我现在可以弄清楚我以前的大部分理解问题.

I could now figure out most of my previous understanding problems.

=1= 生成授权网址

String authorizeUrl = new GoogleAuthorizationCodeRequestUrl(googleClientId,callbackUrl,"https://www.googleapis.com/auth/androidpublisher").build()    
// See why: http://***.com/questions/8433990/when-authenticating-with-oauth-and-***-always-get-error-invalid-grant-on
authorizeUrl += "&approval_prompt=force&access_type=offline"

=2= 认证

由于 server-webflow 不适用于 androidpublisher API，因此客户现在必须手动调用 (1) 中生成的 URL.

Since the server-webflow is not working for the androidpublisher API the customer must now call the URL generated in (1) manually.

=3= 回调

谷歌回调应该处理接下来的步骤.回调包含我们必须使用的参数code".

The google callback should process the next steps. The callback contains the parameter "code" which we have to use.

=4= 请求授权令牌

    // Build the HTTP parameter
    Map<String,String> params = [:]
    params.put("grant_type", "authorization_code")
    params.put("code", code.encodeAsURL())
    params.put("client_id", customer.googleClientId.encodeAsURL())
    params.put("client_secret", customer.googleClientSecret.encodeAsURL())
    params.put("redirect_uri", getCallbackUrl().encodeAsURL())

    // Send the POST request
    // This action might throw an exception in case any parameter were wrong, invalid or not specified.
    String result = HttpRequestHandler.sendRequest("https://accounts.google.com/o/oauth2/token", params);
    JSONElement jsonResult = JSON.parse(result)

    // Map result
    OAuth2Result oAuth2Result = new OAuth2Result()
    oAuth2Result.accessToken = jsonResult.getAt("access_token")
    oAuth2Result.refreshToken = jsonResult.getAt("refresh_token")
    oAuth2Result.ttlSeconds = Integer.parseInt(jsonResult.getAt("expires_in").toString())
    oAuth2Result.tokenType = jsonResult.getAt("token_type") 

=5= 请求刷新令牌

    // Build the HTTP parameter
    Map<String,String> params = [:]
    params.put("grant_type", "refresh_token")
    params.put("refresh_token", this.customer.googleRefreshToken.encodeAsURL())
    params.put("client_id", customer.googleClientId.encodeAsURL())
    params.put("client_secret", customer.googleClientSecret.encodeAsURL())

    // Send the POST request
    // This action might throw an exception in case any parameter were wrong, invalid or not specified.
    String result = HttpRequestHandler.sendRequest("https://accounts.google.com/o/oauth2/token", params);
    JSONElement jsonResult = JSON.parse(result)

    // Map result
    OAuth2Result oAuth2Result = new OAuth2Result()
    oAuth2Result.accessToken = jsonResult.getAt("access_token")
    oAuth2Result.refreshToken = jsonResult.getAt("refresh_token")
    oAuth2Result.ttlSeconds = Integer.parseInt(jsonResult.getAt("expires_in").toString())
    oAuth2Result.tokenType = jsonResult.getAt("token_type")