android 中 MD5实现

public static String MD5(String plainText)
{		String str = null;
		try
		{
			MessageDigest md = MessageDigest.getInstance("MD5");
			md.update(plainText.getBytes());
			byte b[] = md.digest();

			int i;

			StringBuffer buf = new StringBuffer("");
			for (int offset = 0; offset < b.length; offset++)
			{
				i = b[offset];
				if (i < 0)
					i += 256;
				if (i < 16)
					buf.append("0");
				buf.append(Integer.toHexString(i));
			}
			str = buf.toString().toLowerCase();
		}
		catch (NoSuchAlgorithmException e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return str;
}


下面是一个工具类


package cn.Utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Utils
{

    /**
     * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
     */
    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)
        {
            nsaex.printStackTrace();
        }
    }

    /**
     * 生成字符串的md5校验值
     * 
     * @param s
     * @return
     */
    public static String getMD5(String s)
    {
        return getMD5String(s.getBytes());
    }

    /**
     * 判断字符串的md5校验码是否与一个已知的md5码相匹配
     * 
     * @param password
     *            要校验的字符串
     * @param md5PwdStr
     *            已知的md5校验码
     * @return
     */
    public static boolean checkPassword(String password, String md5PwdStr)
    {
        String s = getMD5(password);
        return s.equals(md5PwdStr);
    }

    /**
     * 生成文件的md5校验值
     * 
     * @param file
     * @return
     * @throws IOException
     */
    public static String getFileMD5String(File file) throws IOException
    {
        InputStream fis;
        fis = new FileInputStream(file);
        byte[] buffer = new byte[1024];
        int numRead = 0;
        while ((numRead = fis.read(buffer)) > 0)
        {
            messagedigest.update(buffer, 0, numRead);
        }
        fis.close();
        return bufferToHex(messagedigest.digest());
    }

    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]; // 取字节中高 4 位的数字转换, >>>
                                                // 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
        char c1 = hexDigits[bt & 0xf]; // 取字节中低 4 位的数字转换
        stringbuffer.append(c0);
        stringbuffer.append(c1);
    }
}