillCache) {
		cache(type, DEFAULT_NAME, c);
	    }
	} catch (UnsupportedEncodingException x) {
	    /* Can't find the default class, so fall back to ISO 8859-1 */
	    try {
		c = getConverterClass(type, "ISO8859_1");
	    } catch (UnsupportedEncodingException y) {
		throw new InternalError("Cannot find default "
                                        + converterPrefix[type]
					+ " converter class");
	    }
	}
	return c;

    }

    /**
     * Create a converter object that implements the given type of converter
     * for the default encoding, falling back to ISO 8859-1 if the default
     * encoding cannot be determined.
     */
    static Object newDefaultConverter(int type) {
	Class c;
	synchronized (lock) {
	    c = getDefaultConverterClass(type);
	}
	try {
	    return newConverter("", c);
	} catch (UnsupportedEncodingException x) {
	    throw new InternalError("Cannot instantiate default converter"
				    + " class " + c.getName());
	}
    }

}