001/*
002 * ====================================================================
003 * Licensed to the Apache Software Foundation (ASF) under one
004 * or more contributor license agreements.  See the NOTICE file
005 * distributed with this work for additional information
006 * regarding copyright ownership.  The ASF licenses this file
007 * to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance
009 * with the License.  You may obtain a copy of the License at
010 *
011 *   http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing,
014 * software distributed under the License is distributed on an
015 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
016 * KIND, either express or implied.  See the License for the
017 * specific language governing permissions and limitations
018 * under the License.
019 * ====================================================================
020 *
021 * This software consists of voluntary contributions made by many
022 * individuals on behalf of the Apache Software Foundation.  For more
023 * information on the Apache Software Foundation, please see
024 * <http://www.apache.org/>.
025 *
026 */
027
028package org.apache.http.protocol;
029
030import java.util.Collection;
031import java.util.HashMap;
032import java.util.LinkedList;
033import java.util.Map;
034
035/**
036 * Builder class to build a linked list (chain) of unique class instances. Each class can have
037 * only one instance in the list. Useful for building lists of protocol interceptors.
038 *
039 * @see ImmutableHttpProcessor
040 *
041 * @since 4.3
042 */
043final class ChainBuilder<E> {
044
045    private final LinkedList<E> list;
046    private final Map<Class<?>, E> uniqueClasses;
047
048    public ChainBuilder() {
049        this.list = new LinkedList<E>();
050        this.uniqueClasses = new HashMap<Class<?>, E>();
051    }
052
053    private void ensureUnique(final E e) {
054        final E previous = this.uniqueClasses.remove(e.getClass());
055        if (previous != null) {
056            this.list.remove(previous);
057        }
058        this.uniqueClasses.put(e.getClass(), e);
059    }
060
061    public ChainBuilder<E> addFirst(final E e) {
062        if (e == null) {
063            return this;
064        }
065        ensureUnique(e);
066        this.list.addFirst(e);
067        return this;
068    }
069
070    public ChainBuilder<E> addLast(final E e) {
071        if (e == null) {
072            return this;
073        }
074        ensureUnique(e);
075        this.list.addLast(e);
076        return this;
077    }
078
079    public ChainBuilder<E> addAllFirst(final Collection<E> c) {
080        if (c == null) {
081            return this;
082        }
083        for (final E e: c) {
084            addFirst(e);
085        }
086        return this;
087    }
088
089    public ChainBuilder<E> addAllFirst(final E... c) {
090        if (c == null) {
091            return this;
092        }
093        for (final E e: c) {
094            addFirst(e);
095        }
096        return this;
097    }
098
099    public ChainBuilder<E> addAllLast(final Collection<E> c) {
100        if (c == null) {
101            return this;
102        }
103        for (final E e: c) {
104            addLast(e);
105        }
106        return this;
107    }
108
109    public ChainBuilder<E> addAllLast(final E... c) {
110        if (c == null) {
111            return this;
112        }
113        for (final E e: c) {
114            addLast(e);
115        }
116        return this;
117    }
118
119    public LinkedList<E> build() {
120        return new LinkedList<E>(this.list);
121    }
122
123}