content: /*
   * This library is part of OpenCms -
   * the Open Source Content Management System
   *
   * Copyright (c) Alkacon Software GmbH & Co. KG (https://www.alkacon.com)
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   * Lesser General Public License for more details.
   *
   * For further information about Alkacon Software, please see the
   * company website: https://www.alkacon.com
   *
   * For further information about OpenCms, please see the
   * project website: https://www.opencms.org
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  
  package org.opencms.util;
  
  import org.opencms.main.CmsLog;
  
  import java.util.Collection;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.commons.logging.Log;
  
  /**
   * Wrapper around ConcurrentHashMap which allows null values.<p>
   *
   * The point of this is the following: Often, HashMaps in older code are accessed concurrently by multiple threads. When these threads modify the
   * map concurrently, an infinite loop may occur due to the standard HashMap implementation. But sometimes we can't just replace the HashMap with a
   * ConcurrentHashMap because that class doesn't allow null values and we don't always know for certain whether null values are used or not.
   *
   * But if we don't care about the distinction about null values and entries not being present, we can use this map class which will just log an error
   * and remove the entry when trying to set a null value.
   *
   * NOTE: Currently this wrapper does *not* check value modifications made to entries returned by entrySet!
   *
   * @param <K> the key type
   * @param <V> the value type
   */
  public class CmsNullIgnoringConcurrentMap<K, V> implements Map<K, V> {
  
      /** The logger for this class. */
      private static final Log LOG = CmsLog.getLog(CmsNullIgnoringConcurrentMap.class);
  
      /** The wrapped map. */
      private Map<K, V> m_internalMap = new ConcurrentHashMap<K, V>();
  
      /**
       * Creates a new instance.<p>
       */
      public CmsNullIgnoringConcurrentMap() {
  
      }
  
      /**
       * Creates a new instance from another map.<p>
       *
       * @param otherMap the other map
       */
      public CmsNullIgnoringConcurrentMap(Map<K, V> otherMap) {
  
          for (Map.Entry<K, V> entry : otherMap.entrySet()) {
              put(entry.getKey(), entry.getValue());
          }
      }
  
      /**
       *
       * @see java.util.Map#clear()
       */
      public void clear() {
  
          m_internalMap.clear();
      }
  
      /**
       * @see java.util.Map#containsKey(java.lang.Object)
       */
      public boolean containsKey(Object key) {
  
          return m_internalMap.containsKey(key);
      }
  
      /**
       * @see java.util.Map#containsValue(java.lang.Object)
       */
      public boolean containsValue(Object value) {
  
          return m_internalMap.containsValue(value);
      }
  
      /**
       * @see java.util.Map#entrySet()
       */
      public Set<Map.Entry<K, V>> entrySet() {
  
          return m_internalMap.entrySet();
      }
  
      /**
       * @see java.util.Map#equals(java.lang.Object)
       */
      @Override
      public boolean equals(Object o) {
  
          return m_internalMap.equals(o);
      }
  
      /**
       * @see java.util.Map#get(java.lang.Object)
       */
      public V get(Object key) {
  
          return m_internalMap.get(key);
      }
  
      /**
       * @see java.util.Map#hashCode()
       */
      @Override
      public int hashCode() {
  
          return m_internalMap.hashCode();
      }
  
      /**
       * @see java.util.Map#isEmpty()
       */
      public boolean isEmpty() {
  
          return m_internalMap.isEmpty();
      }
  
      /**
       * @see java.util.Map#keySet()
       */
      public Set<K> keySet() {
  
          return m_internalMap.keySet();
      }
  
      /**
       * Sets the given map value for the given key, unless either of them is null.<p>
       *
       * If the value is null,
       *
       * @param key the key
       * @param value the value
       *
       * @return the old value
       *
       * @see java.util.Map#put(java.lang.Object, java.lang.Object)
       */
      public V put(K key, V value) {
  
          if ((key != null) && (value != null)) {
              return m_internalMap.put(key, value);
          }
          Exception e = new Exception();
          try {
              // we want to print a stack trace when null is used as a key/value
              throw e;
          } catch (Exception e2) {
              e = e2;
          }
          if (key == null) {
              LOG.warn("Invalid null key in map", e);
              return null;
          }
          if (value == null) {
              LOG.warn("Invalid null value in map", e);
              return m_internalMap.remove(key);
          }
          return null;
      }
  
      /**
       * @see java.util.Map#putAll(java.util.Map)
       */
      public void putAll(Map<? extends K, ? extends V> m) {
  
          for (Map.Entry<? extends K, ? extends V> entry : m.entrySet()) {
              put(entry.getKey(), entry.getValue());
          }
      }
  
      /**
       * @see java.util.Map#remove(java.lang.Object)
       */
      public V remove(Object key) {
  
          return m_internalMap.remove(key);
      }
  
      /**
       * @see java.util.Map#size()
       */
      public int size() {
  
          return m_internalMap.size();
      }
  
      /**
       * @see java.lang.Object#toString()
       */
      @Override
      public String toString() {
  
          return "" + m_internalMap;
      }
  
      /**
       * @see java.util.Map#values()
       */
      public Collection<V> values() {
  
          return m_internalMap.values();
      }
  
  }
  