java:File.deleteOnExit()实现分析塈用于多级目录时的讲究

package net.facesdk.cas;
import java.io.File;
import java.io.FileFilter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class CopyUtils{
    /**
     * NIO方式复制文件<br>
     * 目标文件所在的文件夹如果不存在自动创建文件夹
     * @param src 源文件
     * @param dst 目标文件 
     * @throws IOException
     */
    public static void nioCopyFile(File src,File dst) throws IOException {
        if(null==src||null==dst)
            throw new NullPointerException("src or dst is null");
        if(!src.exists()||!src.isFile())
            throw new IllegalArgumentException(String.format("INVALID FIILE NAME(无效文件名) src=%s",src.getCanonicalPath()));
        if (dst.exists() &&!dst.isFile()) {
            throw new IllegalArgumentException(String.format("INVALID FIILE NAME(无效文件名) dst=%s",dst.getCanonicalPath()));
        }
        File folder = dst.getParentFile();
        if (!folder.exists())
            folder.mkdirs();
        if(((src.length()+(1<<10)-1)>>10)>(folder.getFreeSpace()>>10))
            throw new IOException(String.format("DISK ALMOST FULL(磁盘空间不足) %s",folder.getCanonicalPath()));
        System.out.printf("src=%s,to=%s\n", src.getAbsolutePath(),dst.getAbsolutePath());
        FileInputStream fin=new FileInputStream(src); 
        FileOutputStream fout = new FileOutputStream(dst);
        FileChannel fic = fin.getChannel();
        FileChannel foc = fout.getChannel();
        try {
            ByteBuffer bb = ByteBuffer.allocate((int) fic.size());
            fic.read(bb);
            foc.write(bb);
        } finally {
            fic.close();
            foc.close();
            fin.close();
            fout.close();
        }
    }
    /**
     * 递归复制文件/文件夹到指定的文件夹，并且在JVM结束时删除
     * @param src 原文件/文件夹
     * @param dstFolder 目标文件夹
     */
    public static final void copyAndDeleteOnExit(final File src,final File dstFolder) {
        if(src.isDirectory()){
            src.listFiles(new FileFilter(){
                @Override
                public boolean accept(File pathname) {
                    System.out.printf("pathname=%s\n", pathname.getName());
                    File df = new File(dstFolder,src.getName());                    
                    copyAndDeleteOnExit(pathname,df);                   
                    df.deleteOnExit();// JVM结束时删除指定文件夹在
                    return false;
                }});
        }else{
            try {
                File dst=new File(dstFolder,src.getName());
                nioCopyFile(src,dst);
                // JVM结束时删除文件
                dst.deleteOnExit();
            } catch (IOException e) {           
                e.printStackTrace();
            }
        }
    }
}

    public void deleteOnExit() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
        security.checkDelete(path);
    }
    DeleteOnExitHook.add(path);//将文件路径向DeleteOnExitHook类注册
    }

/*
 * %W% %E%
 *
 * Copyright (c) 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package java.io;

import java.util.*;
import java.io.File;

/**
 * This class holds a set of filenames to be deleted on VM exit through a shutdown hook.
 * A set is used both to prevent double-insertion of the same file as well as offer 
 * quick removal.
 */

class DeleteOnExitHook {
    static {
         sun.misc.SharedSecrets.getJavaLangAccess()
             .registerShutdownHook(2 /* Shutdown hook invocation order */,
                 new Runnable() {
                     public void run() {
                        runHooks();
                     }
                 });
    }
    // 保存待删除文件名的哈希表
    private static LinkedHashSet<String> files = new LinkedHashSet<String>();

    private DeleteOnExitHook() {}
    // 将一个文件路径字符串注册(添加)到待删除列表中 files中,
    // 因为 files 是java.util.LinkedHashSet类型的哈希表，没有重复数据，
    // 所以重复添加无效
    static synchronized void add(String file) {
    if(files == null)
        throw new IllegalStateException("Shutdown in progress");

    files.add(file);
    }
    //JVM结束时删除文件调用的方法
    static void runHooks() {
    LinkedHashSet<String> theFiles;

    synchronized (DeleteOnExitHook.class) {
        theFiles = files;
        files = null;
    }

    ArrayList<String> toBeDeleted = new ArrayList<String>(theFiles);

    // reverse the list to maintain previous jdk deletion order.
    // Last in first deleted.
    Collections.reverse(toBeDeleted);//在这里将待删除文件列表反序了
    for (String filename : toBeDeleted) {
        (new File(filename)).delete();// 顺序删除文件
    }
    }
}

                public boolean accept(File pathname) {
                    System.out.printf("pathname=%s\n", pathname.getName());
                    File df = new File(dstFolder,src.getName());                    
                    copyAndDeleteOnExit(pathname,df);                   
                    df.deleteOnExit();// JVM结束时删除指定文件夹
                    return false;
                }});

                public boolean accept(File pathname) {
                    System.out.printf("pathname=%s\n", pathname.getName());
                    File df = new File(dstFolder,src.getName());                    
                    df.deleteOnExit();// JVM结束时删除指定文件夹
                    copyAndDeleteOnExit(pathname,df);                       
                    return false;
                }});