jdbc连接数据库得到列名和值，显示在JTable中出错，已经郁闷到内伤！

小弟近来学习jdbc，想把表的内容显示到JTable中，但是老是出问题，请大家帮帮我，看看我的代码哪里错了？谢谢！
下面是我写的代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;

import javax.swing.JFrame;

import javax.swing.JTable;
/**
* @author Administrator
*
* TODO 要更改此生成的类型注释的模板，请转至
* 窗口 － 首选项 － Java － 代码样式 － 代码模板
*/
public class JTableTest extends JFrame {

private javax.swing.JPanel jContentPane = null;
private JTable jTable = null;
String[] columnNames=null;

Object[][] data=null;

/**
* This method initializes jTable
*
* @return javax.swing.JTable
*/
// private JTable getJTable() {
// if (jTable == null) {
// jTable = new JTable(data,columnNames);
// }
// return jTable;
// }
public static void main(String[] args) throws Exception {
JTableTest t=new JTableTest();
t.show();
System.out.println("ooookkkkkkk");
}
/**
* This is the default constructor
* @throws Exception
*/
public JTableTest() throws Exception {

initialize();
}
/**
* This method initializes this
*
* @return void
* @throws Exception
*/
private void initialize() throws Exception {

Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
String url="jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=pubs";
Connection con=DriverManager.getConnection(url,"sa","sa");
Statement stmt=con.createStatement();
ResultSet rs=stmt.executeQuery("select * from authors");
ResultSetMetaData rsm=rs.getMetaData();
for(int i=1;i<rsm.getColumnCount();i++)
{
columnNames[i-1]=rsm.getColumnName(i);
}
//while(rs.next())
for(int j=1;j<rs.getRow();j++)
{
for(int i=1;i<rsm.getColumnCount();i++)
{
data[j-1][i-1]=rs.getObject(i);
}
}
rs.close();
stmt.close();
con.close();

jTable = new JTable(data,columnNames);
this.setContentPane(jTable);
this.setSize(676, 383);
this.setTitle("JFrame");
}
/**
* This method initializes jContentPane
*
* @return javax.swing.JPanel
*/
private javax.swing.JPanel getJContentPane() {
if(jContentPane == null) {
jContentPane = new javax.swing.JPanel();
jContentPane.setLayout(new java.awt.BorderLayout());
}
return jContentPane;
}
} // @jve:decl-index=0:visual-constraint="92,25"

我感觉我自己的写的代码没错了，但是运行的时候就是报错，以下是报错的内容：

java.lang.NullPointerException
at j2ee_bean.JTableTest.initialize(JTableTest.java:73)
at j2ee_bean.JTableTest.<init>(JTableTest.java:55)
at j2ee_bean.JTableTest.main(JTableTest.java:45)
Exception in thread "main"

唉，郁闷呀！