Example: Handling connection exceptions for session beans in container-managed database transactions

The following code sample demonstrates how to roll back transactions and issue exceptions to the bean client in cases of stale connection exceptions.

//===================START_PROLOG======================================
//
//   5630-A23, 5630-A22,
//   (C) COPYRIGHT International Business Machines Corp. 2002
//   All Rights Reserved
//   Licensed Materials - Property of IBM
//   US Government Users Restricted Rights - Use, duplication or
//   disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
//
//   IBM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
//   ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
//   PURPOSE. IN NO EVENT SHALL IBM BE LIABLE FOR ANY SPECIAL, INDIRECT OR
//   CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
//   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
//   OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE
//   OR PERFORMANCE OF THIS SOFTWARE.
//
//===================END_PROLOG========================================
 package WebSphereSamples.ConnPool;
 import java.util.*; import java.sql.*; import javax.sql.*; import javax.ejb.*; import javax.naming.*;

/*************************************************************************************
* This bean is designed to demonstrate Database Connections in a                      
* Container Managed Transaction Session Bean.  Its transaction attribute               *
* should be set to TX_REQUIRED or TX_REQUIRES_NEW.                                     *
**************************************************************************************
*/ public class ShowEmployeesCMTBean implements SessionBean {
  private javax.ejb.SessionContext mySessionCtx = null;
  final static long serialVersionUID = 3206093459760846163L;
  
  private javax.sql.DataSource ds;

//************************************************************************************
//* ejbActivate calls the getDS method, which does the JNDI lookup for the DataSource.
//* Because the DataSource lookup is in a separate method, we can also invoke it from  
//* the getEmployees method in the case where the DataSource field is null.    
//************************************************************************************ public void ejbActivate() throws java.rmi.EJBException {
  getDS();
}
/**
 * ejbCreate method
 * @exception javax.ejb.CreateException
 * @exception java.rmi.EJBException
 */ public void ejbCreate() throws javax.ejb.CreateException, java.rmi.EJBException {}
/**
 * ejbPassivate method 
 * @exception java.rmi.EJBException
 */ public void ejbPassivate() throws java.rmi.EJBException {}
/**
 * ejbRemove method 
 * @exception java.rmi.EJBException 
 */ public void ejbRemove() throws java.rmi.EJBException {}

//************************************************************************************
//* The getEmployees method runs the database query to retrieve the employees.    
//* The getDS method is only called if the DataSource variable is null.      
//* Because this session bean uses Container Managed Transactions, it cannot retry the  
//* transaction on a StaleConnectionException.  However, it can throw an exception to  
//* its client indicating that the operation is retriable.        *
//************************************************************************************
 public Vector getEmployees() throws com.ibm.ejs.cm.pool.ConnectionWaitTimeoutException, SQLException,
RetryableConnectionException {
   Connection conn  = null;
   Statement stmt = null;
   ResultSet rs = null;
   Vector employeeList = new Vector();

   if (ds == null) getDS();
     
   try {
      // Get a Connection object conn using the DataSource factory.
      conn = ds.getConnection();
      // Run DB query using standard JDBC coding.
      stmt = conn.createStatement();
      String query   = "Select FirstNme, MidInit, LastName " + 
                       "from Employee ORDER BY LastName";
      rs   = stmt.executeQuery(query);
      while (rs.next()) {
         employeeList.addElement(rs.getString(3) + ", " + rs.getString(1) + " " +                                       rs.getString(2));
      }                              }  catch (com.ibm.websphere.ce.cm.StaleConnectionException se) {

// This exception indicates that the connection to the database is no longer valid.
// Rollback the transaction, and throw an exception to the client indicating they
// can retry the transaction if desired.

System.out.println("Stale Connection Exception during get connection or process SQL: " + se.getMessage());

System.out.println("Rolling back transaction and throwing  RetryableConnectionException");

      mySessionCtx.setRollbackOnly();
      throw new RetryableConnectionException(se.toString());
      } 
      catch (com.ibm.ejs.cm.pool.ConnectionWaitTimeoutException cw) {

// This exception is thrown if a connection can not be obtained from the
// pool within a configurable amount of time.  Frequent occurrences of
// this exception indicate an incorrectly tuned connection pool

System.out.println("Connection Wait Timeout Exception during get connection or process SQL: " +
      cw.getMessage());
  throw cw;
      } 
      catch (SQLException sq) {

//Throwing a remote exception will automatically roll back the container managed //transaction

       System.out.println("SQL Exception during get connection or process SQL: " +
        sq.getMessage());
    throw sq;
      } 
      finally {

         // Always close the connection in a finally statement to ensure proper 
         // closure in all cases. Closing the connection does not close and 
         // actual connection, but releases it back to the pool for reuse.

