jetty-util/src/main/java/org/eclipse/jetty/util/AttributesMap.java

//
//  ========================================================================
//  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.util;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicReference;

public class AttributesMap implements Attributes
{
    private final AtomicReference<ConcurrentMap<String, Object>> _map = new AtomicReference<>();

    public AttributesMap()
    {
    }

    public AttributesMap(AttributesMap attributes)
    {
        ConcurrentMap<String, Object> map = attributes.map();
        if (map != null)
            _map.set(new ConcurrentHashMap<>(map));
    }

    private ConcurrentMap<String, Object> map()
    {
        return _map.get();
    }

    private ConcurrentMap<String, Object> ensureMap()
    {
        while (true)
        {
            ConcurrentMap<String, Object> map = map();
            if (map != null)
                return map;
            map = new ConcurrentHashMap<>();
            if (_map.compareAndSet(null, map))
                return map;
        }
    }

    @Override
    public void removeAttribute(String name)
    {
        Map<String, Object> map = map();
        if (map != null)
            map.remove(name);
    }

    @Override
    public void setAttribute(String name, Object attribute)
    {
        if (attribute == null)
            removeAttribute(name);
        else
            ensureMap().put(name, attribute);
    }

    @Override
    public Object getAttribute(String name)
    {
        Map<String, Object> map = map();
        return map == null ? null : map.get(name);
    }

    @Override
    public Enumeration<String> getAttributeNames()
    {
        return Collections.enumeration(getAttributeNameSet());
    }

    public Set<String> getAttributeNameSet()
    {
        return keySet();
    }

    public Set<Map.Entry<String, Object>> getAttributeEntrySet()
    {
        Map<String, Object> map = map();
        return map == null ? Collections.<Map.Entry<String, Object>>emptySet() : map.entrySet();
    }

    public static Enumeration<String> getAttributeNamesCopy(Attributes attrs)
    {
        if (attrs instanceof AttributesMap)
            return Collections.enumeration(((AttributesMap)attrs).keySet());

        List<String> names = new ArrayList<>();
        names.addAll(Collections.list(attrs.getAttributeNames()));
        return Collections.enumeration(names);
    }

    @Override
    public void clearAttributes()
    {
        Map<String, Object> map = map();
        if (map != null)
            map.clear();
    }

    public int size()
    {
        Map<String, Object> map = map();
        return map == null ? 0 : map.size();
    }

    @Override
    public String toString()
    {
        Map<String, Object> map = map();
        return map == null ? "{}" : map.toString();
    }

    private Set<String> keySet()
    {
        Map<String, Object> map = map();
        return map == null ? Collections.<String>emptySet() : map.keySet();
    }

    public void addAll(Attributes attributes)
    {
        Enumeration<String> e = attributes.getAttributeNames();
        while (e.hasMoreElements())
        {
            String name = e.nextElement();
            setAttribute(name, attributes.getAttribute(name));
        }
    }
}