Values.java
/*
* Copyright (c) 2012, 2019 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package org.glassfish.jersey.internal.util.collection;
/**
* A collection of {@link Value Value provider} factory & utility methods.
*
* @author Marek Potociar
*/
public final class Values {
private static final LazyValue EMPTY = new LazyValue() {
@Override
public Object get() {
return null;
}
@Override
public boolean isInitialized() {
return true;
}
};
private static final LazyUnsafeValue EMPTY_UNSAFE = new LazyUnsafeValue() {
@Override
public Object get() {
return null;
}
@Override
public boolean isInitialized() {
return true;
}
};
private Values() {
// prevents instantiation.
}
/**
* Get an empty {@link Value value provider} whose {@link Value#get() get()}
* method always returns {@code null}.
*
* @param <T> value type.
* @return empty value provider.
*/
public static <T> Value<T> empty() {
//noinspection unchecked
return (Value<T>) EMPTY;
}
/**
* Get an empty {@link UnsafeValue value provider} whose {@link UnsafeValue#get() get()}
* method always returns {@code null}.
*
* @param <T> value type.
* @return empty unsafe value provider.
*/
public static <T, E extends Throwable> UnsafeValue<T, E> emptyUnsafe() {
//noinspection unchecked
return (UnsafeValue<T, E>) EMPTY_UNSAFE;
}
/**
* Get a new constant {@link Value value provider} whose {@link Value#get() get()}
* method always returns the instance supplied to the {@code value} parameter.
* <p/>
* In case the supplied value constant is {@code null}, an {@link #empty() empty} value
* provider is returned.
*
* @param <T> value type.
* @param value value instance to be provided.
* @return constant value provider.
*/
public static <T> Value<T> of(final T value) {
return (value == null) ? Values.<T>empty() : new InstanceValue<T>(value);
}
private static class InstanceValue<T> implements Value<T> {
private final T value;
public InstanceValue(final T value) {
this.value = value;
}
@Override
public T get() {
return value;
}
@Override
public boolean equals(final 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 constant {@link UnsafeValue value provider} whose {@link UnsafeValue#get() get()}
* method always returns the instance supplied to the {@code value} parameter.
* <p/>
* In case the supplied value constant is {@code null}, an {@link #emptyUnsafe() empty} value
* provider is returned.
*
* @param <T> value type.
* @param value value instance to be provided.
* @return constant value provider.
*/
public static <T, E extends Throwable> UnsafeValue<T, E> unsafe(final T value) {
return (value == null) ? Values.<T, E>emptyUnsafe() : new InstanceUnsafeValue<T, E>(value);
}
private static class InstanceUnsafeValue<T, E extends Throwable> implements UnsafeValue<T, E> {
private final T value;
public InstanceUnsafeValue(final T value) {
this.value = value;
}
@Override
public T get() {
return value;
}
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
return value.equals(((InstanceUnsafeValue) o).value);
}
@Override
public int hashCode() {
return value != null ? value.hashCode() : 0;
}
@Override
public String toString() {
return "InstanceUnsafeValue{value=" + value + '}';
}
}
/**
* Get a new "throwing" {@link UnsafeValue unsafe value provider} whose {@link UnsafeValue#get() get()}
* method always throws the exception supplied to the {@code throwable} parameter.
* <p/>
* In case the supplied throwable is {@code null}, an {@link NullPointerException} is thrown.
*
* @param <T> value type.
* @param <E> exception type.
* @param throwable throwable instance to be thrown.
* @return "throwing" unsafe value provider.
* @throws NullPointerException in case the supplied throwable instance is {@code null}.
*/
public static <T, E extends Throwable> UnsafeValue<T, E> throwing(final E throwable) {
if (throwable == null) {
throw new NullPointerException("Supplied throwable ");
}
return new ExceptionValue<T, E>(throwable);
}
private static class ExceptionValue<T, E extends Throwable> implements UnsafeValue<T, E> {
private final E throwable;
public ExceptionValue(final E throwable) {
this.throwable = throwable;
}
@Override
public T get() throws E {
throw throwable;
}
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
return throwable.equals(((ExceptionValue) o).throwable);
}
@Override
public int hashCode() {
return throwable != null ? throwable.hashCode() : 0;
}
@Override
public String toString() {
return "ExceptionValue{throwable=" + throwable + '}';
}
}
/**
* Get a new lazily initialized {@link Value value provider}.
