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/ResultSet.java

+package org.jivesoftware.util.resultsetmanager;
+
+import java.util.AbstractCollection;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+
+import org.dom4j.DocumentHelper;
+import org.dom4j.Element;
+import org.dom4j.QName;
+
+/**
+ * A result set representation as described in XEP-0059. A result set is a
+ * collection of objects that each have a unique identifier (UID).
+ * 
+ * It's expected that some implementations will have the complete result set
+ * loaded into memory, whereas more complex implementations might keep
+ * references to partial sets only. This latter would have considerable
+ * advantages if the result set is extremely large, or if the operation to get
+ * all results in the set is expensive.
+ * 
+ * @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.
+ */
+public abstract class ResultSet<E extends Result> extends AbstractCollection<E> {
+
+	/**
+	 * A list of field names that are valid in jabber:iq:search
+	 */
+	private final static Collection<String> validRequestFields = new ArrayList<String>();
+	static {
+		validRequestFields.add("max"); // required
+		validRequestFields.add("before");
+		validRequestFields.add("after");
+		validRequestFields.add("index");
+	}
+
+	/**
+	 * The namespace that identifies Result Set Management functionality.
+	 */
+	public static final String NAMESPACE_RESULT_SET_MANAGEMENT = "http://jabber.org/protocol/rsm";
+
+	/**
+	 * Returns a List of results starting with the first result after the
+	 * provided result (the returned List is exclusive).
+	 * 
+	 * The lenght of the list is equal to 'maxAmount', unless there are no more
+	 * elements available (in which case the length of the result will be
+	 * truncated).
+	 * 
+	 * @param result
+	 *            The element that is right before the first element in the
+	 *            result.
+	 * @param maxAmount
+	 *            The maximum number of elements to return.
+	 * @return A List of elements the are exactly after the element that is
+	 *         provided as a parameter.
+	 * @throws NullPointerException
+	 *             if the result does not exist in the result set.
+	 */
+	public List<E> getAfter(E result, int maxAmount) {
+		return getAfter(result.getUID(), maxAmount);
+	}
+
+	/**
+	 * Returns a List of results starting with the first result after the result
+	 * that's identified by the provided UID (the returned List is exclusive).
+	 * 
+	 * The lenght of the list is equal to 'maxAmount', unless there are no more
+	 * elements available (in which case the length of the result will be
+	 * truncated).
+	 * 
+	 * @param uid
+	 *            The UID of the element that is right before the first element
+	 *            in the result.
+	 * @param maxAmount
+	 *            The maximum number of elements to return.
+	 * @return A List of elements the are exactly after the element that is
+	 *         provided as a parameter.
+	 * @throws NullPointerException
+	 *             if there is no result in the result set that matches the UID.
+	 */
+	public abstract List<E> getAfter(String uid, int maxAmount);
+
+	/**
+	 * Returns a list of results ending with the element right before the
+	 * provided result (the returned List is exclusive).
+	 * 
+	 * At most 'maxAmount' elements are in the returned List, but the lenght of
+	 * the result might be smaller if no more applicable elements are available.
+	 * 
+	 * Note that the order of the result is equal to the order of the results of
+	 * other methods of this class: the last element in the returned List
+	 * immediately preceeds the element denoted by the 'result' parameter.
+	 * 
+	 * @param result
+	 *            The element preceding the last element returned by this
+	 *            function.
+	 * @param maxAmount
+	 *            The length of the List that is being returned.
+	 * @return A List of elements that are exactly before the element that's
+	 *         provided as a parameter.
+	 * @throws NullPointerException
+	 *             if the result does not exist in the result set.
+	 * 
+	 */
+	public List<E> getBefore(E result, int maxAmount) {
+		return getBefore(result.getUID(), maxAmount);
+	}
+
+	/**
+	 * Returns a list of results ending with the element right before the
+	 * element identified by the provided UID (the returned List is exclusive).
+	 * 
+	 * At most 'maxAmount' elements are in the returned List, but the lenght of
+	 * the result might be smaller if no more applicable elements are available.
+	 * 
+	 * Note that the order of the result is equal to the order of the results of
+	 * other methods of this class: the last element in the returned List
+	 * immediately preceeds the element denoted by the 'result' parameter.
+	 * 
+	 * @param uid
+	 *            The UID of the element preceding the last element returned by
+	 *            this function.
+	 * @param maxAmount
+	 *            The length of the List that is being returned.
+	 * @return A List of elements that are exactly before the element that's
+	 *         provided as a parameter.
+	 * @throws NullPointerException
+	 *             if there is no result in the result set that matches the UID.
+	 */
+	public abstract List<E> getBefore(String uid, int maxAmount);
+
+	/**
+	 * Returns the first elements from this result set.
