如何将 sql 查询的结果导入 JTable？

Question

I am trying to import the results from an SQL query into a JTable, but when I run it, it tells me that the ResultSet object has no set row? What does this mean? how Can I fix this? here is what I've tried:

import javax.swing.*;
import java.sql.*;


public class GUI {


    // frame
    JFrame f;
    // Table
    JTable j;

    // Constructor
    GUI()
    {
        ResultSet result;
        // Frame initiallization
        f = new JFrame();

        // Frame Title
        f.setTitle("SQL to JTable");
        try{
            String dbURL = "jdbc:sqlserver://DESKTOP-TSKUNOE\\MSSQLSERVER:1433;databaseName=LMD";
            String user = "programer151";
            String password = "abhinav@123";
            Connection connection = DriverManager.getConnection(dbURL, user, password);
            String code = "select * from dbo.LMD_Table where [DATE] = '2019-02-01'";
            Statement statement = connection.createStatement();
            result = statement.executeQuery(code);

            // Data to be displayed in the JTable
            double[] data =
                    {result.getFloat(2), result.getFloat(3), result.getFloat(4), result.getFloat(5), result.getFloat(6), result.getFloat(7), result.getFloat(8), result.getFloat(9), result.getFloat(10), result.getFloat(11), result.getFloat(12), result.getFloat(13)};
            ;
            String[][] data1 = new String[13][0];

            for (int i = 0; i<=13; i++) {
                data1[i][0] = String.valueOf(data[i]);
            }
            String[] columnNames = {  "data", "data","data", "data", "data","data", "data", "data","data", "data", "data","data" };
            j = new JTable(data1,columnNames);
            j.setBounds(30, 40, 200, 300);

            // adding it to JScrollPane
            JScrollPane sp = new JScrollPane(j);
            f.add(sp);
            // Frame Size
            f.setSize(500, 200);
            // Frame Visible = true
            f.setVisible(true);

        }catch (SQLException e){
            e.printStackTrace();
        }
    }

    // Driver method
    public static void main(String[] args)
    {
        new GUI();
    }
}

the output I want is a JTable which gives me the results of an sql query

Answer 1

a null pointer exception is usually something that isn't getting initialized with a value and getting a null instead. Try adding breakpoints to check where that null is and once found add:

if (variable != null) { //variable could be an object

   //some code

}

Answer 2

the ResultSet object has no set row?

result = statement.executeQuery(code);
double[] data = {result.getFloat(2), result.getFloat(3), ...};

You can't just access a row in the ResultSet directly. You first need to point to a row in the Result set.

This is done by invoking the next() method of the ResultSet .

Then typically you would use looping code to read each row of data in the ResultSet :

result = statement.executeQuery(code);

while (result.next())
{
    // get the data from the current row of the ResultSet 
}

See: How to get a DefaultTableModel object's data into a subclass of DefaultTableModel for a more complete example of how to create your DefaultTableModel from a ResultSet.

Also, you should use a PreparedStatement to build the SQL query. It will allow you to more easily set the parameters of the query. Search the forum for more information and example code.