using JDBC preparedStatement in a batch

Question

Im using Statements batchs to query my data base. Iv'e done some research now and i want to rewrite my application to use preparedStatement instead but i'm having hard time to figure out how to add queries to a preparedStatement batch.

This is what i'm doing now:

private void addToBatch(String sql) throws SQLException{
sttmnt.addBatch(sql);
batchSize++;
if (batchSize == elementsPerExecute){
    executeBatches();
}
}

where sttmnt is a class member of type Statement.

What i want to do is to use the preparedStatement's setString(int, String) method to set some dynamic data and then add it to the batch.

Unfortunately, i don't fully understand how it works, and how i can use setString(int, String) to a specific sql in the batch OR create a new preparedStatemnt for every sql i have and then join them all to one batch.

is it possible to do that? or am i really missing something in my understanding of preparedStatement?

Answer 1

Read the section 6.1.2 of this document for examples. Basically you use the same statement object and invoke the batch method after all the placeholders are set. Another IBM DB2 example which should work for any JDBC implementation. From the second site:

try {
  connection con.setAutoCommit(false);        
  PreparedStatement prepStmt = con.prepareStatement(    
    "UPDATE DEPT SET MGRNO=? WHERE DEPTNO=?");
  prepStmt.setString(1,mgrnum1);            
  prepStmt.setString(2,deptnum1);
  prepStmt.addBatch();                      

  prepStmt.setString(1,mgrnum2);                        
  prepStmt.setString(2,deptnum2);
  prepStmt.addBatch();
  int [] numUpdates=prepStmt.executeBatch();
  for (int i=0; i < numUpdates.length; i++) {
    if (numUpdates[i] == -2)
      System.out.println("Execution " + i + 
        ": unknown number of rows updated");
    else
      System.out.println("Execution " + i + 
        "successful: " + numUpdates[i] + " rows updated");
  }
  con.commit();
} catch(BatchUpdateException b) {
  // process BatchUpdateException
}