pendrive 的 JAVA 文件树模型慢

Question

我正在开发一个应用程序，该应用程序将与通过 USB 访问的外部存储器一起工作。 我已经实现了 TreeModel 来浏览磁盘上的目录。它适用于：

• Ubuntu 上的本地磁盘
• 在 Ubuntu 上连接外部存储器
• Windows 7 上的本地磁盘

但在 Windows 7 上连接的外部存储器很糟糕，我不知道为什么。以 pendrive 为根使用此模型滚动 JTree 非常有问题。一开始我认为来自 java.io.File 的 listFiles() 对于 pendrive 来说很慢，所以我在模型中添加了某种缓存，但它没有用 - 滚动仍然很糟糕。

我刚刚注意到它与 Look&Feel 有关。对于 Windows 上的系统 L&F，它很糟糕，对于 Nimbus L&F，它并没有那么糟糕，但仍然不完美。

文件树模型：

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;
    }
}

示例表格：

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（我可以看到）是：

1. 您没有缓存您的结果。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。列出目录后，请维护该列表。如果您使用的是 Java 7，则可以使用 Fie Watcher Service，否则，您将需要提供刷新选项。
2. 您应该将节点子节点的负载卸载到后台任务。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，但请尝试提供一个好主意

更新

当您查看代码时，会发生很多事情。对于单个节点，可能没什么大不了的，但是当您开始获得几个节点时，延迟就会开始变得明显。

因此，每次树需要重新绘制时，它都会在每个单独的节点中爬行调用getChildCount、getChildren 和/或getChildAt。这些方法中的每一种本质上都在一遍又一遍地做同样的事情。

@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;
}

最好有一个包含所有文件列表的子模型，然后根据属性（showHidden 和onlyFolders）生成一个缓存子模型，然后可以使用该子模型生成结果每次通话。

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() 和 File.canWrite() 可能会在 UAC 处于活动状态的 Windows 7 计算机上返回误报：P