Where to close java PreparedStatements and ResultSets?

Question

Consider the code:

PreparedStatement ps = null;
ResultSet rs = null;
try {
  ps = conn.createStatement(myQueryString);
  rs = ps.executeQuery();
  // process         


        

Answer 1

Building on @erickson's answer, why not just do it in one try block like this?

private void doEverythingInOneSillyMethod(String key) throws MyAppException
{
  try (Connection db = ds.getConnection();
       PreparedStatement ps = db.prepareStatement(...)) {

    db.setReadOnly(true);
    ps.setString(1, key);
    ResultSet rs = ps.executeQuery()
    ...
  } catch (SQLException ex) {
    throw new MyAppException("Query failed.", ex);
  }
}

Note that you don't need to create the ResultSet object inside the try block as ResultSet's are automatically closed when the PreparedStatement object is closed.

A ResultSet object is automatically closed when the Statement object that generated it is closed, re-executed, or used to retrieve the next result from a sequence of multiple results.

Reference: https://docs.oracle.com/javase/7/docs/api/java/sql/ResultSet.html