connectioncontext.java

OpenJMS是一个开源的Java Message Service API 1.0.2 规范的实现,它包含有以下特性： *. 它既支持点到点（point-to-point）（PTP）模型和发布/订

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 *    please contact [e-mail].
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 *
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 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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 *
 * Copyright 2004-2005 (C) Exoffice Technologies Inc. All Rights Reserved.
 *
 * $Id: ConnectionContext.java,v 1.5 2005/12/01 13:44:38 tanderson Exp $
 */
package org.exolab.jms.net.connector;

import java.security.Principal;
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.exolab.jms.net.uri.URI;


/**
 * <code>ConnectionContext</code> enables connectors to associate a {@link
 * Connection} and {@link ConnectionFactory} with th current thread, to enable
 * deserialized {@link org.exolab.jms.net.proxy.Proxy} instances to resolve a
 * {@link Connection} back to the server.
 *
 * @author <a href="mailto:[e-mail]">Tim Anderson</a>
 * @version $Revision: 1.5 $ $Date: 2005/12/01 13:44:38 $
 */
public final class ConnectionContext {

    /**
     * Maintains a List of {@link Context} instances on a per-thread basis.
     */
    private static ThreadLocal _contexts = new ThreadLocal();

    /**
     * The logger.
     */
    private static final Log _log = LogFactory.getLog(ConnectionContext.class);


    /**
     * Prevent construction of helper class.
     */
    private ConnectionContext() {
    }

    /**
     * Adds the connection context for the current thread.
     *
     * @param principal the security principal
     * @param factory   the connection factory
     */
    public static void push(Principal principal, ConnectionFactory factory) {
        List stack = (List) _contexts.get();
        if (stack == null) {
            stack = new ArrayList(2);
            _contexts.set(stack);
        }
        stack.add(new Context(principal, factory));
    }

    /**
     * Removes the last-pushed context for the current thread.
     */
    public static void pop() {
        List stack = (List) _contexts.get();
        stack.remove(stack.size() - 1);
    }

    /**
     * Returns a connection using the principal and connection factory
     * associated with the current thread.
     *
     * @param uri the URI
     * @return a new connection, or <code>null</code> if a connection can't
     *         be established
     */
    public static Connection getConnection(URI uri) {
        Connection result = null;
        Context context = top();
        if (context != null) {
            ConnectionFactory factory = context.getConnectionFactory();
            try {
                result = factory.getConnection(context.getPrincipal(), uri);
            } catch (ResourceException exception) {
                _log.debug(exception, exception);
            }
        }
        return result;
    }

    /**
     * Returns the connection factory for the current thread.
     *
     * @return the connection factory for the current thread, or
     *         <code>null</code> if no factory is set
     */
    public static ConnectionFactory getConnectionFactory() {
        ConnectionFactory result = null;
        Context context = top();
        if (context != null) {
            result = context.getConnectionFactory();
        }
        return result;
    }

    /**
     * Returns the context at the top of the local threads stack.
     *
     * @return the top context, or <code>null</code> if there are no contexts
     *         associated with this thread.
     */
    private static Context top() {
        Context context = null;
        List stack = (List) _contexts.get();
        if (stack != null && !stack.isEmpty()) {
            context = (Context) stack.get(stack.size() - 1);
        }
        return context;
    }


    private static class Context {

        /**
         * The security principal.
         */
        private final Principal _principal;

        /**
         * The connection factory.
         */
        private final ConnectionFactory _factory;


        /**
         * Construct a new <code>Context</code>.
         *
         * @param principal the security principal
         * @param factory   the connection factory
         */
        public Context(Principal principal, ConnectionFactory factory) {
            _principal = principal;
            _factory = factory;
        }

        /**
         * Returns the security principal.
         *
         * @return the security principal
         */
        public Principal getPrincipal() {
            return _principal;
        }

        /**
         * Returns the connection factory.
         *
         * @return the connection factory.
         */
        public ConnectionFactory getConnectionFactory() {
            return _factory;
        }

    }
}