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This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * 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.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Equivalence;
import com.google.common.base.Function;
import com.google.common.collect.MapMakerInternalMap.ReferenceEntry;

import java.util.concurrent.ConcurrentMap;

/**
 * Contains static methods pertaining to instances of {@link Interner}.
 *
 * @author Kevin Bourrillion
 * @since 3.0
 */
@Beta
public final class Interners {
  private Interners() {}

  /**
   * Returns a new thread-safe interner which retains a strong reference to each instance it has
   * interned, thus preventing these instances from being garbage-collected. If this retention is
   * acceptable, this implementation may perform better than {@link #newWeakInterner}. Note that
   * unlike {@link String#intern}, using this interner does not consume memory in the permanent
   * generation.
   */
  public static  Interner newStrongInterner() {
    final ConcurrentMap map = new MapMaker().makeMap();
    return new Interner() {
      @Override public E intern(E sample) {
        E canonical = map.putIfAbsent(checkNotNull(sample), sample);
        return (canonical == null) ? sample : canonical;
      }
    };
  }

  /**
   * Returns a new thread-safe interner which retains a weak reference to each instance it has
   * interned, and so does not prevent these instances from being garbage-collected. This most
   * likely does not perform as well as {@link #newStrongInterner}, but is the best alternative
   * when the memory usage of that implementation is unacceptable. Note that unlike {@link
   * String#intern}, using this interner does not consume memory in the permanent generation.
   */
  @GwtIncompatible("java.lang.ref.WeakReference")
  public static  Interner newWeakInterner() {
    return new WeakInterner();
  }

  private static class WeakInterner implements Interner {
    // MapMaker is our friend, we know about this type
    private final MapMakerInternalMap map = new MapMaker()
          .weakKeys()
          .keyEquivalence(Equivalence.equals())
          .makeCustomMap();

    @Override public E intern(E sample) {
      while (true) {
        // trying to read the canonical...
        ReferenceEntry entry = map.getEntry(sample);
        if (entry != null) {
          E canonical = entry.getKey();
          if (canonical != null) { // only matters if weak/soft keys are used
            return canonical;
          }
        }

        // didn't see it, trying to put it instead...
        Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
        if (sneaky == null) {
          return sample;
        } else {
          /* Someone beat us to it! Trying again...
           *
           * Technically this loop not guaranteed to terminate, so theoretically (extremely
           * unlikely) this thread might starve, but even then, there is always going to be another
           * thread doing progress here.
           */
        }
      }
    }

    private enum Dummy { VALUE }
  }

  /**
   * Returns a function that delegates to the {@link Interner#intern} method of the given interner.
   *
   * @since 8.0
   */
  public static  Function asFunction(Interner interner) {
    return new InternerFunction(checkNotNull(interner));
  }

  private static class InternerFunction implements Function {

    private final Interner interner;

    public InternerFunction(Interner interner) {
      this.interner = interner;
    }

    @Override public E apply(E input) {
      return interner.intern(input);
    }

    @Override public int hashCode() {
      return interner.hashCode();
    }

    @Override public boolean equals(Object other) {
      if (other instanceof InternerFunction) {
        InternerFunction that = (InternerFunction) other;
        return interner.equals(that.interner);
      }

      return false;
    }
  }
}