1. Runtime.getRuntime().freeMemory() 和 jvisualvm.exe
http://blog.csdn.net/u011004037/article/details/45740673
2.jmap命令
http://www.cnblogs.com/o-andy-o/archive/2013/06/11/3132335.html
3.mat工具
http://www.open-open.com/lib/view/open1404350384858.html