001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.camel.util;
018
019import java.lang.ref.WeakReference;
020import java.util.function.Supplier;
021
022public final class WeakThreadLocal<T> implements Supplier<T> {
023    private final ThreadLocal<WeakReference<T>> cache;
024    private final Supplier<T> supplier;
025
026    public WeakThreadLocal(Supplier<T> supplier) {
027        this.cache = new ThreadLocal<>();
028        this.supplier = ObjectHelper.notNull(supplier, "value supplier");
029    }
030
031    @Override
032    public T get() {
033        T value = null;
034        WeakReference<T> ref = cache.get();
035
036        if (ref != null) {
037            value = ref.get();
038        }
039
040        if (value == null) {
041            value = supplier.get();
042            cache.set(new WeakReference<>(value));
043        }
044
045        return value;
046    }
047
048    public static <T> WeakThreadLocal<T> withSupplier(Supplier<T> supplier) {
049        return new WeakThreadLocal<>(supplier);
050    }
051}