1.   说明
android自带的MD5校验类

2.   例程

1)       功能
对文件/init.rc做MD5计算，并以字串的方式显示

2)       可从此处下载可独立运行的代码
http://download.csdn.net/source/2660824

3)       使用linux命令得到MD5值
$ md5sum init.rc

4)       核心代码及说明
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;
        }
    }
}