Java進程堆外內存（off heap）大小

一、使用ByteBuffer.allocateDirect分配的off heap內存大小

本機進程

• 在Jvisualvm中安裝 Mbeans插件。然后查看java.nio/BufferPool/direct
  

• 進程內使用代碼獲取

MBeanServer mbs = ManagementFactory. getPlatformMBeanServer() ;
ObjectName objectName = new ObjectName("java.nio:type=BufferPool,name=direct" ) ;
MBeanInfo info = mbs.getMBeanInfo(objectName) ;
for(MBeanAttributeInfo i : info.getAttributes()) {
    System.out .println(i.getName() + ":" + mbs.getAttribute(objectName , i.getName()));
}

遠程進程

• JMX獲取
  假設目標機器沒有啟動JMX，那么加入jvm參數：

-Dcom.sun.management.jmxremote.port=9999 
-Dcom.sun.management.jmxremote.authenticate=false 
-Dcom.sun.management.jmxremotAe.ssl=false

重新啟動進程
然后本機通過JMX連接訪問：

String jmxURL = "service:jmx:rmi:///jndi/rmi://10.125.6.204:9999/jmxrmi" ;
JMXServiceURL serviceURL = new JMXServiceURL(jmxURL);
Map map = new HashMap() ;
String[] credentials = new String[] { "monitorRole" , "QED" } ;
map.put( "jmx.remote.credentials" , credentials) ;
JMXConnector connector = JMXConnectorFactory. connect(serviceURL , map);
MBeanServerConnection mbsc = connector.getMBeanServerConnection() ;
ObjectName objectName = new ObjectName("java.nio:type=BufferPool,name=direct" ) ;
MBeanInfo mbInfo = mbsc.getMBeanInfo(objectName) ;
for(MBeanAttributeInfo i : mbInfo.getAttributes()) {
    System.out .println(i.getName() + ":" + mbsc.getAttribute(objectName , i.getName()));
}

二、使用UnSafe反射調用直接申請的堆外內存

java無法獲取。須要相似gperftools之類的工具查看，下次總結