Google Analytics:从刷新令牌获取访问令牌

Question

我正在使用Java中的google analytics api.我有一个代码从刷新令牌中获取访问令牌.我们将刷新令牌存储在数据库中,并在请求时检索访问令牌.

密码更改后,我们的请求令牌变为无效.因此,我通过浏览网址(https://developers.google.com/oauthplayground)并按照说明生成了新的refreshtoken .我得到了新的刷新令牌.现在,当我执行代码来检索访问令牌时,它会抛出空指针异常.以下是代码:

RefreshTokenRequest request = new GoogleRefreshTokenRequest(HTTP_TRANSPORT, JSON_FACTORY, refreshToken,
                    this.clientId, this.clientSecret);
            TokenResponse response = request.execute(); 

调用execute方法时,会抛出以下异常:

java.lang.NullPointerException
    at com.google.api.client.repackaged.com.google.common.base.Preconditions.checkNotNull(Preconditions.java:191)
    at com.google.api.client.util.Preconditions.checkNotNull(Preconditions.java:127)
    at com.google.api.client.json.jackson2.JacksonFactory.createJsonParser(JacksonFactory.java:96)
    at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:85)
    at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:81)
    at com.google.api.client.auth.oauth2.TokenResponseException.from(TokenResponseException.java:88)
    at com.google.api.client.auth.oauth2.TokenRequest.executeUnparsed(TokenRequest.java:287)
    at com.google.api.client.googleapis.auth.oauth2.GoogleRefreshTokenRequest.execute(GoogleRefreshTokenRequest.java:125)
    at com.google.api.client.googleapis.auth.oauth2.GoogleRefreshTokenRequest.execute(GoogleRefreshTokenRequest.java:75)
    at GARTest.main(GARTest.java:22)

任何人都可以指出我做错了什么？我可以从google oAuth UI获取访问令牌.