这个函数给出了与你从mysql的md5函数或php的md5函数等中得到的相同的md5。这是我用的(你可以根据你的需要来改变)

public static String md5( String input ) {
    try {
        java.security.MessageDigest md = java.security.MessageDigest.getInstance("MD5");
        byte[] array = md.digest(input.getBytes( "UTF-8" ));
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < array.length; i++) {
            sb.append( String.format( "%02x", array[i]));
        }
        return sb.toString();
    } catch ( NoSuchAlgorithmException | UnsupportedEncodingException e) {
        return null;            
    }

}

使用java.security.MessageDigest库的简单函数

public String stringMD5Hash(String text) throws NoSuchAlgorithmException {
    MessageDigest messageDigest = MessageDigest.getInstance("MD5");
    byte[] bytes = messageDigest.digest(text.getBytes());
    StringJoiner stringJoiner = new StringJoiner("");
    for (byte b : bytes) {
        stringJoiner.add(Integer.toHexString((b & 0xFF) | 0x100).substring(1, 3));
    }
    return stringJoiner.toString();
}

对于文件使用这个函数

public static String FileMD5Hash(File file) throws NoSuchAlgorithmException, IOException {
    MessageDigest messageDigest = MessageDigest.getInstance("MD5");
    byte[] bytes = messageDigest.digest(getFileBytes(file));
    StringJoiner stringJoiner = new StringJoiner("");
    for (byte b : bytes) {
        stringJoiner.add(Integer.toHexString((b & 0xFF) | 0x100).substring(1, 3));
    }
    return stringJoiner.toString();
}

public static byte[] getFileBytes(File file) throws IOException{
    InputStream inputStream = new FileInputStream(file);
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    byte[] bytes = new byte[1024];
    int bytesRead;
    while ((bytesRead = inputStream.read(bytes)) != -1) {
        byteArrayOutputStream.write(bytes, 0, bytesRead);
    }
    return byteArrayOutputStream.toByteArray();
}

Spring中也有一个DigestUtils类:

http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/util/DigestUtils.html

这个类包含md5DigestAsHex()方法来完成这项工作。

我的回答不是很直白:

private String md5(String s) {
    try {
        MessageDigest m = MessageDigest.getInstance("MD5");
        m.update(s.getBytes(), 0, s.length());
        BigInteger i = new BigInteger(1,m.digest());
        return String.format("%1$032x", i);         
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    }
    return null;
}

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()));

import java.security.MessageDigest

val digest = MessageDigest.getInstance("MD5")

//Quick MD5 of text
val text = "MD5 this text!"
val md5hash1 = digest.digest(text.getBytes).map("%02x".format(_)).mkString

//MD5 of text with updates
digest.update("MD5 ".getBytes())
digest.update("this ".getBytes())
digest.update("text!".getBytes())
val md5hash2 = digest.digest().map(0xFF & _).map("%02x".format(_)).mkString

//Output
println(md5hash1 + " should be the same as " + md5hash2)