com.uber.hoodie.common.util.Option Maven / Gradle / Ivy

Go to download
/*
 *  Copyright (c) 2016 Uber Technologies, Inc. ([email protected])
 *
 *  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
 *
 *           http://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 com.uber.hoodie.common.util;

import java.io.Serializable;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;

/**
 * Copied from java.util.Optional and made Serializable along with methods to convert to/from standard Option
 */
public final class Option implements Serializable {

  private static final long serialVersionUID = 0L;

  /**
   * Common instance for {@code empty()}.
   */
  private static final Option EMPTY = new Option<>();

  /**
   * If non-null, the value; if null, indicates no value is present
   */
  private final T value;

  /**
   * Constructs an empty instance.
   *
   * @implNote Generally only one empty instance, {@link Option#EMPTY}, should exist per VM.
   */
  private Option() {
    this.value = null;
  }

  /**
   * Returns an empty {@code Option} instance.  No value is present for this Option.
   *
   * @param  Type of the non-existent value
   * @return an empty {@code Option}
   * @apiNote Though it may be tempting to do so, avoid testing if an object is empty by comparing with {@code ==}
   * against instances returned by {@code Option.empty()}. There is no guarantee that it is a singleton. Instead, use
   * {@link #isPresent()}.
   */
  public static  Option empty() {
    @SuppressWarnings("unchecked")
    Option t = (Option) EMPTY;
    return t;
  }

  /**
   * Constructs an instance with the value present.
   *
   * @param value the non-null value to be present
   * @throws NullPointerException if value is null
   */
  private Option(T value) {
    this.value = Objects.requireNonNull(value);
  }

  /**
   * Returns an {@code Option} with the specified present non-null value.
   *
   * @param  the class of the value
   * @param value the value to be present, which must be non-null
   * @return an {@code Option} with the value present
   * @throws NullPointerException if value is null
   */
  public static  Option of(T value) {
    return new Option<>(value);
  }

  /**
   * Returns an {@code Option} describing the specified value, if non-null, otherwise returns an empty {@code Option}.
   *
   * @param  the class of the value
   * @param value the possibly-null value to describe
   * @return an {@code Option} with a present value if the specified value is non-null, otherwise an empty {@code
   * Option}
   */
  public static  Option ofNullable(T value) {
    return value == null ? empty() : of(value);
  }

  /**
   * If a value is present in this {@code Option}, returns the value, otherwise throws {@code NoSuchElementException}.
   *
   * @return the non-null value held by this {@code Option}
   * @throws NoSuchElementException if there is no value present
   * @see Option#isPresent()
   */
  public T get() {
    if (value == null) {
      throw new NoSuchElementException("No value present");
    }
    return value;
  }

  /**
   * Return {@code true} if there is a value present, otherwise {@code false}.
   *
   * @return {@code true} if there is a value present, otherwise {@code false}
   */
  public boolean isPresent() {
    return value != null;
  }

  /**
   * If a value is present, invoke the specified consumer with the value, otherwise do nothing.
   *
   * @param consumer block to be executed if a value is present
   * @throws NullPointerException if value is present and {@code consumer} is null
   */
  public void ifPresent(Consumer consumer) {
    if (value != null) {
      consumer.accept(value);
    }
  }

  /**
   * If a value is present, and the value matches the given predicate, return an {@code Option} describing the value,
   * otherwise return an empty {@code Option}.
   *
   * @param predicate a predicate to apply to the value, if present
   * @return an {@code Option} describing the value of this {@code Option} if a value is present and the value matches
   * the given predicate, otherwise an empty {@code Option}
   * @throws NullPointerException if the predicate is null
   */
  public Option filter(Predicate predicate) {
    Objects.requireNonNull(predicate);
    if (!isPresent()) {
      return this;
    } else {
      return predicate.test(value) ? this : empty();
    }
  }

