Question

部署ZK时出现了一些错误

Jan 16, 2012 5:00:59 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [zkLoader] in context with path [/ZK509App6] threw exception
java.lang.NullPointerException
    at controller.jurnal.JournalController.<init>(JournalController.java:39)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at java.lang.Class.newInstance0(Class.java:355)
    at java.lang.Class.newInstance(Class.java:308)

这是我的JournalController.java类

public class JournalController extends GenericForwardComposer {

    private Listbox listlk;
    private Datebox datebox;
    private koneksi k;
    private Connection c;
    private SimpleDateFormat sdf;
    private Button pilih;
    private Date dates;
    private jurnalDAO jd = new jurnalDAO(k.getConnection(), dates);


    public JournalController() {
    }

    public void onClick$pilih(Event e) throws Exception, SQLException {
        try {
            Date d = datebox.getValue();
            d = dates;
            ForwardEvent forwardEvt = (ForwardEvent) e;
            Listbox Listlk = (Listbox) forwardEvt.getOrigin().getTarget();
        } catch (Exception a) {
            a.printStackTrace();
        }
    }
    public List<Jurnal_tbl> getAllEvents() throws SQLException, Exception {

        return jd.getLKeuangan();
    }
}

（JournalController.java:39）的行是 private jurnalDAO jd = new jurnalDAO（k.getConnection（），dates）;

对于引用，

，这是DAO类

public class jurnalDAO {

    private Connection conn;
    private Date tanggal;

    public jurnalDAO(Connection conn, Date dates) {
        this.conn = conn;
        this.tanggal = dates;
    }


    public List<Jurnal_tbl> getLKeuangan() throws SQLException, Exception {
        PreparedStatement ps = null;

        try {
            List<Jurnal_tbl> llk = new ArrayList<Jurnal_tbl>();
            System.out.println("test1");


            String sql = "SELECT * from public.jurnal where tanggal = ?";
            ps = conn.prepareStatement(sql);
            ps.setDate(1, new java.sql.Date(tanggal.getTime()));
            System.out.println(ps.toString());;

            ResultSet rs = ps.executeQuery();
            Jurnal_tbl jt;
            while (rs.next()) {
                // llk.add(new Jurnal_tbl(rs.getString("kd_jurnal"), rs.getString("no_trans"), rs.getString("tanggal"), rs.getString("account"), rs.getString("descript"), rs.getString("dc"), rs.getDouble("amount"), rs.getString("no_item")));
                jt = new Jurnal_tbl();
                jt.setKode(rs.getString("kd_jurnal"));
                jt.setTransaksi(rs.getString("no_trans"));
                jt.setTanggal(rs.getString("tanggal"));
                jt.setAkun(rs.getString("akun"));
                jt.setDeskripsi(rs.getString("descript"));
                jt.setDC(rs.getString("dc"));
                jt.setAmount(rs.getDouble("amount"));
                jt.setItem(rs.getString("no_item"));
                llk.add(jt);
           }

            rs.close();
            return llk;
        } finally {
        }
    }
}

请帮帮我们T.T 这是我单身汉的最后一个项目：T.T

Answer 1

您正在呼叫k.getConnection()，但您从未初始化k，因此它的默认值为null。这必然会抛出NullPointerException。您期望它在哪个对象上调用getConnection()？

作为旁注，值得关注名称：

k是一个非常无意义的实例变量名称
你在“journal”和“jurnal”之间不一致
类型名称koneksi不遵循Java命名约定（大小写）
变量名Listlk不遵循Java命名约定（大小写）
类型名称Jurnal_tbl不遵循Java命名约定（下划线）

此外：

你几乎永远不会抓住Exception
您应该关闭finally块

（我没有对代码进行彻底的分析 - 这只是我最初的印象。）

控制器中的ZK java空指针异常

1 个答案: