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Editorial Team
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Asked: 2026-05-12T14:59:06+00:00

I am processing a large amount of data in a Spring JDBC DAO. The

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I am processing a large amount of data in a Spring JDBC DAO. The DAO directly returns an Iterator over the objects which operates on a bounded BlockingQueue using take() while the retrieval operation is happening in a separate thread (using an ExecutorService).

Inside this thread I see the following behaviour: the retrieval works but certain calls to the ResultSet are causing the call to hang. These calls are

  • isClosed() and
  • isLast()

but not

  • isAfterLast() or
  • isBeforeFirst() or
  • isFirst()

Obviously I need to know what the last element is (in order to insert a special element into the blocking queue that yields false in the iterators hasNext() method). I could work around it by finding out the number of rows in the ResultSet before putting objects into the BlockingQueue but this feels a bit clumsy. Is there a thread-safe way to work with ResultSets?

Switching to a multi-threaded datasource (I tested C3POs ComboPooledDataSource) does not seem to help.

Note: this issue was first (incorrectly) identified by me here

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1 Answer

  1. Editorial Team

    The correct solution is to set an appropriate ResultSet type. The default “TYPE_FORWARD_ONLY” is not supported by isLast(). The type of ResultSet can be set by using a PreparedStatementCreator instead of an SQL string for e.g. query() calls to a JdbcTemplate. Such instances are acquired through a PreparedStatementCreatorFactory. On such a factory the type of the ResultSet (e.g. “TYPE_SCROLL_INSENSITIVE”) can be set.

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