private String hashuj(String dane) throws ServletException{
    try {
        MessageDigest m = MessageDigest.getInstance("MD5");
        byte[] bufor = dane.getBytes();
        m.update(bufor,0,bufor.length);
        BigInteger hash = new BigInteger(1,m.dige`enter code here`st());
        return String.format("%1$032X", hash);

    } catch (NoSuchAlgorithmException nsae) {
        throw new ServletException("Algorytm szyfrowania nie jest obsługiwany!");
    }
}

是我做的…似乎还行-我相信有人会指出错误…

public final class MD5 {
public enum SaltOption {
    BEFORE, AFTER, BOTH, NONE;
}
private static final String ALG = "MD5";
//For conversion to 2-char hex
private static final char[] digits = {
    '0' , '1' , '2' , '3' , '4' , '5' ,
    '6' , '7' , '8' , '9' , 'a' , 'b' ,
    'c' , 'd' , 'e' , 'f' , 'g' , 'h' ,
    'i' , 'j' , 'k' , 'l' , 'm' , 'n' ,
    'o' , 'p' , 'q' , 'r' , 's' , 't' ,
    'u' , 'v' , 'w' , 'x' , 'y' , 'z'
};

private SaltOption opt;

/**
 * Added the SaltOption constructor since everybody
 * has their own standards when it comes to salting
 * hashes.
 * 
 * This gives the developer the option...
 * 
 * @param option The salt option to use, BEFORE, AFTER, BOTH or NONE.
 */
public MD5(final SaltOption option) {
    //TODO: Add Char Encoding options too... I was too lazy!
    this.opt = option;
}

/**
 * 
 * Returns the salted MD5 checksum of the text passed in as an argument.
 * 
 * If the salt is an empty byte array - no salt is applied.
 * 
 * @param txt The text to run through the MD5 algorithm.
 * @param salt The salt value in bytes.
 * @return The salted MD5 checksum as a <code>byte[]</code>
 * @throws NoSuchAlgorithmException
 */
private byte[] createChecksum(final String txt, final byte[] salt) throws NoSuchAlgorithmException {
    final MessageDigest complete = MessageDigest.getInstance(ALG);
    if(opt.equals(SaltOption.BEFORE) || opt.equals(SaltOption.BOTH)) {
        complete.update(salt);
    }
    complete.update(txt.getBytes());
    if(opt.equals(SaltOption.AFTER) || opt.equals(SaltOption.BOTH)) {
        complete.update(salt);
    }
    return complete.digest();
}

/**
 * 
 * Returns the salted MD5 checksum of the file passed in as an argument.
 * 
 * If the salt is an empty byte array - no salt is applied.
 * 
 * @param fle The file to run through the MD5 algorithm.
 * @param salt The salt value in bytes.
 * @return The salted MD5 checksum as a <code>byte[]</code>
 * @throws IOException
 * @throws NoSuchAlgorithmException
 */
private byte[] createChecksum(final File fle, final byte[] salt)
        throws IOException, NoSuchAlgorithmException {
    final byte[] buffer = new byte[1024];
    final MessageDigest complete = MessageDigest.getInstance(ALG);
            if(opt.equals(SaltOption.BEFORE) || opt.equals(SaltOption.BOTH)) {
            complete.update(salt);
        }
    int numRead;
    InputStream fis = null;
    try {
        fis = new FileInputStream(fle);
        do {
            numRead = fis.read(buffer);
            if (numRead > 0) {
                complete.update(buffer, 0, numRead);
            }
        } while (numRead != -1);
    } finally {
    if (fis != null) {
            fis.close();
        }
    }
            if(opt.equals(SaltOption.AFTER) || opt.equals(SaltOption.BOTH)) {
            complete.update(salt);
        }
    return complete.digest();
}

/**
 * 
 * Efficiently converts a byte array to its 2 char per byte hex equivalent.
 * 
 * This was adapted from JDK code in the Integer class, I just didn't like
 * having to use substrings once I got the result...
 *
 * @param b The byte array to convert
 * @return The converted String, 2 chars per byte...
 */
private String convertToHex(final byte[] b) {
    int x;
    int charPos;
    int radix;
    int mask;
    final char[] buf = new char[32];
    final char[] tmp = new char[3];
    final StringBuilder md5 = new StringBuilder();
    for (int i = 0; i < b.length; i++) {
        x = (b[i] & 0xFF) | 0x100;
        charPos = 32;
        radix = 1 << 4;
        mask = radix - 1;
        do {
            buf[--charPos] = digits[x & mask];
            x >>>= 4;
        } while (x != 0);
        System.arraycopy(buf, charPos, tmp, 0, (32 - charPos));
        md5.append(Arrays.copyOfRange(tmp, 1, 3));
    }
    return md5.toString();
}

