Question

Good night all, this is my first question.

i got some problem when running ZK application with tomcat webserver

java.lang.ClassCastException: org.postgresql.jdbc4.Jdbc4Connection cannot be cast to controller.connection
controller.connection.(connection.java:27)
controller.lap_keuangan.lk_Controller.preparelistlk(lk_Controller.java:34)
controller.lap_keuangan.lk_Controller.doAfterCompose(lk_Controller.java:30)

this is my connection class:

package controller;

//import ommited


public class connection {

  private static final String url="jdbc:postgresql://192.168.56.101:5432/adempiere";
  private static final String user = "postgres";
  private static final String pwd = "auliaardy";
  private connection conn;

  public connection()throws Exception{
      try {
          DriverManager.registerDriver(new org.postgresql.Driver());
          conn =  (connection) DriverManager.getConnection(url,user,pwd);

      } catch (SQLException e) {
          System.out.println("Driver tidak ditemukan"+e);
      }
  }

  public Connection getConnection(){
      return (Connection) conn;
  }

  public void closeConnection(){
      try {
          conn.closeConnection();
      } catch (Exception e) {
          System.out.println("gagal menutup koneksi disebabkan: "+e);
      }
  }

  }

and this is my controller class

//import ommited here

public class lk_Controller extends GenericForwardComposer {

    private Listbox listlk;

    @Override
    public void doAfterCompose(Component comp) throws Exception {
        super.doAfterCompose(comp);
        preparelistlk();
    }

    public void preparelistlk() throws Exception {
        connection c = new connection();
        try {
            l_keuangan lk = new l_keuangan(c.getConnection());
            List<tbl_lk> llk = lk.getLKeuangan();
            ListModelList lml = new ListModelList(llk, true);
            listlk.setModel(lml);
            listlk.setItemRenderer(new ListitemRenderer() {

                @Override
                public void render(Listitem lslk, Object o) throws Exception {

                    try {

                        tbl_lk tl = (tbl_lk) o;
                        new Listcell(ubahtanggal()).setParent(lslk);
                        new Listcell(Integer.toString(tl.getSum_debit())).setParent(lslk);
                        new Listcell(Integer.toString(tl.getSum_credit())).setParent(lslk);
                        new Listcell(Integer.toString(tl.getTotal())).setParent(lslk);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public  String ubahtanggal() {
        tbl_lk lk = new tbl_lk();
        DateFormat df = new SimpleDateFormat("YYYY/MM/DD");
        long tanggal = lk.getTanggal().getTime();
        String tgl = df.format(tanggal);
        return tgl;




    }
}

tomcat said error at line:
DriverManager.registerDriver(new org.postgresql.Driver());
conn = (connection) DriverManager.getConnection(url,user,pwd);

i cant changed the cast connection to:
conn = DriverManager.getConnection(url,user,pwd);

please somebody help, i got stuck over night T.T

Answer 1

The DriverManager object returns an implementation of java.sql.Connection. It won’t return an instance of your controller.connection class. Your conn variable should be of type java.sql.Connection.

Note that:

• classes in Java, by convention, always start with an upper-case letter
• naming your class connection, and make it wrap an object of class Connection, is really really confusing. So confusing that you got confused by your own code.