* <p/>
* 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.
* <p>
* 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.
* </p>
* <p>
* If the supplied value provider is {@code null}, an {@link #empty() empty} value
* provider is returned.
* </p>
*
* @param <T> value type.
* @param delegate value provider delegate that will be used to lazily initialize the value provider.
* @return lazily initialized value provider.
*/
public static <T> LazyValue<T> lazy(final Value<T> delegate) {
//noinspection unchecked
return (delegate == null) ? (LazyValue<T>) EMPTY : new LazyValueImpl<T>(delegate);
}
/**
* Get a new eagerly initialized {@link Value value provider}.
* <p/>
* The value returned by its {@link Value#get() get()} method is eagerly computed from the supplied
* {@code delegate} value provider and is then stored in a final field for a subsequent retrieval.
* <p>
* The implementation of the returned eager value provider is thread-safe and is guaranteed to
* invoke the {@code get()} method on the supplied {@code delegate} value provider instance once
* and only once.
* </p>
* <p>
* If the supplied value provider is {@code null}, an {@link #empty() empty} value
* provider is returned.
* </p>
*
* @param <T> value type.
* @param delegate value provider delegate that will be used to eagerly initialize the value provider.
* @return eagerly initialized, constant value provider.
*/
public static <T> Value<T> eager(final Value<T> delegate) {
return (delegate == null) ? Values.<T>empty() : new EagerValue<T>(delegate);
}
private static class EagerValue<T> implements Value<T> {
private final T result;
private EagerValue(final Value<T> value) {
this.result = value.get();
}
@Override
public T get() {
return result;
}
}
private static class LazyValueImpl<T> implements LazyValue<T> {
private final Object lock;
private final Value<T> delegate;
private volatile Value<T> value;
public LazyValueImpl(final Value<T> delegate) {
this.delegate = delegate;
this.lock = new Object();
}
@Override
public T get() {
Value<T> result = value;
if (result == null) {
synchronized (lock) {
result = value;
if (result == null) {
value = result = Values.of(delegate.get());
}
}
}
return result.get();
}
@Override
public boolean isInitialized() {
return value != null;
}
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
return delegate.equals(((LazyValueImpl) o).delegate);
}
@Override
public int hashCode() {
return delegate != null ? delegate.hashCode() : 0;
}
@Override
public String toString() {
return "LazyValue{delegate=" + delegate.toString() + '}';
}
}
/**
* Get a new lazily initialized {@link UnsafeValue unsafe value provider}.
* <p/>
* The value returned by its {@link UnsafeValue#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.
* <p>
* In case the call to underlying {@code delegate.get()} throws a throwable, the throwable is cached
* and thrown on all subsequent retrievals.
* </p>
* <p>
* 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.
* </p>
* <p>
* If the supplied value provider is {@code null}, an {@link #empty() empty} value
* provider is returned.
* </p>
*
* @param <T> value type.
* @param delegate value provider delegate that will be used to lazily initialize the value provider.
* @return lazily initialized value provider.
*/
public static <T, E extends Throwable> LazyUnsafeValue<T, E> lazy(final UnsafeValue<T, E> delegate) {
//noinspection unchecked
return (delegate == null) ? (LazyUnsafeValue<T, E>) EMPTY_UNSAFE : new LazyUnsafeValueImpl<T, E>(delegate);
}
private static class LazyUnsafeValueImpl<T, E extends Throwable> implements LazyUnsafeValue<T, E> {
private final Object lock;
private final UnsafeValue<T, E> delegate;
private volatile UnsafeValue<T, E> value;
public LazyUnsafeValueImpl(final UnsafeValue<T, E> delegate) {
this.delegate = delegate;
this.lock = new Object();
}
@Override
public T get() throws E {
UnsafeValue<T, E> result = value;
if (result == null) {
synchronized (lock) {
result = value;
//noinspection ConstantConditions
if (result == null) {
try {
result = Values.unsafe(delegate.get());
} catch (final Throwable e) {
//noinspection unchecked
result = Values.throwing((E) e);
}
value = result;
}
}
}
return result.get();
}
@Override
public boolean isInitialized() {
return value != null;
}
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
return delegate.equals(((LazyUnsafeValueImpl) o).delegate);
}
@Override
public int hashCode() {
return delegate != null ? delegate.hashCode() : 0;
}
@Override
public String toString() {
return "LazyValue{delegate=" + delegate.toString() + '}';
}
}
}