/**
 * 
 * Returns the salted MD5 checksum of the file passed in as an argument.
 * 
 * @param fle The file you want want to run through the MD5 algorithm.
 * @param salt The salt value in bytes
 * @return The salted MD5 checksum as a 2 char per byte HEX <code>String</code>
 * @throws NoSuchAlgorithmException
 * @throws IOException
 */
public String getMD5Checksum(final File fle, final byte[] salt)
        throws NoSuchAlgorithmException, IOException {
    return convertToHex(createChecksum(fle, salt));
}

/**
 * 
 * Returns the MD5 checksum of the file passed in as an argument.
 * 
 * @param fle The file you want want to run through the MD5 algorithm.
 * @return The MD5 checksum as a 2 char per byte HEX <code>String</code>
 * @throws NoSuchAlgorithmException
 * @throws IOException
 */
public String getMD5Checksum(final File fle)
        throws NoSuchAlgorithmException, IOException {
    return convertToHex(createChecksum(fle, new byte[0]));
}

/**
 * 
 * Returns the salted MD5 checksum of the text passed in as an argument.
 * 
 * @param txt The text you want want to run through the MD5 algorithm.
 * @param salt The salt value in bytes.
 * @return The salted MD5 checksum as a 2 char per byte HEX <code>String</code>
 * @throws NoSuchAlgorithmException
 * @throws IOException
 */
public String getMD5Checksum(final String txt, final byte[] salt)
        throws NoSuchAlgorithmException {
    return convertToHex(createChecksum(txt, salt));
}

/**
 * 
 * Returns the MD5 checksum of the text passed in as an argument.
 * 
 * @param txt The text you want want to run through the MD5 algorithm.
 * @return The MD5 checksum as a 2 char per byte HEX <code>String</code>
 * @throws NoSuchAlgorithmException
 * @throws IOException
 */
public String getMD5Checksum(final String txt)
        throws NoSuchAlgorithmException {

    return convertToHex(createChecksum(txt, new byte[0]));
}
}

MessageDigest类可以为您提供MD5摘要的实例。

当使用字符串和加密类时，请确保始终指定您希望字节表示的编码。如果只使用string.getBytes()，它将使用平台默认值。(并非所有平台都使用相同的默认值)

import java.security.*;

..

byte[] bytesOfMessage = yourString.getBytes("UTF-8");

MessageDigest md = MessageDigest.getInstance("MD5");
byte[] theMD5digest = md.digest(bytesOfMessage);

如果你有很多数据，看看.update(xxx)方法，它可以被重复调用。然后调用.digest()来获得结果散列。

如果你真的想要返回一个字符串，而不是字节数组，你总是可以这样做:

String plaintext = "your text here";
MessageDigest m = MessageDigest.getInstance("MD5");
m.reset();
m.update(plaintext.getBytes());
byte[] digest = m.digest();
BigInteger bigInt = new BigInteger(1,digest);
String hashtext = bigInt.toString(16);
// Now we need to zero pad it if you actually want the full 32 chars.
while(hashtext.length() < 32 ){
  hashtext = "0"+hashtext;
}

我发现这是最清晰和简洁的方法:

MessageDigest md5 = MessageDigest.getInstance("MD5");
md5.update(StandardCharsets.UTF_8.encode(string));
return String.format("%032x", new BigInteger(1, md5.digest()));

通过使用java中的MessageDigest类中的方法，可以为给定的文本生成MD5散列。安全包。下面是完整的代码片段，

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import javax.xml.bind.DatatypeConverter;

public class MD5HashGenerator 
{

   public static void main(String args[]) throws NoSuchAlgorithmException
   {
       String stringToHash = "MyJavaCode"; 
       MessageDigest messageDigest = MessageDigest.getInstance("MD5");
       messageDigest.update(stringToHash.getBytes());
       byte[] digiest = messageDigest.digest();
       String hashedOutput = DatatypeConverter.printHexBinary(digiest);
       System.out.println(hashedOutput);
   }
}

MD5函数的输出是由32个十六进制数表示的128位哈希。

如果你使用的是像MySQL这样的数据库，你也可以用一种更简单的方式来做到这一点。查询Select MD5(" text here ")将返回括号中文本的MD5哈希值。