josh wrote:

It is bad advice to suggest using the gc() call.

It is also usually better to allocate new objects in the loop than to hang on
to one for multiple iterations.

To the OP:

Provide an SSCCE.
<http://www.physci.org/codes/sscce.html>

You have a memory leak.  It is in your code.  The trick is to find from where.

Without an example that recreates the error we likely cannot help in detail.
Candidates are objects that are not abandoned, contrary to GArlington's
suggestion.  You are probably not close()ing a ResultSet or a Connection,
although that usually would cause problems before OutOfMemory (OOM).

GArlington's suggestion to process records one by one is sound.  Are you
storing many records' worth of information at once?

You probably need to refactor some logic into separate methods and classes.

The SSCCE will show us.

ok I post the code:

st_from = conn.createStatement();

rs_from = st_from.executeQuery(query_from);

ps_into = conn_t.prepareStatement(insert_into);

int i_out_record = 0;
int i_in_record = 0;

while(rs_from.next())
{

i_out_record++;

            out_record += "SELECT su record (" + i_out_record + ")";
            in_record += "INSERT su record (";

            row_error = rs_from.getString(campi_from[0]); // se errore su quale
id

            for(int i=0; i < campi_from.length; i++)
            {
                out_record += campi_from[i] + "=" +
rs_from.getString(campi_from[i]) + "::" ;

                ps_into.setString(i+1, rs_from.getString(campi_from[i])); //
prepara l'insert

                in_values += campi_to[i] + "=" + rs_from.getString(campi_from[i])
+ "::" ;
            }
            out_record = out_record.substring(0, out_record.length()-2); //
tolgo il cancelletto finale

            int res = ps_into.executeUpdate();

            if(res != 0)
            {
                i_in_record++;
                in_record += i_in_record + ")" + in_values;

                // chiudi la statement
                //ps_into.close();
            }

            out_record += "\n";
            in_record += "\n";

            /*
            if(i_out_record > 10)
                break;
                */
        }

        String log = "Per la tabella origine " + tabellaFrom + " processati
in uscita record: " + i_out_record + "\n";
        log += "Per la tabella destinazione " + tabellaTo + " processati in
entrata record: " + i_in_record + "\n";
        log += "-----------------------------------------------------------
\n";
        log += out_record + in_record;

        //out.print(st);
        out.print(log);

    }