Java idea 连接sqlserver服务器失败

按照网上教程添加驱动后程序运行错误
显示如下：

img


package geng.handle; 
import geng.model.Register;
import java.sql.*;
import javax.swing.JOptionPane;
public class HandleInsertData {
   Connection con;
   PreparedStatement preSql;  
   public HandleInsertData(){
      try{  Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");//加载JDBC-MySQL驱动
      }
      catch(Exception e){}
      String 
      uri = "jdbc:sqlserver://localhost:1433;DatabaseName=test";
      try{  
         con = DriverManager.getConnection(uri,"sa","123456"); //连接代码
          System.out.println("服务器连接成功！");
      }
      catch(SQLException e){}

   }
   public void writeRegisterModel(Register register) {
      String sqlStr ="insert into register values(?,?,?)";
      int ok = 0;
      try { 
          preSql = con.prepareStatement(sqlStr);
          preSql.setString(1,register.getID());       
          preSql.setString(2,register.getPassword());  
          preSql.setString(3,register.getBirth());
          ok = preSql.executeUpdate();
          con.close();
      }
      catch(SQLException e) {
         JOptionPane.showMessageDialog(null,"id不能重复","警告",
                                   JOptionPane.WARNING_MESSAGE);
      }
      if(ok!=0) {
         JOptionPane.showMessageDialog(null,"注册成功",
                             "恭喜",JOptionPane.WARNING_MESSAGE);
      }
   }
}

参考教程：https://blog.csdn.net/HHeyanjie/article/details/114936560

main方法没有么，创建con 的方法没调用，con 为空了吧