andriod 多线程所线程同步，多线程通信-Android Handler Thread

android 实现文件多线程下载的实例，只是下载的demo，文件下载还需要进行文件MD5校验、本地同步等操作才是能够保证文件下载的完整。-Android to achieve multi-threaded download instance, just download the demo file download also need to file MD5 validation, local synchronization and other operations is to ensure