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}