Middleware Technologies [MCA II Yr, Anna University] by Roy Antony Arnold

Session Beans Constraints

• Session beans disappear from the server, if
  
  • The session bean’s timeout value expires
    
  • The server crashes and is restarted
    
  • The server is shutdown and restarted
    
• If any of these event occurs, state information of the bean is lost.
  

Solutions:

1. Session timeout value is configurable so the timeout value can be increased.
   
2. Server crashes and restarts are fairly rare events.
   
   1. The user can be notified that non-recoverable error has occurred and ask the user to try again later.
      
   2. A copy of the state of the bean can be cached at the client side and a new bean can be recreated in the event of original bean dies.
      
   3. Use a database on the server side to hold the state of the client’s conversation. If the session bean dies during the conversation, the client can reconnect and pass in a unique customer identifier to query the database to retrieve whatever state information was saved prior to the failure of the session beans.
      

• A session bean’s state is not transactional. If the internal state of the bean is modified, the rollback will not affect the session bean’s internal state.
  

Solution:

• The session bean’s state should be reset manually to whatever it was before the transaction began.
  

• A stateless session bean cannot implement the SessionSynchronization interface. Because stateless session beans lack a conversational state and cannot hold a transaction across method invocations.
  
• The final constraint on session beans is that they are not reentrant. If one thread is currently using a session bean, the container will throw a java.rmi.RemoteException in response to any other requests to connect to the session bean.