  /**
   * If a value is present, apply the provided mapping function to it, and if the result is non-null, return an {@code
   * Option} describing the result.  Otherwise return an empty {@code Option}.
   *
   * @param  The type of the result of the mapping function
   * @param mapper a mapping function to apply to the value, if present
   * @return an {@code Option} describing the result of applying a mapping function to the value of this {@code Option},
   * if a value is present, otherwise an empty {@code Option}
   * @throws NullPointerException if the mapping function is null
   * @apiNote This method supports post-processing on optional values, without the need to explicitly check for a return
   * status.  For example, the following code traverses a stream of file names, selects one that has not yet been
   * processed, and then opens that file, returning an {@code Option}:
   *
   * {@code
   *     Option fis =
   *         names.stream().filter(name -> !isProcessedYet(name))
   *                       .findFirst()
   *                       .map(name -> new FileInputStream(name));
   * }
   *
   * Here, {@code findFirst} returns an {@code Option}, and then {@code map} returns an {@code
   * Option} for the desired file if one exists.
   */
  public  Option map(Function mapper) {
    Objects.requireNonNull(mapper);
    if (!isPresent()) {
      return empty();
    } else {
      return Option.ofNullable(mapper.apply(value));
    }
  }

  /**
   * If a value is present, apply the provided {@code Option}-bearing mapping function to it, return that result,
   * otherwise return an empty {@code Option}.  This method is similar to {@link #map(Function)}, but the provided
   * mapper is one whose result is already an {@code Option}, and if invoked, {@code flatMap} does not wrap it with an
   * additional {@code Option}.
   *
   * @param  The type parameter to the {@code Option} returned by
   * @param mapper a mapping function to apply to the value, if present the mapping function
   * @return the result of applying an {@code Option}-bearing mapping function to the value of this {@code Option}, if a
   * value is present, otherwise an empty {@code Option}
   * @throws NullPointerException if the mapping function is null or returns a null result
   */
  public  Option flatMap(Function> mapper) {
    Objects.requireNonNull(mapper);
    if (!isPresent()) {
      return empty();
    } else {
      return Objects.requireNonNull(mapper.apply(value));
    }
  }

  /**
   * Return the value if present, otherwise return {@code other}.
   *
   * @param other the value to be returned if there is no value present, may be null
   * @return the value, if present, otherwise {@code other}
   */
  public T orElse(T other) {
    return value != null ? value : other;
  }

  /**
   * Return the value if present, otherwise invoke {@code other} and return the result of that invocation.
   *
   * @param other a {@code Supplier} whose result is returned if no value is present
   * @return the value if present otherwise the result of {@code other.get()}
   * @throws NullPointerException if value is not present and {@code other} is null
   */
  public T orElseGet(Supplier other) {
    return value != null ? value : other.get();
  }

  /**
   * Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
   *
   * @param  Type of the exception to be thrown
   * @param exceptionSupplier The supplier which will return the exception to be thrown
   * @return the present value
   * @throws X if there is no value present
   * @throws NullPointerException if no value is present and {@code exceptionSupplier} is null
   * @apiNote A method reference to the exception constructor with an empty argument list can be used as the supplier.
   * For example, {@code IllegalStateException::new}
   */
  public  T orElseThrow(Supplier exceptionSupplier) throws X {
    if (value != null) {
      return value;
    } else {
      throw exceptionSupplier.get();
    }
  }

  /**
   * Indicates whether some other object is "equal to" this Option. The other object is considered equal if:
   * 
   * it is also an {@code Option} and;
   * 
both instances have no value present or;
   * 
the present values are "equal to" each other via {@code equals()}.
   * 
   *
   * @param obj an object to be tested for equality
   * @return {code true} if the other object is "equal to" this object otherwise {@code false}
   */
  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }

    if (!(obj instanceof Option)) {
      return false;
    }

    Option other = (Option) obj;
    return Objects.equals(value, other.value);
  }

  /**
   * Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
   *
   * @return hash code value of the present value or 0 if no value is present
   */
  @Override
  public int hashCode() {
    return Objects.hashCode(value);
  }

  /**
   * Returns a non-empty string representation of this Option suitable for debugging. The exact presentation format is
   * unspecified and may vary between implementations and versions.
   *
   * @return the string representation of this instance
   * @implSpec If a value is present the result must include its string representation in the result. Empty and present
   * Optionals must be unambiguously differentiable.
   */
  @Override
  public String toString() {
    return value != null
        ? String.format("Option[%s]", value)
        : "Option.empty";
  }

  /**
   * Convert to java Optional
   */
  public Optional toJavaOptional() {
    return Optional.ofNullable(value);
  }

  /**
   * Convert from java.util.Optional
   */
  public static  Option fromJavaOptional(Optional v) {
    return Option.ofNullable(v.orElse(null));
  }
}