Java入門–ファイルのMD5を求める方法

2017年1月28日

Javaコード:
package com.cftpj;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util {
protected static char hexDigits[] = { '0’, '1’, '2’, '3’, '4’, '5’, '6’, '7’, '8’, '9’, 'a’, 'b’, 'c’, 'd’, 'e’, 'f’ };
protected static MessageDigest messagedigest = null;
static {
try {
messagedigest = MessageDigest.getInstance(“MD5");
} catch (NoSuchAlgorithmException nsaex) {
System.err.println(MD5Util.class.getName()
+ “MessageDigestはMD5Utilをサポートしない");
nsaex.printStackTrace();
}
}
public static String getFileMD5String(File file) throws IOException {
FileInputStream in = new FileInputStream(file);
FileChannel ch = in.getChannel();
MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0,
file.length());
messagedigest.update(byteBuffer);
return bufferToHex(messagedigest.digest());
}
public static String getMD5String(String s) {
return getMD5String(s.getBytes());
}

public static String getMD5String(byte[] bytes) {
messagedigest.update(bytes);
return bufferToHex(messagedigest.digest());
}

private static String bufferToHex(byte bytes[]) {
return bufferToHex(bytes, 0, bytes.length);
}

private static String bufferToHex(byte bytes[], int m, int n) {
StringBuffer stringbuffer = new StringBuffer(2 * n);
int k = m + n;
for (int l = m; l < k; l++) {
appendHexPair(bytes[l], stringbuffer);
}
return stringbuffer.toString();
}

private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
char c0 = hexDigits[(bt & 0xf0) >> 4];
char c1 = hexDigits[bt & 0xf];
stringbuffer.append(c0);
stringbuffer.append(c1);
}
public static boolean checkPassword(String password, String md5PwdStr) {
String s = getMD5String(password);
return s.equals(md5PwdStr);
}

public static void main(String[] args) throws IOException {
long begin = System.currentTimeMillis();

File big = new File(“D:/Users/Kit/Desktop/demo11.txt");
String md5 = getFileMD5String(big);
long end = System.currentTimeMillis();
System.out.println(“md5:" + md5 + “,time:" + ((end – begin) / 1000) + “s");
long begin2 = System.currentTimeMillis();
File big2 = new File(“D:/Users/Kit/Desktop/demo12.txt");
String md52 = getFileMD5String(big2);
long end2 = System.currentTimeMillis();
System.out.println(“md5:" + md52 + “,time:" + ((end2 – begin2) / 1000) + “s");
FileInputStream is = new FileInputStream(“");
}
}