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/*
 * Copyright (c) 1997, 2017 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package javax.jms;

import java.util.Enumeration;

/**
 * A client uses a {@code QueueBrowser} object to look at messages on a queue without removing them.
 *
 * 
 * The {@code getEnumeration} method returns a {@code java.util.Enumeration} that is used to scan the queue's messages.
 * It may be an enumeration of the entire content of a queue, or it may contain only the messages matching a message
 * selector.
 *
 * 

 * Messages may be arriving and expiring while the scan is done. The Jakarta Messaging API does not require the content of an
 * enumeration to be a static snapshot of queue content. Whether these changes are visible or not depends on the JMS
 * provider.
 * 

 * A message must not be returned by a {@code QueueBrowser} before its delivery time has been reached.
 *
 * 

 * A {@code QueueBrowser} can be created from either a {@code Session} or a {@code  QueueSession}.
 *
 * @see javax.jms.Session#createBrowser
 * @see javax.jms.QueueSession#createBrowser
 * @see javax.jms.QueueReceiver
 *
 * @version Jakarta Messaging 2.0
 * @since JMS 1.0
 */
public interface QueueBrowser extends AutoCloseable {

    /**
     * Gets the queue associated with this queue browser.
     *
     * @return the queue
     *
     * @exception JMSException if the Jakarta Messaging provider fails to get the queue associated with this browser due to some internal
     * error.
     */
    Queue getQueue() throws JMSException;

    /**
     * Gets this queue browser's message selector expression.
     *
     * @return this queue browser's message selector, or null if no message selector exists for the message consumer (that
     * is, if the message selector was not set or was set to null or the empty string)
     *
     * @exception JMSException if the Jakarta Messaging provider fails to get the message selector for this browser due to some internal
     * error.
     */
    String getMessageSelector() throws JMSException;

    /**
     * Gets an enumeration for browsing the current queue messages in the order they would be received.
     *
     * @return an enumeration for browsing the messages
     *
     * @exception JMSException if the Jakarta Messaging provider fails to get the enumeration for this browser due to some internal error.
     */
    Enumeration getEnumeration() throws JMSException;

    /**
     * Closes the {@code QueueBrowser}.
     *
     * 
     * Since a provider may allocate some resources on behalf of a QueueBrowser outside the Java virtual machine, clients
     * should close them when they are not needed. Relying on garbage collection to eventually reclaim these resources may
     * not be timely enough.
     *
     * @exception JMSException if the Jakarta Messaging provider fails to close this browser due to some internal error.
     */
    @Override
    void close() throws JMSException;
}