Intent intent2 = new Intent();
intent2 = getPackageManager().getLaunchIntentForPackage("com.tmall.wireless"); //這行程式碼比較重要
intent2.setAction("android.intent.action.VIEW");
startActivity(intent2);

 private boolean isAppInstalled(Context context, String uri) {
        PackageManager pm = context.getPackageManager();
        boolean installed = false;
        try {
            pm.getPackageInfo(uri, PackageManager.GET_ACTIVITIES);
            installed = true;
        } catch (PackageManager.NameNotFoundException e) {
            installed = false;
        }
        return installed;
    }