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Asked: 2026-05-27T02:24:24+00:00

My application has a memory leak resulting from my usage of JDBC. I have

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My application has a memory leak resulting from my usage of JDBC. I have verified this by looking at a visual dump of the heap and seeing thousands of instances of ResultSet and associated objects. My question, then, is how do I appropriately manage resources used by JDBC so they can be garbage collected? Do I need to call “.close()” for every statement that is used? Do I need to call “.close()” on the ResultSets themselves?

How would you free the memory used by the call:

ResultSet rs = connection.createStatement().executeQuery("some sql query");

??

I see that there are other, very similar, questions. Apologies if this is redundant, but either I don’t quite follow the answers or they don’t seem to apply universally. I am trying to achieve an authoritative answer on how to manage memory when using JDBC.

::EDIT:: Adding some code samples

I have a class that is basically a JDBC helper that I use to simplify database interactions, the main two methods are for executing an insert or update, and for executing select statements.

This one for executing insert or update statements:

public int executeCommand(String sqlCommand) throws SQLException {
    if (connection == null || connection.isClosed()) {
        sqlConnect();
    }
    Statement st = connection.createStatement();
    int ret = st.executeUpdate(sqlCommand);
    st.close();
    return ret;
}

And this one for returning ResultSets from a select:

public ResultSet executeSelect(String select) throws SQLException {
    if (connection == null || connection.isClosed()) {
        sqlConnect();
    }
    ResultSet rs = connection.createStatement().executeQuery(select);
    return rs;
}

After using the executeSelect() method, I always call resultset.getStatement().close()

Examining a heap dump with object allocation tracing on shows statements still being held onto from both of those methods…

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1 Answer

  1. Editorial Team

    You should close the Statement if you are not going to reuse it. It is usually good form to first close the ResultSet as some implementations did not close the ResultSet automatically (even if they should).

    If you are repeating the same queries you should probably use a PreparedStatement to reduce parsing overhead. And if you add parameters to your query you really should use PreparedStatement to avoid risk of sql injection.

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