referencemap.java

在Struts2中的jar包xwork的源代码.版本为2.0.7

  Object makeValueReferenceAware(Object o) {
    return valueReferenceType == STRONG ? o : new ReferenceAwareWrapper(o);
  }

  /**
   * Dereferences elements in {@code in} using
   * {@code referenceType} and puts them in {@code out}. Returns
   * {@code out}.
   */
  <T extends Collection<Object>> T dereferenceCollection(
      ReferenceType referenceType, T in, T out) {
    for (Object reference : in) {
      out.add(dereference(referenceType, reference));
    }
    return out;
  }

  /**
   * Marker interface to differentiate external and internal references.
   */
  interface InternalReference {}

  static int keyHashCode(Object key) {
    return System.identityHashCode(key);
  }

  /**
   * Tests weak and soft references for identity equality. Compares references
   * to other references and wrappers. If o is a reference, this returns true
   * if r == o or if r and o reference the same non null object. If o is a
   * wrapper, this returns true if r's referent is identical to the wrapped
   * object.
   */
  static boolean referenceEquals(Reference r, Object o) {
    // compare reference to reference.
    if (o instanceof InternalReference) {
      // are they the same reference? used in cleanup.
      if (o == r) {
        return true;
      }

      // do they reference identical values? used in conditional puts.
      Object referent = ((Reference) o).get();
      return referent != null && referent == r.get();
    }

    // is the wrapped object identical to the referent? used in lookups.
    return ((ReferenceAwareWrapper) o).unwrap() == r.get();
  }

  /**
   * Big hack. Used to compare keys and values to referenced keys and values
   * without creating more references.
   */
  static class ReferenceAwareWrapper {

    Object wrapped;

    ReferenceAwareWrapper(Object wrapped) {
      this.wrapped = wrapped;
    }

    Object unwrap() {
      return wrapped;
    }

    public int hashCode() {
      return wrapped.hashCode();
    }

    public boolean equals(Object obj) {
      // defer to reference's equals() logic.
      return obj.equals(this);
    }
  }

  /**
   * Used for keys. Overrides hash code to use identity hash code.
   */
  static class KeyReferenceAwareWrapper extends ReferenceAwareWrapper {

    public KeyReferenceAwareWrapper(Object wrapped) {
      super(wrapped);
    }

    public int hashCode() {
      return System.identityHashCode(wrapped);
    }
  }

  class SoftKeyReference extends FinalizableSoftReference<Object>
      implements InternalReference {

    int hashCode;

    public SoftKeyReference(Object key) {
      super(key);
      this.hashCode = keyHashCode(key);
    }

    public void finalizeReferent() {
      delegate.remove(this);
    }

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

    @Override public boolean equals(Object o) {
      return referenceEquals(this, o);
    }
  }

  class WeakKeyReference extends FinalizableWeakReference<Object>
      implements InternalReference {

    int hashCode;

    public WeakKeyReference(Object key) {
      super(key);
      this.hashCode = keyHashCode(key);
    }

    public void finalizeReferent() {
      delegate.remove(this);
    }

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

    @Override public boolean equals(Object o) {
      return referenceEquals(this, o);
    }
  }

  class SoftValueReference extends FinalizableSoftReference<Object>
      implements InternalReference {

    Object keyReference;

    public SoftValueReference(Object keyReference, Object value) {
      super(value);
      this.keyReference = keyReference;
    }

    public void finalizeReferent() {
      delegate.remove(keyReference, this);
    }

    @Override public boolean equals(Object obj) {
      return referenceEquals(this, obj);
    }
  }

  class WeakValueReference extends FinalizableWeakReference<Object>
      implements InternalReference {

    Object keyReference;

    public WeakValueReference(Object keyReference, Object value) {
      super(value);
      this.keyReference = keyReference;
    }

    public void finalizeReferent() {
      delegate.remove(keyReference, this);
    }

    @Override public boolean equals(Object obj) {
      return referenceEquals(this, obj);
    }
  }

  protected interface Strategy {
    public Object execute(ReferenceMap map, Object keyReference,
        Object valueReference);
  }

  protected Strategy putStrategy() {
    return PutStrategy.PUT;
  }

  protected Strategy putIfAbsentStrategy() {
    return PutStrategy.PUT_IF_ABSENT;
  }

  protected Strategy replaceStrategy() {
    return PutStrategy.REPLACE;
  }

  private enum PutStrategy implements Strategy {
    PUT {
      public Object execute(ReferenceMap map, Object keyReference,
          Object valueReference) {
        return map.delegate.put(keyReference, valueReference);
      }
    },

    REPLACE {
      public Object execute(ReferenceMap map, Object keyReference,
          Object valueReference) {
        return map.delegate.replace(keyReference, valueReference);
      }
    },

    PUT_IF_ABSENT {
      public Object execute(ReferenceMap map, Object keyReference,
          Object valueReference) {
        return map.delegate.putIfAbsent(keyReference, valueReference);
      }
    };
  };

  private static PutStrategy defaultPutStrategy;

  protected PutStrategy getPutStrategy() {
    return defaultPutStrategy;
  }


  class Entry implements Map.Entry<K, V> {

    K key;
    V value;

    public Entry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    public K getKey() {
      return this.key;
    }

    public V getValue() {
      return this.value;
    }

    public V setValue(V value) {
      return put(key, value);
    }

    public int hashCode() {
      return key.hashCode() * 31 + value.hashCode();
    }

    public boolean equals(Object o) {
      if (!(o instanceof ReferenceMap.Entry)) {
        return false;
      }

      Entry entry = (Entry) o;
      return key.equals(entry.key) && value.equals(entry.value);
    }

    public String toString() {
      return key + "=" + value;
    }
  }

  static void ensureNotNull(Object o) {
    if (o == null) {
      throw new NullPointerException();
    }
  }

  static void ensureNotNull(Object... array) {
    for (int i = 0; i < array.length; i++) {
      if (array[i] == null) {
        throw new NullPointerException("Argument #" + i + " is null.");
      }
    }
  }

  private void writeObject(ObjectOutputStream out) throws IOException  {
    out.defaultWriteObject();
    out.writeInt(size());
    for (Map.Entry<Object, Object> entry : delegate.entrySet()) {
      Object key = dereferenceKey(entry.getKey());
      Object value = dereferenceValue(entry.getValue());

      // don't persist gc'ed entries.
      if (key != null && value != null) {
        out.writeObject(key);
        out.writeObject(value);
      }
    }
    out.writeObject(null);
  }

  private void readObject(ObjectInputStream in) throws IOException,
      ClassNotFoundException {
    in.defaultReadObject();
    int size = in.readInt();
    this.delegate = new ConcurrentHashMap<Object, Object>(size);
    while (true) {
      K key = (K) in.readObject();
      if (key == null) {
        break;
      }
      V value = (V) in.readObject();
      put(key, value);
    }
  }

}