src/jdk.charsets/share/classes/sun/nio/cs/ext/AbstractCharsetProvider.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 in the LICENSE file that
 * accompanied this code).
 *
 * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.nio.cs.ext;

import java.lang.ref.SoftReference;
import java.nio.charset.Charset;
import java.nio.charset.spi.CharsetProvider;
import java.util.ArrayList;
import java.util.TreeMap;
import java.util.Iterator;
import java.util.Map;


/**
 * Abstract base class for charset providers.
 *
 * @author Mark Reinhold
 */

public class AbstractCharsetProvider
    extends CharsetProvider
{

    /* Maps canonical names to class names
     */
    private Map<String,String> classMap
        = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);

    /* Maps alias names to canonical names
     */
    private Map<String,String> aliasMap
        = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);

    /* Maps canonical names to alias-name arrays
     */
    private Map<String,String[]> aliasNameMap
        = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);

    /* Maps canonical names to soft references that hold cached instances
     */
    private Map<String,SoftReference<Charset>> cache
        = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);

    private String packagePrefix;

    protected AbstractCharsetProvider() {
        packagePrefix = "sun.nio.cs.";
    }

    protected AbstractCharsetProvider(String pkgPrefixName) {
        packagePrefix = pkgPrefixName.concat(".");
    }

    private static <K,V> void remove(Map<K,V> m, K name) {
        V x  = m.remove(name);
        assert (x != null);
    }

    /* Declare support for the given charset
     */
    protected void charset(String name, String className, String[] aliases) {
        synchronized (this) {
            classMap.putIfAbsent(name, className);
            for (int i = 0; i < aliases.length; i++)
                aliasMap.putIfAbsent(aliases[i], name);
            aliasNameMap.putIfAbsent(name, aliases);
            cache.clear();
        }
    }

    protected void deleteCharset(String name, String[] aliases) {
        synchronized (this) {
            remove(classMap, name);
            for (int i = 0; i < aliases.length; i++)
                remove(aliasMap, aliases[i]);
            remove(aliasNameMap, name);
            cache.clear();
        }
    }

    protected boolean hasCharset(String name) {
        synchronized (this) {
            return classMap.containsKey(name);
        }
    }

    /* Late initialization hook, needed by some providers
     */
    protected void init() { }

    private String canonicalize(String charsetName) {
        String acn = aliasMap.get(charsetName);
        return (acn != null) ? acn : charsetName;
    }

    private Charset lookup(String csn) {

        // Check cache first
        SoftReference<Charset> sr = cache.get(csn);
        if (sr != null) {
            Charset cs = sr.get();
            if (cs != null)
                return cs;
        }

        // Do we even support this charset?
        String cln = classMap.get(csn);

        if (cln == null)
            return null;

        // Instantiate the charset and cache it
        try {

            Class<?> c = Class.forName(packagePrefix.concat(cln),
                                       true,
                                       this.getClass().getClassLoader());

            @SuppressWarnings("deprecation")
            Charset cs = (Charset)c.newInstance();
            cache.put(csn, new SoftReference<Charset>(cs));
            return cs;
        } catch (ClassNotFoundException x) {
            return null;
        } catch (IllegalAccessException x) {
            return null;
        } catch (InstantiationException x) {
            return null;
        }
    }

    public final Charset charsetForName(String charsetName) {
        synchronized (this) {
            init();
            return lookup(canonicalize(charsetName));
        }
    }

    public final Iterator<Charset> charsets() {

        final ArrayList<String> ks;
        synchronized (this) {
            init();
            ks = new ArrayList<>(classMap.keySet());
        }

        return new Iterator<Charset>() {
                Iterator<String> i = ks.iterator();

                public boolean hasNext() {
                    return i.hasNext();
                }

                public Charset next() {
                    String csn = i.next();
                    synchronized (AbstractCharsetProvider.this) {
                        return lookup(csn);
                    }
                }

                public void remove() {
                    throw new UnsupportedOperationException();
                }
            };
    }

    public final String[] aliases(String charsetName) {
        synchronized (this) {
            init();
            return aliasNameMap.get(charsetName);
        }
    }

}