src/com/facebook/buck/util/Types.java

/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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.facebook.buck.util;

import com.google.common.base.Optional;
import com.google.common.primitives.Primitives;

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;
import java.util.Collection;

import javax.annotation.Nullable;

public class Types {

  private Types() {
    // Utility class.
  }

  /**
   * Determine the "base type" of a field. That is, the following will be returned:
   * <ul>
   *   <li>{@code String} -> {@code String.class}
   *   <li>{@code Optional&lt;String>} -> {@code String.class}
   *   <li>{@code Set&lt;String>} -> {@code String.class}
   *   <li>{@code Collection&lt;? extends Comparable>} -> {@code Comparable.class}
   *   <li>{@code Collection&lt;? super Comparable} -> {@code Object.class}
   * </ul>
   */
  public static Type getBaseType(Field field) {
    Type type = getFirstNonOptionalType(field);

    if (type instanceof ParameterizedType) {
      type = ((ParameterizedType) type).getActualTypeArguments()[0];
    }

    if (type instanceof WildcardType) {
      type = ((WildcardType) type).getUpperBounds()[0];
    }

    return Primitives.wrap((Class<?>) type);
  }

  /**
   * @return The raw type of the {@link Collection} a field represents, even if contained in an
   *    {@link Optional}, but without the ParameterizedType information.
   */
  @SuppressWarnings("unchecked")
  @Nullable
  public static Class<? extends Collection<?>> getContainerClass(Field field) {
    Type type = getFirstNonOptionalType(field);

    if (!(type instanceof ParameterizedType)) {
      return null;
    }

    Type rawType = ((ParameterizedType) type).getRawType();
    if (!(rawType instanceof Class)) {
      return null;
    }

    Class<?> clazz = (Class<?>) rawType;
    if (!(Collection.class.isAssignableFrom(clazz))) {
      return null;
    }

    return (Class<? extends Collection<?>>) clazz;
  }

  /**
   * Get the first complete {@link Type} in a signature that's non-optional, complete with the
   * information from the {@link ParameterizedType}.
   *
   * <ul>
   *   <li>String -> String
   *   <li>Optional&lt;String> -> String
   *   <li>ImmutableSet&lt;String> -> ImmutableSet&lt;String>
   *   <li>Optional&lt;ImmutableSet&lt;String>> -> ImmutableSet&lt;String>
   * </ul>
   */
  public static Type getFirstNonOptionalType(Field field) {
    boolean isOptional = Optional.class.isAssignableFrom(field.getType());
    if (isOptional) {
      Type type = field.getGenericType();

      if (type instanceof ParameterizedType) {
        return ((ParameterizedType) type).getActualTypeArguments()[0];
      } else {
        throw new RuntimeException("Unexpected type parameter for Optional: " + type);
      }
    } else {
      return field.getGenericType();
    }
  }
}