Problemas com o MYSQL - JDBC

package bd;

import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/**
 *
 * @author KIKO
 */
public class insert {
    
    /** Creates a new instance of insert */
    public insert() {
    }
    public static void insere(String sql) throws SQLException{
         try {
            banco.init();
            Connection conn = banco.getConnection();
            Statement stat = conn.createStatement();
            stat.execute(sql);
            conn.close();
            stat.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
    }
}

public class UsuarioDAO{

    public void inserir(List<Usuario> usuarios) throws SQLException {
         try {
            banco.init();
            Connection conn = banco.getConnection();
            PreparedStatement stmt = conn.prepareStatement("INSERT INTO usuario(nome, login, senha) VALUES (?, ?, ?)");

            for(Usuario usu : usuarios){
               stmt.clearParameters();
               stmt.setString(1, usu.getNome());
               stmt.setString(2, usu.getLogin());
               stmt.setString(3, usu.getSenha());
               stmt.executeUpdate();
            }
            conn.close();
            stat.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
    }
}

public static void insere(String sql, Connection conn) {
  //sua implementaçao
}

//voce usaria assim:
Connection conn = //pega conexao
for(...) { //faz seu loop
  insere(suasql, conn);
}