http://wenku.baidu.com/link?url=k_Q9wi-l6KdKRbLMEg-pI2R1FBHVV9zyZMMPmGDfM3V5XH9CBPU4nUiFD8h46HqQBMefbWEO-Qg1kw36a2xGcvfqXjS9drmyBKkwc56iuu3这里介绍比较详细