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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 static final UnsafeValue EMPTY_UNSAFE = new UnsafeValue() {
@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 an empty {@link UnsafeValue value provider} whose {@link UnsafeValue#get() get()}
* method always returns {@code null}.
*
* @param value type.
* @return empty unsafe value provider.
*/
public static UnsafeValue emptyUnsafe() {
//noinspection unchecked
return (UnsafeValue) 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.
*
* 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 constant {@link UnsafeValue value provider} whose {@link UnsafeValue#get() get()}
* method always returns the instance supplied to the {@code value} parameter.
*
* In case the supplied value constant is {@code null}, an {@link #emptyUnsafe() empty} value
* provider is returned.
*
* @param value type.
* @param value value instance to be provided.
* @return constant value provider.
*/
public static UnsafeValue unsafe(final T value) {
return (value == null) ? Values.emptyUnsafe() : new InstanceUnsafeValue(value);
}
private static class InstanceUnsafeValue implements UnsafeValue {
private final T value;
public InstanceUnsafeValue(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(((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.
*
* In case the supplied throwable is {@code null}, an {@link NullPointerException} is thrown.
*
* @param value type.
* @param 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 UnsafeValue throwing(final E throwable) throws NullPointerException {
if (throwable == null) {
throw new NullPointerException("Supplied throwable ");
}
return new ExceptionValue(throwable);
}
private static class ExceptionValue implements UnsafeValue {
private final E throwable;
public ExceptionValue(final E throwable) {
this.throwable = throwable;
}
@Override
public T get() throws E {
throw throwable;
}
@Override
public boolean equals(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}.
*
* 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);
}
/**
* Get a new eagerly initialized {@link Value value provider}.
*
* 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.
*
* 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.
*
*
* 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 eagerly initialize the value provider.
* @return eagerly initialized, constant value provider.
*/
public static Value eager(final Value delegate) {
return (delegate == null) ? Values.empty() : new EagerValue(delegate);
}
private static class EagerValue implements Value {
private final T result;
private EagerValue(Value value) {
this.result = value.get();
}
@Override
public T get() {
return result;
}
}
private static class LazyValue implements Value {
private final Object lock;
private final Value delegate;
private volatile Value value;
public LazyValue(final Value delegate) {
this.delegate = delegate;
this.lock = new Object();
}
@Override
public T get() {
Value result = value;
if (result == null) {
synchronized (lock) {
result = value;
if (result == null) {
value = result = Values.of(delegate.get());
}
}
}
return result.get();
}
@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() + '}';
}
}
/**
* Get a new lazily initialized {@link UnsafeValue unsafe value provider}.
*
* 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.
*
* In case the call to underlying {@code delegate.get()} throws a throwable, the throwable is cached
* and thrown on all subsequent retrievals.
*
*
* 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 UnsafeValue lazy(final UnsafeValue delegate) {
return (delegate == null) ? Values.emptyUnsafe() : new LazyUnsafeValue(delegate);
}
private static class LazyUnsafeValue implements UnsafeValue {
private final Object lock;
private final UnsafeValue delegate;
private volatile UnsafeValue value;
public LazyUnsafeValue(final UnsafeValue delegate) {
this.delegate = delegate;
this.lock = new Object();
}
@Override
public T get() throws E {
UnsafeValue result = value;
if (result == null) {
synchronized (lock) {
result = value;
//noinspection ConstantConditions
if (result == null) {
try {
result = Values.unsafe(delegate.get());
} catch (Throwable e) {
//noinspection unchecked
result = Values.throwing((E) e);
}
value = result;
}
}
}
return result.get();
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
return delegate.equals(((LazyUnsafeValue) o).delegate);
}
@Override
public int hashCode() {
return delegate != null ? delegate.hashCode() : 0;
}
@Override
public String toString() {
return "LazyValue{delegate=" + delegate.toString() + '}';
}
}
}