如何显示从mysql到jtext field的空白数据

Question

我制作了一个java程序，其中sql表将绑定到jtable。问题是，当我在具有空/空数据的jtable上单击行时，该行的下一列将不会显示在textfield上。如果空白数据位于第4列，则文本字段将仅显示第1到第3列的数据，而将下一个文本字段留空。显示的错误也是线程“AWT-EventQueue-0”java中的异常。lang.NullPointerException。我正在为这个程序使用这个示例数据库https://www.mysqltutorial.org/wp-content/uploads/2018/03/mysqlsampledatabase.zip

package test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.JOptionPane;
import javax.swing.table.DefaultTableModel;

/**
 *
 * @author User1
 */
public class frmCustomers extends javax.swing.JInternalFrame {

/**
 * Creates new form frmCustomers
 */
private int selectedRow;
private int totalrow;
private int row;


public frmCustomers() {
    initComponents();
    BINDDATA();
    row = 0;
    
    
    btnPrevious.setEnabled(false);
    btnFirst.setEnabled(false);
    btnNext.setEnabled(true);
    btnLast.setEnabled(true);

}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {
    pack();
}// </editor-fold>                        

private void btnDisplayActionPerformed(java.awt.event.ActionEvent evt) {                                           
    BINDDATA();        
}                                          

private void btnFirstActionPerformed(java.awt.event.ActionEvent evt) {                                         
    
}                                        

private void btnNextActionPerformed(java.awt.event.ActionEvent evt) {                                        
    
}                                       

private void btnPreviousActionPerformed(java.awt.event.ActionEvent evt) {                                            
    
}                                           

private void btnLastActionPerformed(java.awt.event.ActionEvent evt) {                                        
    
}                                       

private void btnInsertActionPerformed(java.awt.event.ActionEvent evt) {                                          
    INSERT();
    BINDDATA();
}                                         

private void btnUpdateActionPerformed(java.awt.event.ActionEvent evt) {                                          
    UPDATE();  
    BINDDATA();
}                                         

private void btnDeleteActionPerformed(java.awt.event.ActionEvent evt) {                                          
    DELETE();
    BINDDATA();
}                                         

private void tblCustomersMouseClicked(java.awt.event.MouseEvent evt) {                                          
    DefaultTableModel table = (DefaultTableModel) tblCustomers.getModel();
    selectedRow = tblCustomers.getSelectedRow();
    
    txtCustomerNumber.setText(table.getValueAt(selectedRow, 0).toString());
    txtCustomerName.setText(table.getValueAt(selectedRow, 1).toString());
    txtContactLastName.setText(table.getValueAt(selectedRow, 2).toString());
    txtContactFirstName.setText(table.getValueAt(selectedRow, 3).toString());
    txtPhone.setText(table.getValueAt(selectedRow, 4).toString());
    txtAddressLine1.setText(table.getValueAt(selectedRow, 5).toString());
    txtAddressLine2.setText(table.getValueAt(selectedRow, 6).toString());
    txtCity.setText(table.getValueAt(selectedRow, 7).toString());
    txtState.setText(table.getValueAt(selectedRow, 8).toString());
    txtPostalCode.setText(table.getValueAt(selectedRow, 9).toString());
    jComboBox1.setSelectedItem(table.getValueAt(selectedRow, 10).toString());
    txtSalesRep.setText(table.getValueAt(selectedRow, 11).toString());
    txtCreditLimit.setText(table.getValueAt(selectedRow, 12).toString());
}                                         

public void INSERT() {
    try  {
        PreparedStatement pst;
        
        String number = txtCustomerNumber.getText().trim();
        String name = txtCustomerName.getText().trim();
        String last = txtContactLastName.getText().trim();
        String first = txtContactFirstName.getText().trim();
        String phone = txtPhone.getText().trim();
        String address1 = txtAddressLine1.getText().trim();
        String address2 = txtAddressLine2.getText().trim();
        String city = txtCity.getText().trim();
        String state = txtState.getText().trim();
        String postal = txtPostalCode.getText().trim();
        String country = (String) jComboBox1.getSelectedItem();
        String salesrep = txtSalesRep.getText().trim();
        String creditlim = txtCreditLimit.getText().trim();
        
        Class.forName("com.mysql.cj.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels",
                "root","passweird");
        
