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Lazy.java
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Lazy.java
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/*
* Copyright OmniFaces
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
* an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*/
package org.omnifaces.util;
import java.io.Serializable;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Supplier;
/**
* Implements lazy-initialized object primarily for final and transient fields.
* Utilizes double-checked locking for optimization.
* <p>
* Example:
* <pre>
* {@code
* private final Lazy<Object> lazy = new Lazy<>(Object::new);
* Object lazyInstance = lazy.get();
* }
* </pre>
* <p>
* <a href="https://github.com/flowlogix/flowlogix/blob/main/jakarta-ee/jee-examples/src/main/java/com/flowlogix/examples/LazyExample.java" target="_blank">Example Code (GitHub)</a>
*
* @param <T> Type of object.
* @author Lenny Primak
* @since 3.9
*/
public final class Lazy<T> implements Serializable {
private static final long serialVersionUID = 1L;
private transient T delegate;
private transient volatile boolean initialized;
private final Supplier<T> initFunction;
private final Lock lock = new ReentrantLock();
public interface SerializableSupplier<T> extends Supplier<T>, Serializable { }
public Lazy(SerializableSupplier<T> initFunction) {
this.initFunction = initFunction;
}
/**
* @return Underlying object, initialize when necessary.
*/
public T get() {
boolean localInitialized = this.initialized;
if (!localInitialized) {
lock.lock();
try {
if (!initialized) {
delegate = initFunction.get();
}
initialized = true;
}
finally {
lock.unlock();
}
}
return delegate;
}
}