         if (rs != null) {
            try {
      rs.close();
            } 
 catch (Exception e) {
               System.out.println("Close Resultset Exception: " + 
                       e.getMessage());
            }
         }
         if (stmt != null) {
            try {
               stmt.close();
            } 
            catch (Exception e) {
               System.out.println("Close Statement Exception: " + 
                       e.getMessage());
            }
         }
         if (conn != null) {
            try {
               conn.close();
            } 
            catch (Exception e) {
               System.out.println("Close connection exception: " + e.getMessage());
            }
         }
      }
      return employeeList;
}
/**
 * getSessionContext method
 * @return javax.ejb.SessionContext
 */ public javax.ejb.SessionContext getSessionContext() {
  return mySessionCtx;
}
//************************************************************************************
//* The getDS method performs the JNDI lookup for the DataSource.           *
//* This method is called from ejbActivate, and from getEmployees if the DataSource  
//* object is null.                                  *
//************************************************************************************
 private void getDS() {
  try {
    Hashtable parms = new Hashtable();
    parms.put(Context.INITIAL_CONTEXT_FACTORY, 
        "com.ibm.websphere.naming.WsnInitialContextFactory");
    InitialContext ctx = new InitialContext(parms);
    // Perform a naming service lookup to get the DataSource object.
    ds = (DataSource)ctx.lookup("java:comp/env/jdbc/SampleDB");
  } 
       catch (Exception e) {
    System.out.println("Naming service exception: " + e.getMessage());
    e.printStackTrace();
  }
}
/**
 * setSessionContext method 
 * @param ctx javax.ejb.SessionContext
 * @exception java.rmi.EJBException
 */ public void setSessionContext(javax.ejb.SessionContext ctx) throws java.rmi.EJBException {
  mySessionCtx = ctx;
}
}

//===================START_PROLOG======================================
//
//   5630-A23, 5630-A22,
//   (C) COPYRIGHT International Business Machines Corp. 2002
//   All Rights Reserved
//   Licensed Materials - Property of IBM
//   US Government Users Restricted Rights - Use, duplication or
//   disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
//
//   IBM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
//   ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
//   PURPOSE. IN NO EVENT SHALL IBM BE LIABLE FOR ANY SPECIAL, INDIRECT OR
//   CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
//   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
//   OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE
//   OR PERFORMANCE OF THIS SOFTWARE.
//
//===================END_PROLOG========================================
 package WebSphereSamples.ConnPool;

/**
 * This is a Home interface for the Session Bean
 */ public interface ShowEmployeesCMTHome extends javax.ejb.EJBHome {

/**
 * create method for a session bean
* @return WebSphereSamples.ConnPool.ShowEmployeesCMT
 * @exception javax.ejb.CreateException
 * @exception java.rmi.RemoteException
 */ WebSphereSamples.ConnPool.ShowEmployeesCMT create() throws javax.ejb.CreateException,
   java.rmi.RemoteException;
}

//===================START_PROLOG======================================
//
//   5630-A23, 5630-A22,
//   (C) COPYRIGHT International Business Machines Corp. 2002
//   All Rights Reserved
//   Licensed Materials - Property of IBM
//   US Government Users Restricted Rights - Use, duplication or
//   disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
//
//   IBM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
//   ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
//   PURPOSE. IN NO EVENT SHALL IBM BE LIABLE FOR ANY SPECIAL, INDIRECT OR
//   CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
//   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
//   OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE
//   OR PERFORMANCE OF THIS SOFTWARE.
//
//===================END_PROLOG========================================
 package WebSphereSamples.ConnPool;

/**
 * This is an Enterprise Java Bean Remote Interface
 */ public interface ShowEmployeesCMT extends javax.ejb.EJBObject {

/**
 * 
 * @return java.util.Vector
 */ java.util.Vector getEmployees() throws java.sql.SQLException, java.rmi.RemoteException,
 com.ibm.ejs.cm.pool.ConnectionWaitTimeoutException,
     WebSphereSamples.ConnPool.RetryableConnectionException;
}

//===================START_PROLOG======================================
//
//   5630-A23, 5630-A22,
//   (C) COPYRIGHT International Business Machines Corp. 2002
//   All Rights Reserved
//   Licensed Materials - Property of IBM
//   US Government Users Restricted Rights - Use, duplication or
//   disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
//
//   IBM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
//   ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
//   PURPOSE. IN NO EVENT SHALL IBM BE LIABLE FOR ANY SPECIAL, INDIRECT OR
//   CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
//   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
//   OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE
//   OR PERFORMANCE OF THIS SOFTWARE.
//
//===================END_PROLOG========================================
 package WebSphereSamples.ConnPool;

/**
 * Exception indicating that the operation can be retried
 * Creation date: (4/2/2001 10:48:08 AM)
 * @author: Administrator
 */ public class RetryableConnectionException extends Exception {
/**
 * RetryableConnectionException constructor.
 */ public RetryableConnectionException() {
  super();
}
/**
 * RetryableConnectionException constructor.
 * @param s java.lang.String
 */ public RetryableConnectionException(String s) {
  super(s);
}
}

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Example: Handling connection exceptions for session beans in container-managed database transactions

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