帮忙看个异常！

Question

这个异常有时出现，有时不出现，不知道是什么原因，希望大家能帮下忙Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.JComponent._paintImmediately(Unknown Source)
at javax.swing.JComponent.paintImmediately(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(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)

Answer 1

      public int i=0;
  public String filename;
  public String filePath = "";
  public String case_content;
  public JDBCUtil datebase;
  public DownLoad(List list,List namelist)
      {
       
       try { 
     datebase=JDBCUtil.getInstance();   
        setIconImage(Toolkit.getDefaultToolkit().createImage(getClass()
                     .getResource("/net/sf/xpontus/icons/icone.png")));
   JFileChooser choosers = new JFileChooser();//
   choosers.setDialogTitle("保存文件");
    FileNameExtensionFilter filter = new FileNameExtensionFilter("压缩文件(zip)","zip");//
    choosers.addChoosableFileFilter(filter);

    choosers.setFileFilter(filter);

    choosers.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);

    int returnVal = choosers.showSaveDialog(this);
   
    if(returnVal == JFileChooser.APPROVE_OPTION)
     filePath = choosers.getSelectedFile().getAbsolutePath();

    else{
        list.clear();
        namelist.clear();
        return;
    }
 
     //构建文件路径
    for(int j=0;j<list.size();j++)
    {
        ResultSet rs=datebase.executeQuery("SELECT * FROM UOF_TEST_CASE WHERE CASE_ID="+Integer.valueOf((String) list.get(j)));
        while(rs.next())
        {
         case_content=rs.getString("CASE_CONTENT");
        }
        if(case_content==null||case_content.equals(""))
        {
            JOptionPane.showMessageDialog(this,"该案例没有文件下载");
         return;
        }else
        {
        
         int cnt=0,start = 0;  
         int m=0;
         while(start!=filePath.length()){  
         m = filePath.indexOf("\\",start);  
         if(m!=-1)  
         {  
           cnt ++;  
           start = m+1;  
         }  
         else  
         break;  
         }  
//          System.out.println("start="+start);
//          System.out.println("cnt"+cnt);
                if(cnt==1&&filePath.length()<=start)
                {  
//                  System.out.println("this is"+filePath+namelist.get(j).toString()+".zip");
                 Thread th=new ThreadDownLoad(filePath+namelist.get(j).toString()+".zip", Integer.valueOf((String) list.get(j)));
                    th.start();
                    DefaultXPontusWindowImpl window = (DefaultXPontusWindowImpl) XPontusComponentsUtils.getTopComponent();
                    window.getDocumentTabContainer().createImageView("d:\\unzip\\"+namelist.get(j).toString()+"\\"+namelist.get(j).toString(),Integer.valueOf((String) list.get(j)));
                }else
                {
//                 System.out.println("this is "+filePath+"\\"+namelist.get(j).toString()+".zip");
                 Thread th=new ThreadDownLoad(filePath+"\\"+namelist.get(j).toString()+".zip", Integer.valueOf((String) list.get(j)));
                    th.start();
                    DefaultXPontusWindowImpl window = (DefaultXPontusWindowImpl) XPontusComponentsUtils.getTopComponent();
                    window.getDocumentTabContainer().createImageView("d:\\unzip\\"+namelist.get(j).toString()+"\\"+namelist.get(j).toString(),Integer.valueOf((String) list.get(j)));
                }
                
        
               
//      downloadNet(Integer.valueOf((String) list.get(j)),filePath+"//"+namelist.get(j).toString()+".zip");
        }
    }
    
     datebase.close();
     } catch (SQLException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
     } catch (Exception ef) {
// TODO Auto-generated catch block
ef.printStackTrace();
}
        list.clear();
        namelist.clear();
      }

Answer 2

swing只能调用特定用户线程，来产生多线程的。

Answer 3

有可能是这个问题，soli11722984　哪个代码是我修改过了，以前调用下个界面我是在线程里对文件解压后执行的，但是我想的就是并发事件不影响啊，因为我只调用了一次，而且也执行了一件事．

Answer 4

csdn 害死我了 居然找不到一个能不用流快速拷贝大文件的方法
是在没辙