Amazon Turk REST调用java的日期

我想打电话：

https://mechanicalturk.amazonaws.com/?Service=AWSMechanicalTurkRequester
&AWSAccessKeyId=[the Requester's Access Key ID]
&Version=2012-03-25
&Operation=ApproveRejectedAssignment
&Signature=[signature for this request]
&Timestamp=[your system's local time]
&AssignmentId=123RVWYBAZW00EXAMPLE456RVWYBAZW00EXAMPLE

我需要签名，需要UTC时间戳，格式为

YYYY:dd:MMTHH:mm:ss Offset

like

2012-05-25T11:30:47-07:00

我正在尝试使用java工具制作签名，但无法正确格式化日期

我也很喜欢使用SDK，但我不知道从哪里开始

    SimpleDateFormat dateFormatGmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    dateFormatGmt.setTimeZone(TimeZone.getTimeZone("GMT"));

    //Local time zone   
    SimpleDateFormat dateFormatLocal = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    //Time in GMT
    String[] datetime = dateFormatGmt.format(new Date()).split(" ");
    String date = datetime[0];
    String time = datetime[1];

    System.out.print(date+"T"+time+"Z");

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
    Date date = new Date(System.currentTimeMillis());
    System.out.println(sdf.format(date)); // 2012-06-23T00:03:52-0700