When I execute the following code, I get an exception. I think it is because I'm preparing in new statement with he same connection object. How should I rewrite this so that I can create a prepared statement AND get to use rs2? Do I have to create a new connection object even if the connection is to the same DB?
try { //Get some stuff String name = ""; String sql = "SELECT `name` FROM `user` WHERE `id` = " + userId + " LIMIT 1;"; ResultSet rs = statement.executeQuery(sql); if(rs.next()) { name = rs.getString("name"); } String sql2 = "SELECT `id` FROM `profiles` WHERE `id` =" + profId + ";"; ResultSet rs2 = statement.executeQuery(sql2); String updateSql = "INSERT INTO `blah`............"; PreparedStatement pst = (PreparedStatement)connection.prepareStatement(updateSql); while(rs2.next()) { int id = rs2.getInt("id"); int stuff = getStuff(id); pst.setInt(1, stuff); pst.addBatch(); } pst.executeBatch(); } catch (Exception e) { e.printStackTrace(); } private int getStuff(int id) { try { String sql = "SELECT ......;"; ResultSet rs = statement.executeQuery(sql); if(rs.next()) { return rs.getInt("something"); } return -1; }//code continues
You should explicitly close Statements , ResultSets , and Connections when you no longer need them, unless you declare them in a try -with-resources statement (available in JDK 7 and after). Connections to Derby are resources external to an application, and the garbage collector will not close them automatically.
Once the connection is closed you can no longer use any of the resources (statements, prepared statements, result sets), all of them are automatically closed. So you need to do all of your processing while the resources are open.
The problem is with the way you fetch data in getStuff()
. Each time you visit getStuff()
you obtain a fresh ResultSet
but you don't close it.
This violates the expectation of the Statement
class (see here - http://docs.oracle.com/javase/7/docs/api/java/sql/Statement.html):
By default, only one ResultSet object per Statement object can be open at the same time. Therefore, if the reading of one ResultSet object is interleaved with the reading of another, each must have been generated by different Statement objects. All execution methods in the Statement interface implicitly close a statment's current ResultSet object if an open one exists.
What makes things even worse is the rs
from the calling code. It is also derived off-of the statement
field but it is not closed.
Bottom line: you have several ResultSet
pertaining to the same Statement
object concurrently opened.
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