storedkeyset.java

嵌入式数据库Berkeley DB-4.5.20源代码

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2000-2006
 *      Oracle Corporation.  All rights reserved.
 *
 * $Id: StoredKeySet.java,v 12.4 2006/08/31 18:14:08 bostic Exp $
 */

package com.sleepycat.collections;

import java.util.Set;

import com.sleepycat.bind.EntryBinding;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.OperationStatus;

/**
 * The Set returned by Map.keySet() and which can also be constructed directly
 * if a Map is not needed.
 * Since this collection is a set it only contains one element for each key,
 * even when duplicates are allowed.  Key set iterators are therefore
 * particularly useful for enumerating the unique keys of a store or index that
 * allows duplicates.
 *
 * @author Mark Hayes
 */
public class StoredKeySet extends StoredCollection implements Set {

    /**
     * Creates a key set view of a {@link Database}.
     *
     * @param database is the Database underlying the new collection.
     *
     * @param keyBinding is the binding used to translate between key buffers
     * and key objects.
     *
     * @param writeAllowed is true to create a read-write collection or false
     * to create a read-only collection.
     *
     * @throws IllegalArgumentException if formats are not consistently
     * defined or a parameter is invalid.
     *
     * @throws RuntimeExceptionWrapper if a {@link DatabaseException} is
     * thrown.
     */
    public StoredKeySet(Database database, EntryBinding keyBinding,
                        boolean writeAllowed) {

        super(new DataView(database, keyBinding, null, null,
                           writeAllowed, null));
    }

    StoredKeySet(DataView keySetView) {

        super(keySetView);
    }

    /**
     * Adds the specified key to this set if it is not already present
     * (optional operation).
     * When a key is added the value in the underlying data store will be
     * empty.
     * This method conforms to the {@link Set#add} interface.
     *
     * @throws UnsupportedOperationException if the collection is indexed, or
     * if the collection is read-only.
     *
     * @throws RuntimeExceptionWrapper if a {@link DatabaseException} is
     * thrown.
     */
    public boolean add(Object key) {

        DataCursor cursor = null;
        boolean doAutoCommit = beginAutoCommit();
        try {
            cursor = new DataCursor(view, true);
            OperationStatus status = cursor.putNoOverwrite(key, null, false);
            closeCursor(cursor);
            commitAutoCommit(doAutoCommit);
            return (status == OperationStatus.SUCCESS);
        } catch (Exception e) {
            closeCursor(cursor);
            throw handleException(e, doAutoCommit);
        }
    }

    /**
     * Removes the specified key from this set if it is present (optional
     * operation).
     * If duplicates are allowed, this method removes all duplicates for the
     * given key.
     * This method conforms to the {@link Set#remove} interface.
     *
     * @throws UnsupportedOperationException if the collection is read-only.
     *
     * @throws RuntimeExceptionWrapper if a {@link DatabaseException} is
     * thrown.
     */
    public boolean remove(Object key) {

        return removeKey(key, null);
    }

    /**
     * Returns true if this set contains the specified key.
     * This method conforms to the {@link Set#contains} interface.
     *
     * @throws RuntimeExceptionWrapper if a {@link DatabaseException} is
     * thrown.
     */
    public boolean contains(Object key) {

        return containsKey(key);
    }

    boolean hasValues() {

        return false;
    }

    Object makeIteratorData(BaseIterator iterator,
                            DatabaseEntry keyEntry,
                            DatabaseEntry priKeyEntry,
                            DatabaseEntry valueEntry) {

        return view.makeKey(keyEntry, priKeyEntry);
    }

    boolean iterateDuplicates() {

        return false;
    }
}