org.glassfish.jersey.internal.util.collection.Values Maven / Gradle / Ivy
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright (c) 2012 Oracle and/or its affiliates. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common Development
* and Distribution License("CDDL") (collectively, the "License"). You
* may not use this file except in compliance with the License. You can
* obtain a copy of the License at
* http://glassfish.java.net/public/CDDL+GPL_1_1.html
* or packager/legal/LICENSE.txt. See the License for the specific
* language governing permissions and limitations under the License.
*
* When distributing the software, include this License Header Notice in each
* file and include the License file at packager/legal/LICENSE.txt.
*
* GPL Classpath Exception:
* Oracle designates this particular file as subject to the "Classpath"
* exception as provided by Oracle in the GPL Version 2 section of the License
* file that accompanied this code.
*
* Modifications:
* If applicable, add the following below the License Header, with the fields
* enclosed by brackets [] replaced by your own identifying information:
* "Portions Copyright [year] [name of copyright owner]"
*
* Contributor(s):
* If you wish your version of this file to be governed by only the CDDL or
* only the GPL Version 2, indicate your decision by adding "[Contributor]
* elects to include this software in this distribution under the [CDDL or GPL
* Version 2] license." If you don't indicate a single choice of license, a
* recipient has the option to distribute your version of this file under
* either the CDDL, the GPL Version 2 or to extend the choice of license to
* its licensees as provided above. However, if you add GPL Version 2 code
* and therefore, elected the GPL Version 2 license, then the option applies
* only if the new code is made subject to such option by the copyright
* holder.
*/
package org.glassfish.jersey.internal.util.collection;
/**
* A collection of {@link Value Value provider} factory & utility methods.
*
* @author Marek Potociar (marek.potociar at oracle.com)
*/
public final class Values {
private static final Value EMPTY = new Value() {
@Override
public Object get() {
return null;
}
};
private Values() {
// prevents instantiation.
}
/**
* Get an empty {@link Value value provider} whose {@link Value#get() get()}
* method always returns {@code null}.
*
* @param value type.
* @return empty value provider.
*/
public static Value empty() {
//noinspection unchecked
return (Value) EMPTY;
}
/**
* Get a new constant {@link Value value provider} whose {@link Value#get() get()}
* method always returns the instance supplied to the {@code value} parameter.
*
* In case the supplied value constant is {@code null}, an {@link #empty() empty} value
* provider is returned.
*
* @param value type.
* @param value value instance to be provided.
* @return constant value provider.
*/
public static Value of(final T value) {
return (value == null) ? Values.empty() : new InstanceValue(value);
}
private static class InstanceValue implements Value {
private final T value;
public InstanceValue(final T value) {
this.value = value;
}
@Override
public T get() {
return value;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
return value.equals(((InstanceValue) o).value);
}
@Override
public int hashCode() {
return value != null ? value.hashCode() : 0;
}
@Override
public String toString() {
return "InstanceValue{value=" + value + '}';
}
}
/**
* Get a new lazily initialized {@link Value value provider}.
*
* The value returned by its {@link Value#get() get()} method is lazily retrieved during a first
* call to the method from the supplied {@code delegate} value provider and is then cached for
* a subsequent retrieval.
*
* The implementation of the returned lazy value provider is thread-safe and is guaranteed to
* invoke the {@code get()} method on the supplied {@code delegate} value provider instance at
* most once.
*
*
* If the supplied value provider is {@code null}, an {@link #empty() empty} value
* provider is returned.
*
*
* @param value type.
* @param delegate value provider delegate that will be used to lazily initialize the value provider.
* @return lazily initialized value provider.
*/
public static Value lazy(final Value delegate) {
return (delegate == null) ? Values.empty() : new LazyValue(delegate);
}
private static class LazyValue implements Value {
private final Object lock;
private final Value delegate;
private volatile T value;
public LazyValue(final Value delegate) {
this.delegate = delegate;
this.lock = new Object();
}
@Override
public T get() {
T result = value;
if (result == null) {
synchronized (lock) {
result = value;
//noinspection ConstantConditions
if (result == null) {
value = result = delegate.get();
}
}
}
return result;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
return delegate.equals(((LazyValue) o).delegate);
}
@Override
public int hashCode() {
return delegate != null ? delegate.hashCode() : 0;
}
@Override
public String toString() {
return "LazyValue{delegate=" + delegate.toString() + '}';
}
}
}