Java multiple threads database access [closed]

Answer 1

I tumbled into this problem when working with a multi-threaded Java program that was using a Sqllite database. It uses file locking so I had to make sure that only one thread was doing work at the same time.

I basically ended up with using synchronized. When the ConnectionFactory returns a db connection, it also returns a lock object that one should lock when using the connection. So you could do synchronization lock manually, or create a subclass of the class below which does it for you:

 /**
  * Subclass this class and implement the persistInTransaction method to perform
  * an update to the database.
  */
 public abstract class DBOperationInTransaction {

     protected Logger logger = Logger.getLogger(DBOperationInTransaction.class.getName());

     public DBOperationInTransaction(ConnectionFactory connectionFactory) {
         DBConnection con = null;

         try {
             con = connectionFactory.getConnection();

             if(con == null) {
                 logger.log(Level.SEVERE, "Could not get db connection");
                 throw new RuntimException("Could not get db connection");
             }

             synchronized (con.activityLock) {
                 con.connection.setAutoCommit(false);
                 persistInTransaction(con.connection);
                 con.connection.commit();
             }

         } catch (Exception e) {
             logger.log(Level.SEVERE, "Failed to persist data:", e);
             throw new RuntimeException(e);
         } finally {
             if(con != null) {
                 //Close con.connection silently.
             }
         }
     }

     /**
      * Method for persisting data within a transaction. If any SQLExceptions
      * occur they are logged and the transaction is rolled back.
      * 
      * In the scope of the method there is a logger object available that any
      * errors/warnings besides sqlException that you want to log.
      * 
      * @param con
      *            Connection ready for use, do not do any transaction handling
      *            on this object.
      * @throws SQLException
      *             Any SQL exception that your code might throw. These errors
      *             are logged. Any exception will rollback the transaction.
      * 
      */
     abstract protected void persistInTransaction(Connection con) throws SQLException;

 }

And the DBConnection struct:

 final public class DBConnection {
     public final Connection connection;
     public final String activityLock;

     public DBConnection(Connection connection, String activityLock) {
         this.connection = connection;
         this.activityLock = activityLock;
     }

 }