/*
 * Copyright 2002 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.jms;

/** A <CODE>Connection</CODE> object is a client's active connection to its JMS 
  * provider. It typically allocates provider resources outside the Java virtual
  * machine (JVM).
  *
  * <P>Connections support concurrent use.
  *
  * <P>A connection serves several purposes:
  *
  * <UL>
  *   <LI>It encapsulates an open connection with a JMS provider. It 
  *       typically represents an open TCP/IP socket between a client and 
  *       a provider service daemon.
  *   <LI>Its creation is where client authentication takes place.
  *   <LI>It can specify a unique client identifier.
  *   <LI>It provides a <CODE>ConnectionMetaData</CODE> object.
  *   <LI>It supports an optional <CODE>ExceptionListener</CODE> object.
  * </UL>
  *
  * <P>Because the creation of a connection involves setting up authentication 
  * and communication, a connection is a relatively heavyweight 
  * object. Most clients will do all their messaging with a single connection.
  * Other more advanced applications may use several connections. The JMS API
  * does 
  * not architect a reason for using multiple connections; however, there may 
  * be operational reasons for doing so.
  *
  * <P>A JMS client typically creates a connection, one or more sessions, 
  * and a number of message producers and consumers. When a connection is
  * created, it is in stopped mode. That means that no messages are being
  * delivered.
  *
  * <P>It is typical to leave the connection in stopped mode until setup 
  * is complete (that is, until all message consumers have been 
  * created).  At that point, the client calls 
  * the connection's <CODE>start</CODE> method, and messages begin arriving at 
  * the connection's consumers. This setup
  * convention minimizes any client confusion that may result from 
  * asynchronous message delivery while the client is still in the process 
  * of setting itself up.
  *
  * <P>A connection can be started immediately, and the setup can be done 
  * afterwards. Clients that do this must be prepared to handle asynchronous 
  * message delivery while they are still in the process of setting up.
  *
  * <P>A message producer can send messages while a connection is stopped.
  *
  * @version     1.0 - 3 August 1998
  * @author      Mark Hapner
  * @author      Rich Burridge
  *
  * @see         javax.jms.ConnectionFactory
  * @see         javax.jms.QueueConnection
  * @see         javax.jms.TopicConnection
  */

public interface Connection {

    /** Gets the client identifier for this connection.
      *  
      * <P>This value is specific to the JMS provider.  It is either preconfigured 
      * by an administrator in a <CODE>ConnectionFactory</CODE> object
      * or assigned dynamically by the application by calling the
      * <code>setClientID</code> method.
      * 
      * 
      * @return the unique client identifier
      *  
      * @exception JMSException if the JMS provider fails to return
      *                         the client ID for this connection due
      *                         to some internal error.
      *
      **/
    String
    getClientID() throws JMSException;


    /** Sets the client identifier for this connection.
      *  
      * <P>The preferred way to assign a JMS client's client identifier is for
      * it to be configured in a client-specific <CODE>ConnectionFactory</CODE>
      * object and transparently assigned to the <CODE>Connection</CODE> object
      * it creates.
      * 
      * <P>Alternatively, a client can set a connection's client identifier
      * using a provider-specific value. The facility to set a connection's
      * client identifier explicitly is not a mechanism for overriding the
      * identifier that has been administratively configured. It is provided
      * for the case where no administratively specified identifier exists.
      * If one does exist, an attempt to change it by setting it must throw an
      * <CODE>IllegalStateException</CODE>. If a client sets the client identifier
      * explicitly, it must do so immediately after it creates the connection 
      * and before any other
      * action on the connection is taken. After this point, setting the
      * client identifier is a programming error that should throw an
      * <CODE>IllegalStateException</CODE>.
      *
      * <P>The purpose of the client identifier is to associate a connection and
      * its objects with a state maintained on behalf of the client by a 
      * provider. The only such state identified by the JMS API is that required
      * to support durable subscriptions.
      *
      * <P>If another connection with the same <code>clientID</code> is already running when
      * this method is called, the JMS provider should detect the duplicate ID and throw
      * an <CODE>InvalidClientIDException</CODE>.
      *
      * @param clientID the unique client identifier
      * 
      * @exception JMSException if the JMS provider fails to
      *                         set the client ID for this connection due
      *                         to some internal error.
      *
      * @exception InvalidClientIDException if the JMS client specifies an
      *                         invalid or duplicate client ID.
      * @exception IllegalStateException if the JMS client attempts to set
      *       a connection's client ID at the wrong time or
      *       when it has been administratively configured.
      */

    void
    setClientID(String clientID) throws JMSException;

 
    /** Gets the metadata for this connection.
      *  
      * @return the connection metadata
      *  
      * @exception JMSException if the JMS provider fails to
      *                         get the connection metadata for this connection.
      *
      * @see javax.jms.ConnectionMetaData
      */

    ConnectionMetaData
    getMetaData() throws JMSException;