+	 * 
+	 * @param maxAmount
+	 *            the number of elements to return.
+	 * @return the last 'maxAmount' elements of this result set.
+	 */
+	public abstract List<E> getFirst(int maxAmount);
+
+	/**
+	 * Returns the last elements from this result set.
+	 * 
+	 * @param maxAmount
+	 *            the number of elements to return.
+	 * @return the last 'maxAmount' elements of this result set.
+	 */
+	public abstract List<E> getLast(int maxAmount);
+
+	/**
+	 * Returns the element denoted by the index.
+	 * 
+	 * @param index
+	 *            Index of the element to be returned
+	 * @return the Element at 'index'.
+	 */
+	public abstract E get(int index);
+
+	/**
+	 * Returns a list of results, starting with the result that's at the
+	 * specified index. If the difference between the startIndex and the index
+	 * of the last element in the entire resultset is smaller than the size
+	 * supplied in the 'amount' parameter, the length of the returned list will
+	 * be smaller than the 'amount' paramater. If the supplied index is equal
+	 * to, or larger than the size of the result set, an empty List is returned.
+	 * 
+	 * @param fromIndex
+	 *            The index of the first element to be returned.
+	 * @param maxAmount
+	 *            The maximum number of elements to return.
+	 * @return A list of elements starting with (inclusive) the element
+	 *         referenced by 'fromIndex'. An empty List if startIndex is equal
+	 *         to or bigger than the size of this entire result set.
+	 */
+	public abstract List<E> get(int fromIndex, int maxAmount);
+
+	/**
+	 * Returns the UID of the object at the specified index in this result set.
+	 * 
+	 * @param index
+	 *            The index of the UID to be returned.
+	 * @return UID of the object on the specified index.
+	 */
+	public String getUID(int index) {
+		return get(index).getUID();
+	}
+
+	/**
+	 * Returns the index in the full resultset of the element identified by the
+	 * UID in te supplied argument.
+	 * 
+	 * @param uid
+	 *            The UID of the element to search for
+	 * @return The index of the element.
+	 * @throws NullPointerException
+	 *             if there is no result in the result set that matches the UID.
+	 * 
+	 */
+	public abstract int indexOf(String uid);
+
+	/**
+	 * Returns the index in the full resultset of the supplied argument.
+	 * 
+	 * @param element
+	 *            The element to search for
+	 * @return The index of the element.
+	 */
+	public int indexOf(E element) {
+		return indexOf(element.getUID());
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.util.AbstractCollection#iterator()
+	 */
+	@Override
+	public Iterator<E> iterator() {
+		return new Itr();
+	}
+
+	/**
+	 * Applies the 'result set management' directives to this result set, and
+	 * returns a list of Results that matches the directives. Note that the
+	 * orignal set is untouched. Instead, a new List is returned.
+	 * 
+	 * @param rsmElement
+	 *            The XML element that contains the 'result set management'
+	 *            directives.
+	 */
+	public List<E> applyRSMDirectives(Element rsmElement) {
+		if (rsmElement == null || !isValidRSMRequest(rsmElement)) {
+			throw new IllegalArgumentException(
+					"The 'rsmElement' argument must be a valid, non-null RSM element.");
+		}
+
+		final int max = Integer.parseInt(rsmElement.element("max").getText());
+
+		if (max == 0) {
+			// this is a request for a resultset count.
+			return Collections.emptyList();
+		}
+
+		// optional elements
+		final Element afterElement = rsmElement.element("after");
+		final Element beforeElement = rsmElement.element("before");
+		final Element indexElement = rsmElement.element("index");
+
+		// Identify the pointer object in this set. This is the object before
+		// (or after) the first (respectivly last) element of the subset that
+		// should be returned. If no pointer is specified, the pointer is said
+		// to be before or after the first respectivly last element of the set.
+		String pointerUID = null; // by default, the pointer is before the
+		// first element of the set.
+
+		// by default, the search list is forward oriented.
+		boolean isForwardOriented = true;
+
+		if (afterElement != null) {
+			pointerUID = afterElement.getText();
+		} else if (beforeElement != null) {
+			pointerUID = beforeElement.getText();
+			isForwardOriented = false;
+		} else if (indexElement != null) {
+			final int index = Integer.parseInt(indexElement.getText());
+			if (index > 0) {
+				pointerUID = getUID(index - 1);
+			}
+		}
+
+		if (pointerUID != null && pointerUID.equals("")) {
+			pointerUID = null;
+		}
+
+		if (isForwardOriented) {
+			if (pointerUID == null) {
+				return getFirst(max);
+			}
+			return getAfter(pointerUID, max);
+		}
+
+		if (pointerUID == null) {
+			return getLast(max);
+		}
+		return getBefore(pointerUID, max);
+	}
+
+	/**
+	 * Generates a Result Set Management 'set' element that describes the parto
+	 * of the result set that was generated. You typically would use the List
+	 * that was returned by {@link #applyRSMDirectives(Element)} as an argument
+	 * to this method.
