content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.activemq.web;
  
  import java.util.LinkedList;
  
  import jakarta.jms.Connection;
  import jakarta.jms.ConnectionFactory;
  import jakarta.jms.JMSException;
  import jakarta.jms.Session;
  
  import org.apache.activemq.ActiveMQSession;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * A simple pool of JMS Session objects intended for use by Queue browsers.
   */
  public class SessionPool {
  
      private static final Logger LOG = LoggerFactory.getLogger(SessionPool.class);
  
      private ConnectionFactory connectionFactory;
      private Connection connection;
      private final LinkedList<Session> sessions = new LinkedList<Session>();
  
      public Connection getConnection() throws JMSException {
          if (checkConnection()) {
              return connection;
          }
  
          synchronized (this) {
              try {
                  connection = getConnectionFactory().createConnection();
                  connection.start();
                  return connection;
              } catch (JMSException jmsEx) {
                  LOG.debug("Caught exception while attempting to get a new Connection.", jmsEx);
                  connection.close();
                  connection = null;
                  throw jmsEx;
              }
          }
      }
  
      private boolean checkConnection() {
          if (connection == null) {
              return false;
          }
  
          try {
              connection.getMetaData();
              return true;
          } catch (JMSException e) {
              return false;
          }
      }
  
      public void setConnection(Connection connection) {
          this.connection = connection;
      }
  
      public ConnectionFactory getConnectionFactory() {
          if (connectionFactory == null) {
              throw new IllegalStateException("No ConnectionFactory has been set for the session pool");
          }
          return connectionFactory;
      }
  
      public void setConnectionFactory(ConnectionFactory connectionFactory) {
          this.connectionFactory = connectionFactory;
      }
  
      public Session borrowSession() throws JMSException {
          Session answer = null;
          synchronized (sessions) {
              if (sessions.isEmpty()) {
                  LOG.trace("Creating a new session.");
                  answer = createSession();
              } else {
                  LOG.trace("Serving session from the pool.");
                  answer = sessions.removeLast();
              }
          }
          return answer;
      }
  
      public void returnSession(Session session) {
          if (session != null && !((ActiveMQSession) session).isClosed()) {
              synchronized (sessions) {
                  LOG.trace("Returning session to the pool.");
                  sessions.add(session);
              }
          } else {
              LOG.debug("Session closed or null, not returning to the pool.");
          }
      }
  
      protected Session createSession() throws JMSException {
          return getConnection().createSession(false, Session.AUTO_ACKNOWLEDGE);
      }
  }
  