    /**
     * Gets the <CODE>ExceptionListener</CODE> object for this connection.
     *
     * @return the <CODE>ExceptionListener</CODE> for this connection
     *
     * @exception JMSException if the JMS provider fails to
     *                         get the <CODE>ExceptionListener</CODE> for this 
     *                         connection.
     */

    ExceptionListener 
    getExceptionListener() throws JMSException;


    /** Sets an exception listener for this connection.
      *
      * <P>If a JMS provider detects a serious problem with a connection, it
      * informs the connection's <CODE>ExceptionListener</CODE>, if one has been
      * registered. It does this by calling the listener's
      * <CODE>onException</CODE> method, passing it a <CODE>JMSException</CODE>
      * object describing the problem.
      *
      * <P>An exception listener allows a client to be notified of a problem
      * asynchronously.
      * Some connections only consume messages, so they would have no other 
      * way to learn their connection has failed.
      *
      * <P>A connection serializes execution of its
      * <CODE>ExceptionListener</CODE>.
      *
      * <P>A JMS provider should attempt to resolve connection problems 
      * itself before it notifies the client of them.
      *
      * @param listener the exception listener
      *
      * @exception JMSException if the JMS provider fails to
      *                         set the exception listener for this connection.
      */

    void 
    setExceptionListener(ExceptionListener listener) throws JMSException;

    /** Starts (or restarts) a connection's delivery of incoming messages.
      * A call to <CODE>start</CODE> on a connection that has already been
      * started is ignored.
      * 
      * @exception JMSException if the JMS provider fails to start
      *                         message delivery due to some internal error.
      *
      * @see javax.jms.Connection#stop
      */

    void
    start() throws JMSException;

 
    /** Temporarily stops a connection's delivery of incoming messages.
      * Delivery can be restarted using the connection's <CODE>start</CODE>
      * method. When the connection is stopped,
      * delivery to all the connection's message consumers is inhibited:
      * synchronous receives block, and messages are not delivered to message
      * listeners.
      *
      * <P>This call blocks until receives and/or message listeners in progress
      * have completed.
      *
      * <P>Stopping a connection has no effect on its ability to send messages.
      * A call to <CODE>stop</CODE> on a connection that has already been
      * stopped is ignored.
      *
      * <P>A call to <CODE>stop</CODE> must not return until delivery of messages
      * has paused. This means that a client can rely on the fact that none of 
      * its message listeners will be called and that all threads of control 
      * waiting for <CODE>receive</CODE> calls to return will not return with a 
      * message until the
      * connection is restarted. The receive timers for a stopped connection
      * continue to advance, so receives may time out while the connection is
      * stopped.
      * 
      * <P>If message listeners are running when <CODE>stop</CODE> is invoked, 
      * the <CODE>stop</CODE> call must
      * wait until all of them have returned before it may return. While these
      * message listeners are completing, they must have the full services of the
      * connection available to them.
      *  
      * @exception JMSException if the JMS provider fails to stop
      *                         message delivery due to some internal error.
      *
      * @see javax.jms.Connection#start
      */

    void
    stop() throws JMSException;

 
    /** Closes the connection.
      *
      * <P>Since a provider typically allocates significant resources outside 
      * the JVM on behalf of a connection, clients should close these resources
      * when they are not needed. Relying on garbage collection to eventually 
      * reclaim these resources may not be timely enough.
      *
      * <P>There is no need to close the sessions, producers, and consumers
      * of a closed connection.
      *
      * <P>Closing a connection causes all temporary destinations to be
      * deleted.
      *
      * <P>When this method is invoked, it should not return until message
      * processing has been shut down in an orderly fashion. This means that all
      * message 
      * listeners that may have been running have returned, and that all pending 
      * receives have returned. A close terminates all pending message receives 
      * on the connection's sessions' consumers. The receives may return with a 
      * message or with null, depending on whether there was a message available 
      * at the time of the close. If one or more of the connection's sessions' 
      * message listeners is processing a message at the time when connection 
      * <CODE>close</CODE> is invoked, all the facilities of the connection and 
      * its sessions must remain available to those listeners until they return 
      * control to the JMS provider. 
      *
      * <P>Closing a connection causes any of its sessions' transactions
      * in progress to be rolled back. In the case where a session's
      * work is coordinated by an external transaction manager, a session's 
      * <CODE>commit</CODE> and <CODE>rollback</CODE> methods are
      * not used and the result of a closed session's work is determined
      * later by the transaction manager.
      *
      * Closing a connection does NOT force an 
      * acknowledgment of client-acknowledged sessions. 
      * 
      * <P>Invoking the <CODE>acknowledge</CODE> method of a received message 
      * from a closed connection's session must throw an 
      * <CODE>IllegalStateException</CODE>.  Closing a closed connection must 
      * NOT throw an exception.
      *  
      * @exception JMSException if the JMS provider fails to close the
      *                         connection due to some internal error. For 
      *                         example, a failure to release resources
      *                         or to close a socket connection can cause
      *                         this exception to be thrown.
      *
      */

    void 
    close() throws JMSException; 
}