A new package that defines an interface definition for a 'manageable result'...

A new package that defines an interface definition for a 'manageable result' and an interface + default implementation for managing results. The set-up is as such, that it would be easy to implement another manager that does not need the entire resultset to base its calculations on. That can cause significant performance gains for result sets that are resource expensive to acquire or maintain in memory.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/branches/rsm@9165 b35dd754-fafc-0310-a699-88a17e54d16e

src/java/org/jivesoftware/util/resultsetmanager/Result.java

+package org.jivesoftware.util.resultsetmanager;
+
+/**
+ * Elements from a result set as defined by XEP-0059 have certain
+ * characteristics. This interface defines these characteristics.
+ * 
+ * Applying this interface to a class will allow you to use ResultSet operations
+ * on collections of your class. In other words: you are making collections of
+ * your class managable/navigable.
+ * 
+ * @author Guus der Kinderen, guus@nimbuzz.com
+ * @see http://www.xmpp.org/extensions/xep-0059.html
+ */
+public interface Result {
+
+	/**
+	 * Returns a unique identifier for this Result. Each element in a ResultSet
+	 * must have a distinct UIDs. 
+	 * 
+	 * XEP-0059 says: <quote>(...) the UIDs are
+	 * unique in the context of all possible members of the full result set.
+	 * Each UID MAY be based on part of the content of its associated item (...)
+	 * or on an internal table index. Another possible method is to serialize
+	 * the XML of the item and then hash it to generate the UID. Note: The
+	 * requesting entity MUST treat all UIDs as opaque.</quote>
+	 * 
+	 * @return Unique ID of the Result
+	 */
+	public String getUID();
+
+}
\ No newline at end of file

