说实话，我有点糊涂了 - 看起来你拥有了一切的这一切 - 这是简单的。但是，让我试着回答你的问题。下面是我的C＃项目中的code，其中我对应用程序的令牌我的意见的情况下，你不熟悉C＃语言和类：

To be honest, I'm a bit confused - looks like you have everything to get it done - and it's simple. But let me try to answer your question. Here is the code from my C# project where I extend app's token with my comments in case you are not familiar with C# languages and classes:

string currentToken = "token from somewhere";

// WebClient is used to send GET request to the given URL
// and receive the response
using (var req = new System.Net.WebClient())
{
    // create URL string and fill it in with data (app Id, secret, and current token)
    var extendTokenUrl = string.Format(
        "https://graph.facebook.com/oauth/access_token?client_id={0}&client_secret={1}&grant_type=fb_exchange_token&fb_exchange_token={2}",
        FB_APP_ID,
        FB_APP_SECRET,
        currentToken);

    // send GET request and download the response
    var response = req.DownloadString(extendTokenUrl);

    // if all is good, response will be a string which looks like this:
    // access_token=<<THE TOKEN GOES HERE>>
    var newToken = response.Substring("access_token=".Length);

    // now save newToken in your DB INSTEAD of currentToken - 
    // so all calls will be made with extended token
    SaveTokenInDB(newToken);
}

希望帮助，并把这种成Java应该是简单的。

hope that helps, and translating this into Java should be straightforward.