mysql和java連接

我想連接java與mysql數據庫，但我得到一個空指針異常。mysql和java連接

注：我之前用這個方法，效果不錯

這是代碼：

public void OpenConnection() throws SQLException{ 
    try { 

     try { 
      Class.forName("com.mysql.jdbc.Driver"); 
      try { 
     con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/hema?" 
      + "user=root&password=hima27890"); 

      } catch (SQLException ex) { 
       System.out.print("Connection Not Found"); 
      } 

     } catch (ClassNotFoundException ex) { 
      System.out.print("Not found Class"); 
     } 
    } finally { 
     System.out.close(); 
    } 




}

，這是爲了在數據庫返回一些數據的方法：

 public String[] GetData(String website) throws ClassNotFoundException, SQLException{ 
//  System.out.println("\nGet data method"); 
//  System.out.println("connection will start now"); 
     OpenConnection(); 
     System.out.println("connection works"); 

     String queryget="SELECT * FROM hema.passwords WHERE website='"+website+"'"; 

     Statement stm=(Statement) con.createStatement(); 

     ResultSet rs; 
     rs = stm.executeQuery(queryget); 

     if(rs.next()){ 
     System.out.println("if works"); 
      arr[0]=rs.getString("email"); 
     arr[1]=rs.getString("username"); 
     arr[2]=rs.getString("password"); 

     } 
     else{ 

     System.out.println("The website doesn't exist"); 
     } 
     System.out.println("method done"); 
     return arr; 
    } 



}

我把一些System.out.print知道錯誤在哪裏，它們都是分叉的，但不是最後一個「方法完成」。

，這是在調用的最後一個方法的JForm的代碼：

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {           

    try { 
     String Website = jTextField1.getText(); 
     System.out.println("Website is "+Website); 
     Model model=new Model(); 
     String arr2[]=model.GetData(Website); 
     System.out.println("App"); 
     EmailText.setText(arr2[0]); 
     UserText.setText(arr2[1]); 
     PasswordText.setText(arr2[2]); 

    } catch (ClassNotFoundException ex) { 
     Logger.getLogger(Passwords.class.getName()).log(Level.SEVERE, null, ex); 
    } catch (SQLException ex) { 
     Logger.getLogger(Passwords.class.getName()).log(Level.SEVERE, null, ex); 
    } 





}

堆棧跟蹤：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
at Model.Model.GetData(Model.java:68) 
at View.Passwords.jButton1ActionPerformed(Passwords.java:161) 
at View.Passwords.access$200(Passwords.java:15) 
at View.Passwords$3.actionPerformed(Passwords.java:64) 
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022) 
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346) 
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) 
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) 
at java.awt.Component.processMouseEvent(Component.java:6527) 
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) 
at java.awt.Component.processEvent(Component.java:6292) 
at java.awt.Container.processEvent(Container.java:2234) 
at java.awt.Component.dispatchEventImpl(Component.java:4883) 
at java.awt.Container.dispatchEventImpl(Container.java:2292) 
at java.awt.Component.dispatchEvent(Component.java:4705) 
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898) 
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533) 
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462) 
at java.awt.Container.dispatchEventImpl(Container.java:2278) 
at java.awt.Window.dispatchEventImpl(Window.java:2739) 
at java.awt.Component.dispatchEvent(Component.java:4705) 
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746) 
at java.awt.EventQueue.access$400(EventQueue.java:97) 
at java.awt.EventQueue$3.run(EventQueue.java:697) 
at java.awt.EventQueue$3.run(EventQueue.java:691) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86) 
at java.awt.EventQueue$4.run(EventQueue.java:719) 
at java.awt.EventQueue$4.run(EventQueue.java:717) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75) 
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716) 
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) 
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) 
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

生成成功（總時間：21秒），

來源

2014-10-11 Ibrahim Keshek

注：我之前用這個方法，效果不錯 – 2014-10-11 03:53:58

可能重複：http://stackoverflow.com/questions/2591505/java-lang-classnotfoundexception-com-mysql-jdbc -driver – Nathan 2014-10-11 03:59:46

你有沒有添加mysql jar到你的項目？ – 2014-10-11 04:18:14

好的，我知道問題出在哪裏它是在代碼的開頭聲明array字符串，所以它沒有改變，當我使用d if語句，所以我用數組ArrayList<String>

來源

2014-10-11 05:02:57

mysql和java連接

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