pendrive的JAVA文件树模型速度较慢

Question

我正在开发一个应用程序，该应用程序将大量使用通过USB访问的外部存储器。我已经实现了用于浏览磁盘上目录的TreeModel。它适用于：

• Ubuntu上的本地光盘
• Ubuntu上连接的外部存储器
• Windows 7上的本地光盘

但在Windows7上连接外部存储器很糟糕，我不知道为什么。以pendrive作为根目录，用这个模型滚动JTree是非常麻烦的。一开始，我认为java.io.File中的listFiles()对于pendrive来说速度较慢，所以我在模型中添加了一些缓存，但它不起作用——滚动仍然很糟糕。

我刚刚注意到它与Look&感觉对于系统L&对于Nimbus L&F它没有那么糟糕，但仍然不完美。

FileTreeModel:

import java.io.File;
import java.io.FileFilter;
import java.io.Serializable;
import java.util.*;
import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreePath;
public class FileTreeModel implements TreeModel {
    private File root;
    private boolean onlyFolders;
    private boolean showHidden;
    private final Object LEAF = new Serializable() {
    };
    private Map<File, Object> map;
    private LinkedList<TreeModelListener> listeners = new LinkedList<>();
    private FileFilter directoryFilter = new FileFilter() {
        @Override
        public boolean accept(java.io.File pathname) {
            return pathname.isDirectory();
        }
    };
    public FileTreeModel(File root, boolean onlyFolders, boolean showHidden) {
        this.root = root;
        this.onlyFolders = onlyFolders;
        this.showHidden = showHidden;
        this.map = new HashMap();
    }
    public FileTreeModel() {
    }
    public boolean isShowHidden() {
        return showHidden;
    }
    public void setShowHidden(boolean showHidden) {
        this.showHidden = showHidden;
    }
    @Override
    public Object getRoot() {
        return root;
    }
    public void setRoot(File root) {
        Object oldRoot = this.root;
        this.root = root;
        map.clear();
        TreeModelEvent event = new TreeModelEvent(root, new Object[]{root});
        for (TreeModelListener listener : listeners) {
            listener.treeStructureChanged(event);
        }
    }
    @Override
    public boolean isLeaf(Object node) {
        return ((File) node).isFile();
    }
    @Override
    public int getChildCount(Object parent) {
        if (parent instanceof java.io.File && ((java.io.File) parent).canRead()) {
            List<File> files = children(parent);
            int result = 0;
            for (java.io.File file : files) {
                if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                        && ((!file.isHidden() && !showHidden) || showHidden)) {
                    result++;
                }
            }
            return result;
        }
        return 0;
    }
    @Override
    public Object getChild(Object parent, int index) {
        if (parent instanceof java.io.File) {
            List<File> files = children(parent);
            List<java.io.File> resultFiles = new LinkedList<>();
            for (java.io.File file : files) {
                if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                        && ((!file.isHidden() && !showHidden) || showHidden)) {
                    resultFiles.add(file);
                }
            }
            return resultFiles.get(index);
        }
        return null;
    }
    @Override
    public int getIndexOfChild(Object parent, Object child) {
        if (parent instanceof java.io.File) {
            List<File> files = children(parent);
            List<java.io.File> resultFiles = new LinkedList<>();
            for (java.io.File file : files) {
                if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                        && ((!file.isHidden() && !showHidden) || showHidden)) {
                    resultFiles.add(file);
                }
            }
            return resultFiles.indexOf(child);
        }
        return -1;
    }
    @Override
    public void valueForPathChanged(TreePath path, Object newvalue) {
    }
    @Override
    public void addTreeModelListener(TreeModelListener l) {
        listeners.add(l);
    }
    @Override
    public void removeTreeModelListener(TreeModelListener l) {
        listeners.remove(l);
    }
    //============================PRIVATE METHODS===============================
    protected List<File> children(Object node) {
        File f = (File) node;
        Object value = map.get(f);
        if (value == LEAF) {
            return null;
        }
        List children = (List) value;
        if (children == null) {
            File[] c = f.listFiles();
            if (c != null) {
                children = new ArrayList(c.length);
                for (int len = c.length, i = 0; i < len; i++) {
                    children.add(c[i]);
                    if (!c[i].isDirectory()) {
                        map.put(c[i], LEAF);
                    }
                }
            } else {
                children = new ArrayList(0);
            }
            map.put(f, children);
        }
        return children;
    }
}