+	 * 
+	 * @param returnedResults
+	 *            The subset of Results that is returned by the current query.
+	 * @return An Element named 'set' that can be included in the result IQ
+	 *         stanza, which returns the subset of results.
+	 */
+	public Element generateSetElementFromResults(List<E> returnedResults) {
+		if (returnedResults == null) {
+			throw new IllegalArgumentException(
+					"Argument 'returnedResults' cannot be null.");
+		}
+		final Element setElement = DocumentHelper.createElement(QName.get(
+				"set", ResultSet.NAMESPACE_RESULT_SET_MANAGEMENT));
+		// the size element contains the size of this entire result set.
+		setElement.addElement("count").setText(String.valueOf(size()));
+
+		// if the query wasn't a 'count only' query, add two more elements
+		if (returnedResults.size() > 0) {
+			final Element firstElement = setElement.addElement("first");
+			firstElement.addText(returnedResults.get(0).getUID());
+			firstElement.addAttribute("index", String
+					.valueOf(indexOf(returnedResults.get(0))));
+
+			setElement.addElement("last").addText(
+					returnedResults.get(returnedResults.size() - 1).getUID());
+		}
+
+		return setElement;
+	}
+
+	/**
+	 * Checks if the Element that has been passed as an argument is a valid
+	 * Result Set Management element, in a request context.
+	 * 
+	 * @param rsmElement
+	 *            The Element to check.
+	 * @return ''true'' if this is a valid RSM query representation, ''false''
+	 *         otherwise.
+	 */
+	// Dom4J doesn't do generics, sadly.
+	@SuppressWarnings("unchecked")
+	public static boolean isValidRSMRequest(Element rsmElement) {
+		if (rsmElement == null) {
+			throw new IllegalArgumentException(
+					"The argument 'rsmElement' cannot be null.");
+		}
+
+		if (!rsmElement.getName().equals("set")) {
+			// the name of the element must be "set".
+			return false;
+		}
+
+		if (!rsmElement.getNamespaceURI().equals(
+				NAMESPACE_RESULT_SET_MANAGEMENT)) {
+			// incorrect namespace
+			return false;
+		}
+
+		final Element maxElement = rsmElement.element("max");
+		if (maxElement == null) {
+			// The 'max' element in an RSM request must be available
+			return false;
+		}
+
+		final String sMax = maxElement.getText();
+		if (sMax == null || sMax.length() == 0) {
+			// max element must contain a value.
+			return false;
+		}
+
+		try {
+			if (Integer.parseInt(sMax) < 0) {
+				// must be a postive integer.
+				return false;
+			}
+		} catch (NumberFormatException e) {
+			// the value of 'max' must be an integer value.
+			return false;
+		}
+
+		List<Element> allElements = rsmElement.elements();
+		int optionalElements = 0;
+		for (Element element : allElements) {
+			final String name = element.getName();
+			if (!validRequestFields.contains(name)) {
+				// invalid element.
+				return false;
+			}
+
+			if (!name.equals("max")) {
+				optionalElements++;
+			}
+
+			if (optionalElements > 1) {
+				// only one optional element is allowed.
+				return false;
+			}
+
+			if (name.equals("index")) {
+				final String value = element.getText();
+				if (value == null || value.equals("")) {
+					// index elements must have a numberic value.
+					return false;
+				}
+				try {
+					if (Integer.parseInt(value) < 0) {
+						// index values must be positive.
+						return false;
+					}
+				} catch (NumberFormatException e) {
+					// index values must be numeric.
+					return false;
+				}
+			}
+		}
+
+		return true;
+	}
+
+	/**
+	 * Basic Iterator implementation. Forward scrolling only. Does not support
+	 * modification.
+	 * 
+	 * @author Guus der Kinderen, guus@nimbuzz.com
+	 * 
+	 */
+	class Itr implements Iterator<E> {
+		/**
+		 * Index of element to be returned by subsequent call to next.
+		 */
+		int cursor = 0;
+
+		/*
+		 * (non-Javadoc)
+		 * 
+		 * @see java.util.Iterator#hasNext()
+		 */
+		public boolean hasNext() {
+			return cursor != size();
+		}
+
+		/*
+		 * (non-Javadoc)
+		 * 
+		 * @see java.util.Iterator#next()
+		 */
+		public E next() {
+			return get(cursor++);
+		}
+
+		/*
+		 * (non-Javadoc)
+		 * 
+		 * @see java.util.Iterator#remove()
+		 */
+		public void remove() {
+			throw new UnsupportedOperationException();
+		}
+	}
+}
\ 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();
+	}
+}