检查Google帐户个人资料图片是否已更新

Question

我正在编写一个使用用户个人资料图片的Android应用程序。 我想缓存这些图片，并且只有在我上次获得它们之后才更新它们。

我想要实现的框架代码：

public foo() {
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this).addApi(Plus.API)
            .addScope(Plus.SCOPE_PLUS_LOGIN).build();
    mGoogleApiClient.connect();
}

@Override
public void onConnected(Bundle arg0) {
    try {
        Person currentPerson = Plus.PeopleApi.getCurrentPerson(mGoogleApiClient);
        if (currentPerson != null) {
            String personPhotoUrl = currentPerson.getImage().getUrl();
            // ========================================
            // Here I would like to be able to tell if the image pointed by personPhotoUrl have been updated since
            // the last time I've downloaded it, before I need to re-download it.
            // ========================================               
        } else {
            Toast.makeText(getApplicationContext(),
                    "Person information is null", Toast.LENGTH_LONG).show();
        }
    } catch (Exception e) {
        Toast.makeText(getApplicationContext(), "Identification error, please try again later" , Toast.LENGTH_LONG).show();
    }
}

我测试过看，如果在更改个人资料图片时，网址也在变化，并且发现它没有。

有没有办法判断Google +个人资料图片是否已更新？