Question

我有两个整数;开始和停止
最初启动为0，停止为1.一旦用户关闭窗口，启动就变为1。

我有一个更新我的JTable的方法;

private void Update_table(){


 try{
   String sql ="select * from orders  ";
   pst=conn.prepareStatement(sql);
   rs=pst.executeQuery();
   Table_Employee.setModel(DbUtils.resultSetToTableModel(rs));


 }
 catch(Exception e){
   JOptionPane.showMessageDialog(null, e);

 }

}

我想连续更新表，但是当我在void main方法中放入while循环时程序崩溃;

void main;

public static void main(String args[]) {
    /* Set the Nimbus look and feel */

            //Update_table();
  while(start<stop)
      new Employee_info().Update_table();


    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(Employee_info.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(Employee_info.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(Employee_info.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(Employee_info.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new Employee_info().setVisible(true);
         //   while(1<2)
           // rh.Update_table();
           // Update_table();
        }
    });
}

错误;

com.mysql.jdbc.exceptions.jdbc4.MySQL SyntaxErrorException: User 12345 already has more than 'max_user_connections' active connections

其中12345是连接数据库的用户名，是因为我在不同的类中登录数据库并运行查询？

连接类;

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

public class javaconnect {
Connection conn=null;

    public static Connection ConnecrDb(){
      try{
      Class.forName("com.mysql.jdbc.Driver");
      Connection conn = DriverManager.getConnection("jdbc:mysql://XXX.com:3306/XXX_pizza","12345 ","XXXX");
    //  JOptionPane.showMessageDialog(null, "You got connected");
              return conn;

    }catch(ClassNotFoundException | SQLException e){
        JOptionPane.showMessageDialog(null, e);
        return null;
}      

}
}

Employee_Info类调用javaconnect类来建立连接;

public Employee_info() {
    initComponents();
    conn=javaconnect.ConnecrDb();
    Update_table();

}

Answer 1

有几件事：

1）在这样的while循环中，你应该在某个时候调用Thread.sleep（）。 2）在这种情况下，因为每次调用Employee_info构造函数时，您都没有睡觉并获得新连接，所以您创建了大量连接，这可能是导致错误的直接原因。 3）您不应该有像Employee_info这样的业务对象建立连接。相反，你应该在它们之间有一个层（通常称为数据访问层），如下所示：

public class EmployeeDao {

    public Employee_info getEmployeeInfo(){
        Connection conn = getConnection();
        //do something with the connection, construct employee info
        return employeeInfo
    }
}

4）您应该使用连接池，而不是手动实例化连接。 Commons-dbcp通常是一个二手的，呃。

5）遵循Java命名约定。

Main内部连续运行方法

1 个答案: