java中连接数据库出问题不知道怎么解决
0
悬赏园豆：10
[已解决问题]
解决于 2015-01-13 13:48
package controller; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; import javax.swing.JOptionPane; import view.DengluWindow; import view.VoteWindow; import model.AllWin; public class OKButtonListener implements ActionListener{ @Override public void actionPerformed(ActionEvent e) { // TODO Auto-generated method stub //创建“VoteWindow窗体” //AllWin.voteWindow=new VoteWindow("这是投票的窗体！","tubiao.jpg","beijing.jpg"); String name=DengluWindow.userField.getText(); String mima=DengluWindow.passwordField.getText(); Connection con1; Statement st; ResultSet rs; if(name.equals("")||mima.equals(""))//如果没输用户名或密码,则提示对不起,请输入用户名或密码 { JOptionPane.showOptionDialog(null,"Error：用户名或者密码不能为空！","警告提示！", JOptionPane.DEFAULT_OPTION,JOptionPane.WARNING_MESSAGE,null,null,null); } else//如果都有数据了就开始连接数据库验证 { try { // 加载驱动程序 Class.forName("com.mysql.jdbc.Driver"); //建立连接 con1=(Connection) DriverManager.getConnection("jdbc:mysql://localhost/user","root","520520"); st=(Statement) con1.createStatement(); rs=((java.sql.Statement) st).executeQuery("select * from tb_user where username='"+name+"'"); if(rs.next())//如果存在,就验证密码 { if(rs.getString("pwd").equals(mima))//如果密码正确就提示,反之 { //隐藏登录窗体 AllWin.dengluWindow.setVisible(false); AllWin.dengluWindow.validate(); //创建“VoteWindow窗体” AllWin.voteWindow=new VoteWindow("这是投票的窗体！","tubiao.jpg","beijing.jpg"); } else { JOptionPane.showOptionDialog(null,"Error：密码错误！","警告提示！", JOptionPane.DEFAULT_OPTION,JOptionPane.WARNING_MESSAGE,null,null,null); } } else//如果没有查找到用户名就提示 { JOptionPane.showOptionDialog(null,"Error：没有此用户名！","警告提示！", JOptionPane.DEFAULT_OPTION,JOptionPane.WARNING_MESSAGE,null,null,null); } } catch (Exception e1) { // TODO Auto-generated catch block e1.printStackTrace(); } } } }
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at controller.OKButtonListener.actionPerformed(OKButtonListener.java:26) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236) at java.awt.Component.processMouseEvent(Component.java:6267) at javax.swing.JComponent.processMouseEvent(JComponent.java:3267) at java.awt.Component.processEvent(Component.java:6032) at java.awt.Container.processEvent(Container.java:2041) at java.awt.Component.dispatchEventImpl(Component.java:4630) at java.awt.Container.dispatchEventImpl(Container.java:2099) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168) at java.awt.Container.dispatchEventImpl(Container.java:2085) at java.awt.Window.dispatchEventImpl(Window.java:2478) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.EventQueue.dispatchEvent(EventQueue.java:599) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
就是有两个窗体，登陆和投票，登陆时有用户名和密码，点击提交按钮就进入到投票窗体。按钮有监听，就是这个监听有问题。我在数据库里建立了一张用户表，只要符合表里的用户名和密码就能登陆进入投票窗体。
最佳答案
0
出错信息是空指针异常，行号为26行，看你的代码极有可能出问题的地方在
//建立连接
con1=(Connection) DriverManager.getConnection("jdbc:mysql://localhost/user","root","520520");
st=(Statement) con1.createStatement();
rs=((java.sql.Statement) st).executeQuery("select * from tb_user where username='"+name+"'");
可断点检查con1,st,rs是否取到的为空
是否为数据库连接错误，getConnection("jdbc:mysql://localhost/user","root","520520");
收获园豆：10
谢谢啦
其他回答(1)
0
有个变量没有实例化或者取到的为空，在Eclipse Debug单步可直接调试
谢谢啦
