專案需要，計算檔案的MD5和SHA1值，找了一些程式碼效率比較低，有的還晦澀難懂，這裡給出測試後通過，速度也相對較快的程式碼。

        /**
	 * Get the md5 value of the filepath specified file
	 * @param filePath The filepath of the file
	 * @return The md5 value
	 */
	public String fileToMD5(String filePath) {
	    InputStream inputStream = null;
	    try {
	        inputStream = new FileInputStream(filePath); // Create an FileInputStream instance according to the filepath
	        byte[] buffer = new byte[1024]; // The buffer to read the file
	        MessageDigest digest = MessageDigest.getInstance("MD5"); // Get a MD5 instance
	        int numRead = 0; // Record how many bytes have been read
	        while (numRead != -1) {
	            numRead = inputStream.read(buffer);
	            if (numRead > 0)
	                digest.update(buffer, 0, numRead); // Update the digest
	        }
	        byte [] md5Bytes = digest.digest(); // Complete the hash computing
	        return convertHashToString(md5Bytes); // Call the function to convert to hex digits
	    } catch (Exception e) {
	        return null;
	    } finally {
	        if (inputStream != null) {
	            try {
	                inputStream.close(); // Close the InputStream
	            } catch (Exception e) { }
	        }
	    }
	}
	
	/**
	 * Get the sha1 value of the filepath specified file
	 * @param filePath The filepath of the file
	 * @return The sha1 value
	 */
	public String fileToSHA1(String filePath) {
	    InputStream inputStream = null;
	    try {
	        inputStream = new FileInputStream(filePath); // Create an FileInputStream instance according to the filepath
	        byte[] buffer = new byte[1024]; // The buffer to read the file
	        MessageDigest digest = MessageDigest.getInstance("SHA-1"); // Get a SHA-1 instance
	        int numRead = 0; // Record how many bytes have been read
	        while (numRead != -1) {
	            numRead = inputStream.read(buffer);
	            if (numRead > 0)
	                digest.update(buffer, 0, numRead); // Update the digest
	        }
	        byte [] sha1Bytes = digest.digest(); // Complete the hash computing
	        return convertHashToString(sha1Bytes); // Call the function to convert to hex digits
	    } catch (Exception e) {
	        return null;
	    } finally {
	        if (inputStream != null) {
	            try {
	                inputStream.close(); // Close the InputStream
	            } catch (Exception e) { }
	        }
	    }
	}

	/**
	 * Convert the hash bytes to hex digits string
	 * @param hashBytes
	 * @return The converted hex digits string
	 */
	private static String convertHashToString(byte[] hashBytes) {
		String returnVal = "";
		for (int i = 0; i < hashBytes.length; i++) {
			returnVal += Integer.toString(( hashBytes[i] & 0xff) + 0x100, 16).substring(1);
		}
		return returnVal.toLowerCase();
	}
 

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