src/java/org/jivesoftware/util/resultsetmanager/ResultSetImpl.java

+package org.jivesoftware.util.resultsetmanager;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Hashtable;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A result set representation as described in XEP-0059. Note that this result
+ * 'set' actually makes use of a List implementations, as the Java Set
+ * definition disallows duplicate elements, while the List definition supplies
+ * most of the required indexing operations.
+ * 
+ * This ResultSet implementation loads all all results from the set into memory,
+ * which might be undesirable for very large sets, or for sets where the
+ * retrieval of a result is an expensive operation. sets.
+ * 
+ * As most methods are backed by the {@link List#subList(int, int)} method,
+ * non-structural changes in the returned lists are reflected in the ResultSet,
+ * and vice-versa.
+ * 
+ * @author Guus der Kinderen, guus@nimbuzz.com
+ * 
+ * @param <E>
+ *            Each result set should be a collection of instances of the exact
+ *            same class. This class must implement the {@link Result}
+ *            interface.
+ * @see java.util.List#subList(int, int)
+ * 
+ */
+/*
+ * TODO: do we want changes to the returned Lists of methods in this class be
+ * applied to the content of the ResultSet itself? Currently, because of the
+ * usage of java.util.List#subList(int, int), it does. I'm thinking a
+ * immodifiable solution would cause less problems. -Guus
+ */
+public class ResultSetImpl<E extends Result> extends ResultSet<E> {
+
+	/**
+	 * A list of all results in this ResultSet
+	 */
+	public final List<E> resultList;
+
+	/**
+	 * A mapping of the UIDs of all results in resultList, to the index of those
+	 * entries in that list.
+	 */
+	public final Map<String, Integer> uidToIndex;
+
+	/**
+	 * Creates a new Result Set instance, based on a collection of Result
+	 * implementing objects. The collection should contain elements of the exact
+	 * same class only, and cannot contain 'null' elements.
+	 * 
+	 * The order that's being used in the new ResultSet instance is the same
+	 * order in which {@link Collection#iterator()} iterates over the
+	 * collection.
+	 * 
+	 * Note that this constructor throws an IllegalArgumentException if the
+	 * Collection that is provided contains Results that have duplicate UIDs.
+	 * 
+	 * @param results
+	 *            The collection of Results that make up this result set.
+	 */
+	public ResultSetImpl(Collection<E> results) {
+		this(results, null);
+	}
+
+	/**
+	 * Creates a new Result Set instance, based on a collection of Result
+	 * implementing objects. The collection should contain elements of the exact
+	 * same class only, and cannot contain 'null' elements.
+	 * 
+	 * The order that's being used in the new ResultSet instance is defined by
+	 * the supplied Comparator class.
+	 * 
+	 * Note that this constructor throws an IllegalArgumentException if the
+	 * Collection that is provided contains Results that have duplicate UIDs.
+	 * 
+	 * @param results
+	 *            The collection of Results that make up this result set.
+	 * @param comparator
+	 *            The Comparator that defines the order of the Results in this
+	 *            result set.
+	 */
+	public ResultSetImpl(Collection<E> results, Comparator<E> comparator) {
+		if (results == null) {
+			throw new NullPointerException("Argument 'results' cannot be null.");
+		}
+
+		final int size = results.size();
+		resultList = new ArrayList<E>(size);
+		uidToIndex = new Hashtable<String, Integer>(size);
+
+		// sort the collection, if need be.
+		List<E> sortedResults = null;
+		if (comparator != null) {
+			sortedResults = new ArrayList<E>(results);
+			Collections.sort(sortedResults, comparator);
+		}
+
+		int index = 0;
+		// iterate over either the sorted or unsorted collection
+		for (final E result : (sortedResults != null ? sortedResults : results)) {
+			if (result == null) {
+				throw new NullPointerException(
+						"The result set must not contain 'null' elements.");
+			}
+
+			final String uid = result.getUID();
+			if (uidToIndex.containsKey(uid)) {
+				throw new IllegalArgumentException(
+						"The result set can not contain elements that have the same UID.");
+			}
+
+			resultList.add(result);
+			uidToIndex.put(uid, Integer.valueOf(index));
+			index++;
+		}
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#size()
+	 */
+	@Override
+	public int size() {
+		return resultList.size();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#getAfter(E, int)
+	 */
+	@Override
+	public List<E> getAfter(String uid, int maxAmount) {
+		if (uid == null || uid.length() == 0) {
+			throw new NullPointerException("Argument 'uid' cannot be null or an empty String.");
+		}
+
+		if (maxAmount < 1) {
+			throw new IllegalArgumentException(
+					"Argument 'maxAmount' must be a integer higher than zero.");
+		}
+
+		// the result of this method is exclusive 'result'
+		final int index = uidToIndex.get(uid) + 1;
+
+		return get(index, maxAmount);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#getBefore(E, int)
+	 */
+	@Override
+	public List<E> getBefore(String uid, int maxAmount) {
+		if (uid == null || uid.length() == 0) {
+			throw new NullPointerException("Argument 'uid' cannot be null or an empty String.");
+		}
+
+		if (maxAmount < 1) {
+			throw new IllegalArgumentException(
+					"Argument 'maxAmount' must be a integer higher than zero.");
+		}
+
+		// the result of this method is exclusive 'result'
+		final int indexOfLastElement = uidToIndex.get(uid);
+		final int indexOfFirstElement = indexOfLastElement - maxAmount;
+
+		if (indexOfFirstElement < 0) {
+			return get(0, indexOfLastElement);
+		}
+
+		return get(indexOfFirstElement, maxAmount);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#get(int)
+	 */
+	@Override
+	public E get(int index) {
+		return resultList.get(index);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#getFirst(int)
+	 */
+	@Override
+	public List<E> getFirst(int maxAmount) {
+		if (maxAmount < 1) {
+			throw new IllegalArgumentException(
+					"Argument 'maxAmount' must be a integer higher than zero.");
+		}
+
+		return get(0, maxAmount);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#getLast(int)
+	 */
+	@Override
+	public List<E> getLast(int maxAmount) {
+		if (maxAmount < 1) {
+			throw new IllegalArgumentException(
+					"Argument 'maxAmount' must be a integer higher than zero.");
+		}
+
+		final int indexOfFirstElement = size() - maxAmount;
+
+		if (indexOfFirstElement < 0) {
+			return get(0, maxAmount);
+		}
+
+		return get(indexOfFirstElement, maxAmount);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.buzzaa.xmpp.resultsetmanager.ResultSet#get(int, int)
+	 */
+	@Override
+	public List<E> get(int fromIndex, int maxAmount) {
+		if (fromIndex < 0) {
+			throw new IllegalArgumentException(
+					"Argument 'fromIndex' must be zero or higher.");
+		}
+
+		if (maxAmount < 1) {
+			throw new IllegalArgumentException(
+					"Argument 'maxAmount' must be a integer higher than zero.");
+		}
+
+		if (fromIndex >= size()) {
+			return new ArrayList<E>(0);
+		}
+
+		// calculate the last index to return, or return up to the end of last
+		// index if 'amount' surpasses the list length.
+		final int absoluteTo = fromIndex + maxAmount;
+		final int toIndex = (absoluteTo > size() ? size() : absoluteTo);
+
+		return resultList.subList(fromIndex, toIndex);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.jivesoftware.util.resultsetmanager.ResultSet#indexOf(java.lang.String)
+	 */
+	@Override
+	public int indexOf(String uid) {
+		return uidToIndex.get(uid).intValue();
+	}
+}