android对文件的MD5验证

import java.security.MessageDigest;import java.io.FileInputStream;import java.io.InputStream;public class MD5 {    private static final char HEX_DIGITS[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9','A', 'B', 'C', 'D', 'E', 'F' };    public static void main(String[] args)    {        System.out.println(md5sum("/init.rc"));    }    public static String toHexString(byte[] b) {        StringBuilder sb = new StringBuilder(b.length * 2);        for (int i = 0; i < b.length; i++) {            sb.append(HEX_DIGITS[(b[i] & 0xf0) >>> 4]);            sb.append(HEX_DIGITS[b[i] & 0x0f]);        }        return sb.toString();    }    public static String md5sum(String filename) {        InputStream fis;        byte[] buffer = new byte[1024];        int numRead = 0;        MessageDigest md5;        try{            fis = new FileInputStream(filename);            md5 = MessageDigest.getInstance("MD5");            while((numRead=fis.read(buffer)) > 0) {                md5.update(buffer,0,numRead);            }            fis.close();            return toHexString(md5.digest());           } catch (Exception e) {            System.out.println("error");            return null;        }    }}