JDBCTemplate hangs

Question

I am using JDBCTemplate. For one particular query JDBCTemplate hangs after calling more than 3-4 times, sometimes after 15-20 attempts. I haven't found any bug in my code.

private String getXXX(String table)
{
    System.out.println("Test 1");
    final List<String> data = getJdbcTemplate().queryForList(SELECT_TBL_NME,
                new Object[] { table }, String.class);
    System.out.println("Test 2");
    ret = data.size() > 0 ? data.get(0) : null;
    return ret;
}

Console hangs at "Test 1" without any error if the function is called more than 15 times or sometimes even after the 3rd or 4th call.

Answer 1

The problem seems to be that you aren't closing the connections.

final List data = getJdbcTemplate().queryForList(SELECT_TBL_NME, new Object[] { table}, String.class);

The line above will never end because the JdbcTemplate is waiting to get a connection from your db.

So if your db cannot give you a connection your application is waiting, waiting, waiting and it does nothing with the time.

possible fix: Since you are using Spring, check that you aren't doing operation outside your queryForList method.

I had the same problem few months ago because I was calling the ResultSet.getMetaData() outside my queryForList method and that was't releasing/closing the connection.