Spring中常用的Collection工具类的学习

Springd 中CollectionUtils 和Apache的Commons-Collections中部分方法一样,其功能和FileCopyUtils在Spring和Commons-Collection中一样的。

 

public class CollectionUtils {

 /**
  * The shared, singleton empty iterator instance.
  */
 public static final Iterator EMPTY_ITERATOR = new EmptyIterator();

 /**
  * The shared, singleton empty attribute map instance.
  */
 public static final AttributeMap EMPTY_ATTRIBUTE_MAP = new LocalAttributeMap(Collections.EMPTY_MAP);

 /**
  * Private constructor to avoid instantiation.
  */
 private CollectionUtils() {
 }

 /**
  * Factory method that adapts an enumeration to an iterator.
  * @param enumeration the enumeration
  * @return the iterator
  */
 public static Iterator toIterator(Enumeration enumeration) {
  return new EnumerationIterator(enumeration);
 }

 /**
  * Factory method that returns a unmodifiable attribute map with a single entry.
  * @param attributeName the attribute name
  * @param attributeValue the attribute value
  * @return the unmodifiable map with a single element
  */
 public static AttributeMap singleEntryMap(String attributeName, Object attributeValue) {
  return new LocalAttributeMap(attributeName, attributeValue);
 }

 /**
  * Add all given objects to given target list. No duplicates will be added. The contains() method of the given
  * target list will be used to determine whether or not an object is already in the list.
  * @param target the collection to which to objects will be added
  * @param objects the objects to add
  * @return whether or not the target collection changed
  */
 public static boolean addAllNoDuplicates(List target, Object[] objects) {
  if (objects == null || objects.length == 0) {
   return false;
  } else {
   boolean changed = false;
   for (int i = 0; i < objects.length; i++) {
    if (!target.contains(objects[i])) {
     target.add(objects[i]);
     changed = true;
    }
   }
   return changed;
  }
 }

 /**
  * Iterator iterating over no elements (hasNext() always returns false).
  */
 private static class EmptyIterator implements Iterator, Serializable {

  private EmptyIterator() {
  }

  public boolean hasNext() {
   return false;
  }

  public Object next() {
   throw new UnsupportedOperationException("There are no elements");
  }

  public void remove() {
   throw new UnsupportedOperationException("There are no elements");
  }
 }

 /**
  * Iterator wrapping an Enumeration.
  */
 private static class EnumerationIterator implements Iterator {

  private Enumeration enumeration;

  public EnumerationIterator(Enumeration enumeration) {
   this.enumeration = enumeration;
  }

  public boolean hasNext() {
   return enumeration.hasMoreElements();
  }

  public Object next() {
   return enumeration.nextElement();
  }

  public void remove() throws UnsupportedOperationException {
   throw new UnsupportedOperationException("Not supported");
  }
 }
}

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