样品形式：

import folderlist.model.treemodels.FileTreeModel;
import java.io.File;
import java.util.Vector;
import javax.swing.DefaultComboBoxModel;
public class NewJFrame extends javax.swing.JFrame {
    public NewJFrame() {
        initComponents();
    }
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {
        jComboBox1 = new javax.swing.JComboBox();
        jButton1 = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();
        jTree1 = new javax.swing.JTree();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        jComboBox1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jComboBox1ActionPerformed(evt);
            }
        });
        jButton1.setText("Refresh");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });
        jTree1.setModel(new FileTreeModel());
        jScrollPane1.setViewportView(jTree1);
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(jComboBox1, 0, 173, Short.MAX_VALUE)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 87, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addComponent(jScrollPane1))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jButton1))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 189, Short.MAX_VALUE)
                .addContainerGap())
        );
        pack();
    }// </editor-fold>
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        DefaultComboBoxModel model = new DefaultComboBoxModel(getAvailableRoots());
        jComboBox1.setModel(model);
    }
    private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {
        File choosenRoot = (File) jComboBox1.getSelectedItem();
        if (choosenRoot != null) {
            FileTreeModel model = new FileTreeModel(choosenRoot, false, true);
            jTree1.setModel(model);
        }
    }
    public static void main(String args[]) {
        try {
//            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
//                if ("Nimbus".equals(info.getName())) {
//                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
//                    break;
//                }
//            }
            javax.swing.UIManager.setLookAndFeel(javax.swing.UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
        /*
         * Create and display the form
         */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }
    private Vector<File> getAvailableRoots() {
        Vector<File> v = new Vector<File>(10, 1);
        File userHome = new File(System.getProperty("user.home"));
        if (userHome.isDirectory()) {
            v.addElement(userHome);
        }
        File[] roots = File.listRoots();
        for (File root : roots) {
            v.addElement(root);
        }
        String os = System.getProperty("os.name").toLowerCase();
        boolean isUnix = (os.indexOf("nix") >= 0 || os.indexOf("nux") >= 0);
        if (isUnix) {
            roots = new File("/media").listFiles();
            for (File root : roots) {
                v.addElement(root);
            }
        }
        return v;
    }
    // Variables declaration - do not modify
    private javax.swing.JButton jButton1;
    private javax.swing.JComboBox jComboBox1;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTree jTree1;
    // End of variables declaration
}

Answer 1

两个问题（我可以解决）是：

1. 你没有缓存你的结果。文件列表是一项昂贵的操作，需要时间。在外部设备上更是如此。一旦你列出了一个目录，就要维护这个列表。如果你使用的是Java 7，你可以使用Fie Watcher服务，否则，你需要提供一个刷新选项
2. 您应该将节点子级的加载卸载到后台任务中。看看http://www.jroller.com/Thierry/entry/swing_lazy_loading_in_a&http://www.jroller.com/Thierry/entry/swing_lazy_loading_in_jtree。虽然不完美，但尝试提供一个好主意

更新

当你看代码时，会发现有很多事情发生。对于单个节点，可能没有什么重要的，但当你开始获得几个节点时，延迟会开始变得明显。

因此，每当树需要重新绘制时，它都会通过调用getChildCount、getChildren和/或getChildAt来遍历每个单独的节点。每一种方法本质上都在做同样的事情，一遍又一遍。

@Override
public int getChildCount(Object parent) {
    if (parent instanceof java.io.File && ((java.io.File) parent).canRead()) {
        List<File> files = children(parent);
        int result = 0;
        for (java.io.File file : files) {
            if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                    && ((!file.isHidden() && !showHidden) || showHidden)) {
                result++;
            }
        }
        return result;
    }
    return 0;
}
@Override
public Object getChild(Object parent, int index) {
    if (parent instanceof java.io.File) {
        List<File> files = children(parent);
        List<java.io.File> resultFiles = new LinkedList<>();
        for (java.io.File file : files) {
            if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                    && ((!file.isHidden() && !showHidden) || showHidden)) {
                resultFiles.add(file);
            }
        }
        return resultFiles.get(index);
    }
    return null;
}

最好有一个子模型，它包含所有文件的列表，然后基于属性（showHidden和onlyFolders）生成一个缓存的子模型，然后可以用来生成每个调用的结果。

例如

@Override
public int getChildCount(Object parent) {
    int count = 0;
    if (parent instanceof java.io.File && ((java.io.File) parent).canRead()) {
        count = fileModel.getFilteredFiles().size();
    }
    return count;
}

这只是一个建议。

此外，根据最近的经验，File.canRead()&File.canWrite()可以在UAC处于活动状态的Windows 7计算机上返回误报：P