79 lines
2.2 KiB
Java
79 lines
2.2 KiB
Java
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package com.sequencelogic;
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import java.io.File;
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import java.io.FileInputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import java.security.MessageDigest;
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import java.security.NoSuchAlgorithmException;
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// Digest class for file and message comparison
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public class Digester {
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private static final char[] HexDigits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
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private static final String digestName = "MD5";
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private static MessageDigest digest;
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static {
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try {
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digest = MessageDigest.getInstance (digestName);
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}
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catch (NoSuchAlgorithmException e) {
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throw new RuntimeException ("Could not create an instance of " + digestName);
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}
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}
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public Digester() {
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}
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public static String digest (File file) throws IOException {
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digest.reset();
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return encodeHex (digest.digest (getBytesFromFile (file)));
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}
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public static String digest (String string) {
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digest.reset();
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return encodeHex (digest.digest (string.getBytes()));
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}
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// Encode the digest as a hex encoded string
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public static String encodeHex(byte[] data) {
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int length = data.length;
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char[] out = new char[length << 1];
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for (int i = 0, j = 0; i < length; i++) {
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out[j++] = HexDigits[(0xF0 & data[i]) >>> 4];
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out[j++] = HexDigits[0x0F & data[i]];
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}
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return new String (out);
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}
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private static byte[] getBytesFromFile (File file) throws IOException {
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if (file == null) {
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throw new IllegalArgumentException ("Digester: file cannot be NULL");
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}
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if (!file.exists() && !file.isFile()) {
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throw new IllegalArgumentException("Digester: file must exist and be a file");
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}
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InputStream is = new FileInputStream (file);
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long length = file.length();
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byte[] bytes = new byte[(int) length];
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int offset = 0;
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int numRead = 0;
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while (offset < bytes.length && (numRead = is.read(bytes, offset, bytes.length - offset)) >= 0) {
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offset += numRead;
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}
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if (offset < bytes.length) {
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throw new IOException("Digester: read failed " + file.getName());
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}
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is.close();
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return bytes;
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}
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}
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