java - JDBC ResultSet.getString 在结果集异常开始/结束之前/之后

Question

我已经通过 Google 对这个主题进行了大量搜索，但我还没有找到以我使用它的方式使用 getString() 的人，所以我无法以正常的方式解决这个问题建议。

我想做的是从数据库中获取所有信息，然后使用它来填充程序中的表模型。为此，我使用 getString 获取数据并将其放入 String[] 对象中。这是我的 MySQLConnection 类:

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

public class MySQLConnect
{
    public MySQLConnect()
    {
        connect = null;
        statement = null;
        rSet = null;    
    }

    public void Connect(String dbase, String uname, String pword)
    {
        try
        {
            Class.forName("com.mysql.jdbc.Driver");

            connect = DriverManager.getConnection("jdbc:mysql://localhost/" + dbase , uname, pword);
            JOptionPane.showMessageDialog(null, "Connection successful.  Please retry your submission." , "Information", JOptionPane.INFORMATION_MESSAGE);          
        }

        catch (Exception e)
        {
            JOptionPane.showMessageDialog(null, e , "SQL Error", JOptionPane.ERROR_MESSAGE);
        }       
    }

    public void addDonor(int did, String dname, String dcname, int damount, DefaultTableModel model)
    {
        try
        {
            statement = connect.createStatement();

            statement.execute("Insert Into prg421_w5.donors Values ("+ did + ",'" + dname + "','" + dcname + "'," + damount + ")");
            JOptionPane.showMessageDialog(null, "Data entry added successfully." , "Information", JOptionPane.INFORMATION_MESSAGE);
            getRSet();
            updateTable(model);
        }

        catch (Exception e)
        {
            JOptionPane.showMessageDialog(null, e , "SQL Error", JOptionPane.ERROR_MESSAGE);
        }
    }

    public void getRSet()
    {
        try 
        {
            rSet = statement.executeQuery("Select * From donors");
        }

        catch (Exception e)
        {

        }
    }

    public void updateTable (DefaultTableModel model)
    {
        try
        {
            for (i = getRowCount(); i > 0; i--)
            {
                model.removeRow(0);
            }
        }

        catch (Exception e)
        {
            JOptionPane.showMessageDialog(null, e , "SQL Error", JOptionPane.ERROR_MESSAGE);
        }

        try
        {
            while (rSet.next())
            {
                String row[] = {rSet.getString("DonorName"),rSet.getString("DonorCharity"),((String)rSet.getString("DonationAmount"))};

                model.addRow(row);      
            }
        }

        catch (Exception e)
        {
            JOptionPane.showMessageDialog(null, e , "SQL Error", JOptionPane.ERROR_MESSAGE);
        }       
    }

    public int getRowCount()
    {
        try
        {
            rowCount = rSet.getInt(1);
        }

        catch (Exception e)
        {
            JOptionPane.showMessageDialog(null, e , "SQL Error", JOptionPane.ERROR_MESSAGE);
        }

        return rowCount;
    }   

    public Boolean isConnected()
    {
        return connect != null;
    }

    public void Close()
    {
        try
        {
          if (rSet != null)
          {
              rSet.close();
          }

          if (statement != null)
          {
              statement.close();
          }

          if (connect != null)
          {
              connect.close();
          }
        }

        catch (Exception e)
        {
            JOptionPane.showMessageDialog(null, e , "SQL Error", JOptionPane.ERROR_MESSAGE);
        }
    }


    private Connection connect;
    private Statement statement;
    private ResultSet rSet;
    private int rowCount, i;

    private static Object o = null;
}

但是我总是收到一条对话框错误消息，在标题中说明这些错误消息:

异常:在结果集开始之前

异常:结果集结束后

这里是堆栈跟踪:

java.sql.SQLException: Before start of result set at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1074) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:988) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:974) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:919) at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:854) at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2709) at MySQLConnect.getRowCount(MySQLConnect.java:100) at MySQLConnect.updateTable(MySQLConnect.java:68) at MySQLConnect.addDonor(MySQLConnect.java:42) at Operations.addDonor(Operations.java:135) at GUI$EventHandler.actionPerformed(GUI.java:145) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$200(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)

java.sql.SQLException: After end of result set at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1074) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:988) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:974) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:919) at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:854) at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2709) at MySQLConnect.getRowCount(MySQLConnect.java:100) at MySQLConnect.updateTable(MySQLConnect.java:68) at Operations.updateTable(Operations.java:164) at GUI$EventHandler.actionPerformed(GUI.java:148) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$200(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)

错误实际上是由 rSet.getInt(1) 产生的；在我的 getRowCount() 方法中。

数据仍在添加并且一切正常，但不得不关闭这些消息窗口只是令人讨厌。有人有什么建议吗？

Answer 1

在获取结果之前，您需要在 getRowCount() 中调用 rSet.next()(我什至不认为您会在此代码中的任何位置创建行计数查询)。

此外，您在丢弃数据库资源之前没有关闭它们，这将导致资源泄漏。 始终在您使用完数据库资源后立即在 finally block 中关闭它们。