磁盘监控。使用java监控磁盘容量，在磁盘容量高于指定大小时自动删除较老的文件以腾出跟多的磁盘空间来存储新的文件-Disk monitoring. Using Java to monitor disk capacity, size specified in the disk capacity is higher than automatically delete the older files to make more disk space to store the new file