目錄資源管理器獲取NPE

Question

以下代碼是FileTreeModel的修改版本，僅顯示目錄。然而。我在嘗試訪問需要管理員權限的文件夾時收到空指針異常。一個例子可能看起來像

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at DirectoryExplorer$FileTreeModel.listDirectories(DirectoryExplorer.java:112) 
    at DirectoryExplorer$FileTreeModel.getChildCount(DirectoryExplorer.java:79) 
    at javax.swing.tree.VariableHeightLayoutCache$TreeStateNode.expand(Unknown Source) 
    at javax.swing.tree.VariableHeightLayoutCache$TreeStateNode.expand(Unknown Source) 
    at javax.swing.tree.VariableHeightLayoutCache.ensurePathIsExpanded(Unknown Source) 
    at javax.swing.tree.VariableHeightLayoutCache.setExpandedState(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI.updateExpandedDescendants(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI$Handler.treeExpanded(Unknown Source) 
    at javax.swing.JTree.fireTreeExpanded(Unknown Source) 
    at javax.swing.JTree.setExpandedState(Unknown Source) 
    at javax.swing.JTree.expandPath(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI.toggleExpandState(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI.handleExpandControlClick(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI.checkForClickInExpandControl(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI$Handler.handleSelection(Unknown Source) 
    at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressed(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$500(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.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) 

要設法限制這個我添加了一個論點，即只增加了可見的文件夾到JTree，但是，這並不趕上他們。有沒有辦法排除需要探索管理員權限的所有文件夾？

MCVE/SSCCE

import java.awt.GridLayout; 

import java.io.File; 

import java.util.Arrays; 
import java.util.ArrayList; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.JScrollPane; 
import javax.swing.JTree; 
import javax.swing.tree.TreeModel; 


@SuppressWarnings("serial") 
public class DirectoryExplorer extends JFrame { 
    private DirectoryExplorer() { 
     super("Directory Explorer"); 
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     setLayout(new GridLayout(1, 1)); 
     createPanel(); 
     pack(); 
     setVisible(true); 
    } 


    private void createPanel() { 
     JPanel panel = new JPanel(new GridLayout(1, 1)); 

     TreeModel model = new FileTreeModel(new File("C:/")); 
     JTree tree = new JTree(model); 
     tree.setShowsRootHandles(true); 
     tree.collapseRow(0); 

     panel.add(new JScrollPane(tree)); 
     getContentPane().add(panel); 
    } 

    public static void main(String[] args) { 
     new DirectoryExplorer(); 
    } 

    private static class FileTreeModel implements TreeModel { 

     private File root; 

     public FileTreeModel(File root) { 
      this.root = root; 
     } 

     @Override 
     public void addTreeModelListener(javax.swing.event.TreeModelListener l) { 
      //do nothing 
     } 

     @Override 
     public Object getChild(Object parent, int index) { 
      File f = (File) parent; 
      return listDirectories(f)[index]; 
     } 

     @Override 
     public int getChildCount(Object parent) { 
      File f = (File) parent; 
      if (!f.isDirectory()) { 
       return 0; 
      } else { 
       return listDirectories(f).length; 
      } 
     } 

     @Override 
     public int getIndexOfChild(Object parent, Object child) { 
      File par = (File) parent; 
      File ch = (File) child; 
      return Arrays.asList(listDirectories(par)).indexOf(ch); 
     } 

     @Override 
     public Object getRoot() { 
      return root; 
     } 

     @Override 
     public boolean isLeaf(Object node) { 
      return false; 
     } 

     @Override 
     public void removeTreeModelListener(javax.swing.event.TreeModelListener l) { 
      //do nothing 
     } 

     @Override 
     public void valueForPathChanged(javax.swing.tree.TreePath path, Object newValue) { 
      //do nothing 
     } 

     private File[] listDirectories(File path) { 
      ArrayList<File> arrayList = new ArrayList<File>(); 
      for(File temp : path.listFiles()) { 
       if(temp.isDirectory() && !temp.isHidden()) 
        arrayList.add(temp); 
      } 

      return arrayList.toArray(new File[0]); 
     } 
    } 
} 

Answer 1

File.listFiles()可以返回null如果給定文件是不是一個目錄或無法讀取。見JavaDoc。

if(temp.isDirectory() && !temp.isHidden() && temp.listFiles()!=null)