        String sql = "INSERT INTO customers values (?,?,?,?,?,?,?,?,?,?,?,?,?)";
        pst = con.prepareStatement(sql);
        pst.setString(1, number);
        pst.setString(2, name);
        pst.setString(3, last);
        pst.setString(4, first);
        pst.setString(5, phone);
        pst.setString(6, address1);
        pst.setString(7, address2);
        pst.setString(8, city);
        pst.setString(9, state);
        pst.setString(10, postal);
        pst.setString(11, country);
        pst.setString(12, salesrep);
        pst.setString(13, creditlim);
        
        pst.execute();
        
     con.close();
    }
    catch (Exception e)
    {
        JOptionPane.showMessageDialog(null, "Error establishing connection!!!" + e.toString());
    }    
}
private void UPDATE(){
    try {
        String number = txtCustomerNumber.getText().trim();
        String name = txtCustomerName.getText().trim();
        String last = txtContactLastName.getText().trim();
        String first = txtContactFirstName.getText().trim();
        String phone = txtPhone.getText().trim();
        String address1 = txtAddressLine1.getText().trim();
        String address2 = txtAddressLine2.getText().trim();
        String city = txtCity.getText().trim();
        String state = txtState.getText().trim();
        String postal = txtPostalCode.getText().trim();
        String country = (String) jComboBox1.getSelectedItem();
        String salesrep = txtSalesRep.getText().trim();
        String creditlim = txtCreditLimit.getText().trim();
         
        Class.forName("com.mysql.cj.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels",
                "root","passweird");
        
        Statement st = con.createStatement();
        
        String sql = "UPDATE customers set customerNumber='" + number + "', customerName='" + name
                + "', contactLastName='" + last + "', contactFirstName='" + first + "', phone='" + phone
                + "', addressLine1='" + address1 + "', adressLine2='" + address2 + "', city='" + city
                + "', state='" + state + "', postalCode='" + postal + "', country='" + country 
                + "', salesRepEmployeeNumber='" + salesrep + "', creditLimit='" + creditlim;
        
        int result = st.executeUpdate(sql);
        
        if(result > 0) {
            JOptionPane.showMessageDialog(null, "You have successfully updated the record!!!");
        }
    }
    catch (Exception e) {
    }
}
private void DELETE(){
    try{
        String number = txtCustomerNumber.getText().trim();
        Class.forName("com.mysql.cj.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels",
                "root","passweird");
        
        Statement st = con.createStatement();
        String sql = " DELETE FROM customers WHERE customerNumber = " + number;
        
        int result = st.executeUpdate(sql);
        
        if (result > 0){
            JOptionPane.showMessageDialog(null, "You have successfully deleted the record!!!");
        }
    }
        catch (Exception e){
    }
}
private void BINDDATA(){
    try {
        Class.forName("com.mysql.cj.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels",
                "root","passweird");
        
        Statement st = con.createStatement();
        String sql = "SELECT * FROM customers";
        ResultSet rs = st.executeQuery(sql);
        
        DefaultTableModel table = (DefaultTableModel) tblCustomers.getModel();
        table.setRowCount(0);
        
        while(rs.next()) {
            Object obj[] = {rs.getInt("customerNumber"), rs.getString("customerName"), rs.getString("contactLastName"), rs.getString("contactFirstName"),
                            rs.getString("phone"), rs.getString("addressLine1"), rs.getString("addressLine2"),
                            rs.getString("city"), rs.getString("state"), rs.getString("postalCode"), rs.getString("country"),
                            rs.getInt("salesRepEmployeeNumber"), rs.getObject("creditLimit"),};
                table.addRow(obj); 
                
            }
            con.close();
            
            totalrow = table.getRowCount();
        }
    catch (Exception e) {
    }
}

// Variables declaration - do not modify                     
private javax.swing.JButton btnDelete;
private javax.swing.JButton btnDisplay;
private javax.swing.JButton btnFirst;
private javax.swing.JButton btnInsert;
private javax.swing.JButton btnLast;
private javax.swing.JButton btnNext;
private javax.swing.JButton btnPrevious;
private javax.swing.JButton btnUpdate;
private javax.swing.JComboBox<String> jComboBox1;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel10;
private javax.swing.JLabel jLabel11;
private javax.swing.JLabel jLabel12;
private javax.swing.JLabel jLabel13;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JLabel jLabel5;
private javax.swing.JLabel jLabel6;
private javax.swing.JLabel jLabel7;
private javax.swing.JLabel jLabel8;
private javax.swing.JLabel jLabel9;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTable tblCustomers;
private javax.swing.JTextField txtAddressLine1;
private javax.swing.JTextField txtAddressLine2;
private javax.swing.JTextField txtCity;
private javax.swing.JTextField txtContactFirstName;
private javax.swing.JTextField txtContactLastName;
private javax.swing.JTextField txtCreditLimit;
private javax.swing.JTextField txtCustomerName;
private javax.swing.JTextField txtCustomerNumber;
private javax.swing.JTextField txtPhone;
private javax.swing.JTextField txtPostalCode;
private javax.swing.JTextField txtSalesRep;
private javax.swing.JTextField txtState;
// End of variables declaration                   
}

Answer 1

检查您是否从数据库中获得了null，如果是，请在表的相关字段中输入一个空字符串。