Question

我试图从我的jFrame表单中保存一些字段但是当我单击保存按钮时，我得到空指针异常。以前我得到的错误是文本字段不能为空所以我取消选中不是null但它不起作用，我决定不在MySQL插入语句中包含Voucher_no，因为它是一个自动增量，其文本字段不可编辑我的代码有问题吗？我正在使用Mysql Workbench。

try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/canning?zeroDateTimeBehavior=convertToNull", "root", "");
            con.setAutoCommit(false);
            try {

//            String kb = jTextField3.getText(); //voucher_no
                String kc = (String) jComboBox3.getSelectedItem(); //factory
                String kg = jTextField10.getText(); //fuel
                Double ks = Double.valueOf(kg);
                String ke = jTextField11.getText(); //electricity
                Double kt = Double.valueOf(ke);
                String kf = jTextField12.getText(); //manpower
                Double ku = Double.valueOf(kf);
                String kj = (String) jComboBox4.getSelectedItem();  //can_name
                String kk = (String) jComboBox5.getSelectedItem(); //label name
                String kq = jTextField23.getText();//no_of_cans
                Double kv = Double.valueOf(kq);
                String kr = jTextField24.getText();//no_of_labels
                Double kw = Double.valueOf(kr);

                String query1= "insert into production (date,factory,fuel,electricity,manpower,can_name,label_name,no_of_cans,no_of_labels)"
                        + "values (?,?,?,?,?,?,?,?,?)";

                try (PreparedStatement pst = con.prepareStatement(query1)){
//                    pst.setString(10, kb);
                    pst.setString(1, ((JTextField) jDate1.getDateEditor().getUiComponent()).getText());
                    pst.setString(2, kc);
                    pst.setDouble(3, ks);
                    pst.setDouble(4, kt);
                    pst.setDouble(5, ku);
                    pst.setString(6, kj);
                    pst.setString(7, kk);
                    pst.setDouble(8, kv);
                    pst.setDouble(9, kw);

                    pst.execute();
                }


            try {
                        int rows = jTable2.getRowCount();

                        for (int row = 0; row < rows; row++) {
                            String kd = (String) jTable2.getValueAt(row, 0);
                            Double kn = (Double) jTable2.getValueAt(row, 1);
                            try {
//                        Class.forName("com.mysql.jdbc.Driver").newInstance();
//                Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/canning?zeroDateTimeBehavior=convertToNull", "root", "");

                                String query = "insert into production(product_name,product_quantity)"
                                        + "values (?,?)";
                                PreparedStatement update = con.prepareStatement(query);
                                update.setString(1, kd);
                                update.setDouble(2, kn);

                                update.addBatch();

                                update.executeBatch();
                                con.commit();

                            } catch (SQLException e) {
                                e.printStackTrace();
//                        JOptionPane.showMessageDialog(this, "Error in production Table");
                            }
                        }
                    } catch (Exception e) {
                        JOptionPane.showMessageDialog(this, "Invalid Entry in fields");
                    }

            } catch (Exception e) {
                e.printStackTrace();
//                JOptionPane.showMessageDialog(null, "Invalid in fields");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

Answer 1

代码正在执行

                           update.addBatch();

                           update.executeBatch();
                           con.commit();

executeBatch和commit必须在循环外完成。误解源于＆＃34; addBatch＆＃34;应该已经命名为＆＃34; addToBatch。＆＃34;

Answer 2

尝试这样做。首先创建一个连接类，如下所示;

    import java.sql.Connection;
import java.sql.DriverManager;

 public class db_connection
 {
  public Connection connection()
    throws Exception
  {
    try
    {
       Connection conn = null;

      String username = "root"; String password = "";
      String driver = "com.mysql.jdbc.Driver";
      String url = "jdbc:mysql://localhost:3306/database";
       try {
         Class.forName(driver);
       } catch (Exception e) {
         e.printStackTrace();
         return null;
     }

       conn = DriverManager.getConnection(url, username, password);

       conn.setAutoCommit(false);
       return conn;
     } catch (Exception e) {
      e.printStackTrace();
      System.exit(0);
     }return null;
   }
 }

然后在你的保存按钮上执行类似的操作，

    private void ButtonRegGroup_SubmitActionPerformed(java.awt.event.ActionEvent evt) {                                                      
// TODO add your handling code here:
    if ((this.jTextFieldGrp_ReqAmnt.getText().equals(""))
            || (this.jTextFieldGrp_name.getText().equals(""))
            || (this.jTextFieldGrp_Id.getText().equals(""))
            || (this.jTextFieldGrp_prj_name.getText().equals(""))) {
        JOptionPane.showMessageDialog(this, "Some fields are empty", this.title, this.error);
    } else {
        try {
            this.con = ((Connection) new db_connection().connection());
            this.pst = ((PreparedStatement) this.con.prepareStatement("insert into registered_projects(project_type,name,project_name,project_id,constituency,ward,requested_amount)values(?,?,?,?,?,?,?)"));

            GroupRegDetails();
            this.pst.setString(1, this.proj_type);
            this.pst.setString(2, this.group_name);
            this.pst.setString(3, this.proj_name);
            this.pst.setInt(4, this.proj_id);
            this.pst.setString(5, this.constituency);
            this.pst.setString(6, this.ward);
            this.pst.setInt(7, this.requested_amount);
            int row = this.pst.executeUpdate();
            con.commit();
            if (row == 0) {
                this.con.rollback();
                JOptionPane.showInternalMessageDialog(this, "Didn't Register project", this.title, this.error);
            }
            JOptionPane.showMessageDialog(this, "Project Successfully Registered", this.title, this.infor);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
} 
 public void GroupRegDetails() {
     this.group_name = this.jTextFieldGrp_name.getText();
     this.proj_id = Integer.parseInt(this.jTextFieldGrp_Id.getText());
     this.proj_name = this.jTextFieldGrp_prj_name.getText();
     this.constituency = this.jComboBoxGrp_Comb_const.getSelectedItem().toString();
     this.ward = this.jComboBoxGrp_comb_Ward.getSelectedItem().toString();
     this.requested_amount = Integer.parseInt(this.jTextFieldGrp_ReqAmnt.getText());
     this.proj_type = "Group";
}

最后一个好的做法是将字段放在Jpanel和Jpanel上的Jpanel上。希望这会有所帮助。

jFrame字段未保存到db

2 个答案: