jive 2.5 利用JDK中MessageDigest实现MD5

 

源码:

 

       import java.security.*;
  
       public static MessageDigest digest;
	public synchronized static final String hash(String data) {
        if (digest == null) {  
            try {
                //MD5算法，MD5 16位 SHA 20位
                digest = MessageDigest.getInstance("MD5"); 
                        
              }
            catch (NoSuchAlgorithmException nsae) {
                System.err.println("Failed to load the MD5 MessageDigest. " +
                "Jive will be unable to function normally.");
                nsae.printStackTrace();
            }
        }
        // Now, compute hash. 
        digest.update(data.getBytes()); 
        //填充
        return encodeHex(digest.digest()); 
              
    }

    /**
     * Turns an array of bytes into a String representing each byte as an
     * unsigned hex number.
     * <p>
     * Method by Santeri Paavolainen, Helsinki Finland 1996<br>
     * (c) Santeri Paavolainen, Helsinki Finland 1996<br>
     * Distributed under LGPL.
     *
     * @param bytes an array of bytes to convert to a hex-string
     * @return generated hex string
     */
    public static final String encodeHex(byte[] bytes) {   
        StringBuffer buf = new StringBuffer(bytes.length * 2); 
        int i;

        for (i = 0; i < bytes.length; i++) { 
  //【1】


             if (((int) bytes[i] & 0xff) < 0x10) { 
                //如果bytes[i]补码的低8位小于 16 buf添加0
                buf.append("0");
            }
            //bytes[i] 的低8位，换算成16进制数，添加到buf
            buf.append(Long.toString((int) bytes[i] & 0xff, 16));
        }
        return buf.toString();
    }

    /**
     * Turns a hex encoded string into a byte array. It is specifically meant
     * to "reverse" the toHex(byte[]) method.
     *
     * @param hex a hex encoded String to transform into a byte array.
     * @return a byte array representing the hex String[
     */
    public static final byte[] decodeHex(String hex) {
        char [] chars = hex.toCharArray();
        byte[] bytes = new byte[chars.length/2];
        int byteCount = 0;
        for (int i=0; i<chars.length; i+=2) {
            byte newByte = 0x00;
            newByte |= hexCharToByte(chars[i]); 
            newByte <<= 4;
            newByte |= hexCharToByte(chars[i+1]);
            bytes[byteCount] = newByte;
            byteCount++;
        }
        return bytes;
    }

    /**
     * Returns the the byte value of a hexadecmical char (0-f). It's assumed
     * that the hexidecimal chars are lower case as appropriate.
     *
     * @param ch a hexedicmal character (0-f)
     * @return the byte value of the character (0x00-0x0F)
     */
    private static final byte hexCharToByte(char ch) {
        switch(ch) {
            case '0': return 0x00;
            case '1': return 0x01;
            case '2': return 0x02;
            case '3': return 0x03;
            case '4': return 0x04;
            case '5': return 0x05;
            case '6': return 0x06;
            case '7': return 0x07;
            case '8': return 0x08;
            case '9': return 0x09;
            case 'a': return 0x0A;
            case 'b': return 0x0B;
            case 'c': return 0x0C;
            case 'd': return 0x0D;
            case 'e': return 0x0E;
            case 'f': return 0x0F;
        }
        return 0x00;
    }

 

 

添加测试方法： 看看对字母'h'的散列函数情况

 public static void main(String[] args)
    {
    	System.out.println(MD5.hash("h"));
    }

 同时在【1】处 添加 作为输出分析用

System.out.println("输出bytes["+i+"]"+bytes[i]);

 

结果:

输出bytes[0]-44
输出bytes[1]29
输出bytes[2]-116
输出bytes[3]-39
输出bytes[4]-113
输出bytes[5]0
输出bytes[6]-78
输出bytes[7]4
输出bytes[8]-23
输出bytes[9]-128
输出bytes[10]9
输出bytes[11]-104
输出bytes[12]-20
输出bytes[13]-8
输出bytes[14]66
输出bytes[15]126
d41d8cd98f00b204e9800998ecf8427e

 分析:如： -44补码 低8位 为11010100 =16*13+4=d4 ...

 decodeHex(String hex)就比较容易了