android 计算程序的MD5值

package com.sun.md5;

import java.security.MessageDigest;

import android.app.Activity;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.Signature;
import android.os.Bundle;
import android.util.Log;

public class ApplicationMd5_Activity extends Activity {
    /** Called when the activity is first created. */
	private static final char HEX_DIGITS[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        PackageManager pm  = getPackageManager();
        try {
			PackageInfo info = pm.getPackageInfo("com.nd.assistance", PackageManager.GET_SIGNATURES);
			Log.i("test", String.format("pkg=%s, sig=%s", info.packageName, signatureMD5(info.signatures)));
			//Log.i("test", String.format("pkg=%s, sig=%s", info.packageName, signatureMD5(info.signatures)));
		} catch (NameNotFoundException e) {
			e.printStackTrace();
		}
    }
	private 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 signatureMD5(Signature[] signatures) {
		try {
			MessageDigest digest = MessageDigest.getInstance("MD5");
			if (signatures != null) {
				for (Signature s : signatures)
					digest.update(s.toByteArray());
			}
			return toHexString(digest.digest());
		} catch (Exception e) {
			return "";
		}
	}
	

     
}