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Java 1.8+ Library with tons of utility classes required in all projects
There is a newer version: 11.1.10
/*
 * Copyright (C) 2014-2022 Philip Helger (www.helger.com)
 * philip[at]helger[dot]com
 *
 * 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.helger.commons.cache;

import java.lang.annotation.Annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.NotThreadSafe;

import com.helger.commons.ValueEnforcer;
import com.helger.commons.collection.impl.CommonsHashMap;
import com.helger.commons.collection.impl.ICommonsMap;
import com.helger.commons.state.ETriState;
import com.helger.commons.string.ToStringGenerator;

/**
 * A simple cache for the usage of a certain annotation class at other classes.
 * 

 * Note: cannot use {@link com.helger.commons.cache.Cache} because it would need
 * a Class<?> as a key and this would be a hard wired
 * reference.

 * Since 10.1.3 the class is no longer read-write-locked, as the performance
 * overhead is too big for reading only, compared to the penalty of double
 * annotation determination.
 *
 * @author Philip Helger
 */
@NotThreadSafe
public class AnnotationUsageCache
{
  private final Class  m_aAnnotationClass;
  private final ICommonsMap  m_aMap = new CommonsHashMap <> ();

  /**
   * Constructor
   *
   * @param aAnnotationClass
   *        The annotation class to store the existence of. It must have the
   *        {@link RetentionPolicy#RUNTIME} to be usable within this class!
   */
  public AnnotationUsageCache (@Nonnull final Class  aAnnotationClass)
  {
    ValueEnforcer.notNull (aAnnotationClass, "AnnotationClass");

    // Check retention policy
    final Retention aRetention = aAnnotationClass.getAnnotation (Retention.class);
    final RetentionPolicy eRetentionPolicy = aRetention == null ? RetentionPolicy.CLASS : aRetention.value ();
    if (eRetentionPolicy != RetentionPolicy.RUNTIME)
      throw new IllegalArgumentException ("RetentionPolicy must be of type RUNTIME to be used within this cache. The current value ist " +
                                          eRetentionPolicy);

    // Save to members
    m_aAnnotationClass = aAnnotationClass;
  }

  /**
   * @return The annotation class passed in the constructor. Never
   *         null.
   */
  @Nonnull
  public final Class  getAnnotationClass ()
  {
    return m_aAnnotationClass;
  }

  /**
   * Check if the class of the passed object has the annotation provided in the
   * constructor.
   *
   * @param aObject
   *        The object. To be checked. May not be null.
   * @return true if the owning class has the annotation,
   *         false if not.
   * @see #hasAnnotation(Class)
   */
  public boolean hasAnnotation (@Nonnull final Object aObject)
  {
    ValueEnforcer.notNull (aObject, "Object");

    return hasAnnotation (aObject.getClass ());
  }

  /**
   * Check if the provided class has the annotation from the constructor or not.
   * If the value is not yet in the cache, it will be determined.
   *
   * @param aClass
   *        The class to check. May not be null.
   * @return true if the provided class has the annotation,
   *         false if not.
   */
  public boolean hasAnnotation (@Nonnull final Class  aClass)
  {
    ValueEnforcer.notNull (aClass, "Class");

    final String sClassName = aClass.getName ();

    if (false)
    {
      // Don't use computeIfAbsent here, because it can throw
      // ConcurrentModificationException in Java 11
      return m_aMap.computeIfAbsent (sClassName, k -> ETriState.valueOf (aClass.getAnnotation (m_aAnnotationClass) != null)).isTrue ();
    }

    // This version is save for Java 1.8 and Java 11
    ETriState e = m_aMap.get (sClassName);
    if (e == null)
    {
      // Evtl. double retrieval is okay
      e = ETriState.valueOf (aClass.getAnnotation (m_aAnnotationClass) != null);
      m_aMap.put (sClassName, e);
    }
    return e.isTrue ();
  }

  /**
   * In case the knowledge was gathered on the outside, remember the wisdom in
   * this class.
   *
   * @param aClass
   *        The class that it is about.
   * @param bHasAnnotation
   *        true to indicate the presence, false to
   */
  public void setAnnotation (@Nonnull final Class  aClass, final boolean bHasAnnotation)
  {
    ValueEnforcer.notNull (aClass, "Class");

    final String sClassName = aClass.getName ();

    m_aMap.put (sClassName, ETriState.valueOf (bHasAnnotation));
  }

  /**
   * Remove all entries from the cache. That is mainly of interested for testing
   * purposes, to provide a clean state.
   */
  public void clearCache ()
  {
    m_aMap.clear ();
  }

  @Override
  public String toString ()
  {
    return new ToStringGenerator (this).append ("AnnotationClass", m_aAnnotationClass).append ("Map", m_aMap).getToString ();
  }
}