java - FileChannel ByteBuffer 和哈希文件

Question

我在 java 中构建了一个文件哈希方法，它采用 filepath+filename 的输入字符串表示形式，然后计算该文件的哈希值。散列可以是任何 native 支持的 ​​java 散列算法，例如 MD2 到 SHA-512。

我正在尝试找出性能的最后一滴，因为这种方法是我正在从事的项目的组成部分。我被建议尝试使用 FileChannel 而不是常规的 FileInputStream。

我原来的方法:

    /**
     * Gets Hash of file.
     * 
     * @param file String path + filename of file to get hash.
     * @param hashAlgo Hash algorithm to use. <br/>
     *     Supported algorithms are: <br/>
     *     MD2, MD5 <br/>
     *     SHA-1 <br/>
     *     SHA-256, SHA-384, SHA-512
     * @return String value of hash. (Variable length dependent on hash algorithm used)
     * @throws IOException If file is invalid.
     * @throws HashTypeException If no supported or valid hash algorithm was found.
     */
    public String getHash(String file, String hashAlgo) throws IOException, HashTypeException {
        StringBuffer hexString = null;
        try {
            MessageDigest md = MessageDigest.getInstance(validateHashType(hashAlgo));
            FileInputStream fis = new FileInputStream(file);

            byte[] dataBytes = new byte[1024];

            int nread = 0;
            while ((nread = fis.read(dataBytes)) != -1) {
                md.update(dataBytes, 0, nread);
            }
            fis.close();
            byte[] mdbytes = md.digest();

            hexString = new StringBuffer();
            for (int i = 0; i < mdbytes.length; i++) {
                hexString.append(Integer.toHexString((0xFF & mdbytes[i])));
            }

            return hexString.toString();

        } catch (NoSuchAlgorithmException | HashTypeException e) {
            throw new HashTypeException("Unsuppored Hash Algorithm.", e);
        }
    }

重构方法:

    /**
     * Gets Hash of file.
     * 
     * @param file String path + filename of file to get hash.
     * @param hashAlgo Hash algorithm to use. <br/>
     *     Supported algorithms are: <br/>
     *     MD2, MD5 <br/>
     *     SHA-1 <br/>
     *     SHA-256, SHA-384, SHA-512
     * @return String value of hash. (Variable length dependent on hash algorithm used)
     * @throws IOException If file is invalid.
     * @throws HashTypeException If no supported or valid hash algorithm was found.
     */
    public String getHash(String fileStr, String hashAlgo) throws IOException, HasherException {

        File file = new File(fileStr);

        MessageDigest md = null;
        FileInputStream fis = null;
        FileChannel fc = null;
        ByteBuffer bbf = null;
        StringBuilder hexString = null;

        try {
            md = MessageDigest.getInstance(hashAlgo);
            fis = new FileInputStream(file);
            fc = fis.getChannel();
            bbf = ByteBuffer.allocate(1024); // allocation in bytes

            int bytes;

            while ((bytes = fc.read(bbf)) != -1) {
                md.update(bbf.array(), 0, bytes);
            }

            fc.close();
            fis.close();

            byte[] mdbytes = md.digest();

            hexString = new StringBuilder();

            for (int i = 0; i < mdbytes.length; i++) {
                hexString.append(Integer.toHexString((0xFF & mdbytes[i])));
            }

            return hexString.toString();

        } catch (NoSuchAlgorithmException e) {
            throw new HasherException("Unsupported Hash Algorithm.", e);
        }
    }

两者都返回正确的散列，但重构方法似乎只适用于小文件。当我传入一个大文件时，它完全阻塞了，我不明白为什么。我是 NIO 的新手，所以请多多指教。

编辑:忘记提及我正在通过它进行 SHA-512 测试。

更新:用我现在的方法更新。

    /**
     * Gets Hash of file.
     * 
     * @param file String path + filename of file to get hash.
     * @param hashAlgo Hash algorithm to use. <br/>
     *     Supported algorithms are: <br/>
     *     MD2, MD5 <br/>
     *     SHA-1 <br/>
     *     SHA-256, SHA-384, SHA-512
     * @return String value of hash. (Variable length dependent on hash algorithm used)
     * @throws IOException If file is invalid.
     * @throws HashTypeException If no supported or valid hash algorithm was found.
     */
    public String getHash(String fileStr, String hashAlgo) throws IOException, HasherException {

        File file = new File(fileStr);

        MessageDigest md = null;
        FileInputStream fis = null;
        FileChannel fc = null;
        ByteBuffer bbf = null;
        StringBuilder hexString = null;

        try {
            md = MessageDigest.getInstance(hashAlgo);
            fis = new FileInputStream(file);
            fc = fis.getChannel();
            bbf = ByteBuffer.allocateDirect(8192); // allocation in bytes - 1024, 2048, 4096, 8192

            int b;

            b = fc.read(bbf);

            while ((b != -1) && (b != 0)) {
                bbf.flip();

                byte[] bytes = new byte[b];
                bbf.get(bytes);

                md.update(bytes, 0, b);

                bbf.clear();
                b = fc.read(bbf);
            }

            fis.close();

            byte[] mdbytes = md.digest();

            hexString = new StringBuilder();

            for (int i = 0; i < mdbytes.length; i++) {
                hexString.append(Integer.toHexString((0xFF & mdbytes[i])));
            }

            return hexString.toString();

        } catch (NoSuchAlgorithmException e) {
            throw new HasherException("Unsupported Hash Algorithm.", e);
        }
    }

因此，我尝试使用我的原始示例和最新更新的示例对一个 2.92GB 文件的 MD5 进行哈希处理。当然，任何基准测试都是相对的，因为存在操作系统和磁盘缓存以及其他正在发生的“魔法”，它们会扭曲对相同文件的重复读取……但这是一些基准测试的镜头。我加载了每个方法，并在重新编译后将其关闭了 5 次。基准测试取自最后一次(第 5 次)运行，因为这将是该算法的“ HitTest 门”运行，以及任何“魔法”(无论如何在我的理论中)。

Here's the benchmarks so far: 

    Original Method - 14.987909 (s) 
    Latest Method - 11.236802 (s)

哈希相同的 2.92GB 文件所需的时间减少了 25.03%。还不错。

Answer 1

3条建议:

1) 每次读取后清除缓冲区

while (fc.read(bbf) != -1) {
    md.update(bbf.array(), 0, bytes);
    bbf.clear();
}

2)不要同时关闭fc和fis，多余，关闭fis即可。 FileInputStream.close API 说:

If this stream has an associated channel then the channel is closed as well.

3) 如果你想使用 FileChannel 提高性能

ByteBuffer.allocateDirect(1024);