java – FileChannel ByteBuffer和Hashing Files
我在
java中构建了一个文件哈希方法,它接受文件路径文件名的输入字符串表示,然后计算该文件的哈希值.散列可以是任何本机支持的java散列算法,例如MD2到SHA-512.
我试图找出最后一滴性能,因为这个方法是我正在研究的项目的一个组成部分.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,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,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,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(),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); } } 两者都返回正确的哈希值,但重构的方法似乎只对小文件合作.当我传入一个大文件时,它完全窒息而我无法弄清楚原因.我是NIO的新手所以请指教. 编辑:忘了提到我正在通过它投掷SHA-512进行测试. 更新:使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,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,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); } } 所以我尝试使用我的原始示例和我最新的更新示例,对2.92GB文件的MD5进行基准测试.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会导致重复读取相同文件的“魔法”……但这里有一些基准测试.我把每个方法加载起来并在将它编译为新鲜后将其关闭5次.基准测试取自最后一次(第5次),因为这将是该算法的“最热门”运行,以及任何“魔术”(在我的理论中无论如何). Here's the benchmarks so far: Original Method - 14.987909 (s) Latest Method - 11.236802 (s) 散布相同的2.92GB文件所花费的时间减少了25.03%.非常好. 解决方法
3意见建议:
1)每次读取后清除缓冲区 while (fc.read(bbf) != -1) { md.update(bbf.array(),bytes); bbf.clear(); } 2)不要关闭fc和fis,这是多余的,关闭fis就足够了. FileInputStream.close API说: If this stream has an associated channel then the channel is closed as well. 3)如果您希望使用FileChannel提高性能 ByteBuffer.allocateDirect(1024); (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |