Code出处：http://hellojava.info/?p=119
# vi codecache.java #名称应尽量与public class后面的名称一样。
import java.io.File;
import javax.management.MBeanServerConnection;
import javax.management.ObjectName;
import javax.management.remote.JMXConnector;
import javax.management.remote.JMXConnectorFactory;
import javax.management.remote.JMXServiceURL;
import com.sun.tools.attach.VirtualMachine;
public class codecache {
private static final String CONNECTOR_ADDRESS =
"com.sun.management.jmxremote.localConnectorAddress";
public static void main(String[] args) throws Exception {
if(args.length != 1){
System.err.println("Must enter one arg: pid");
System.exit(0);
}
VirtualMachine vm = VirtualMachine.attach(args[0]);
JMXConnector connector = null;
try {
String connectorAddress = vm.getAgentProperties().getProperty(
CONNECTOR_ADDRESS);
if (connectorAddress == null) {
String agent = vm.getSystemProperties()
.getProperty("java.home")
+ File.separator
+ "lib"
+ File.separator + "management-agent.jar";
vm.loadAgent(agent);
connectorAddress = vm.getAgentProperties().getProperty(
CONNECTOR_ADDRESS);
}
JMXServiceURL url = new JMXServiceURL(connectorAddress);
connector = JMXConnectorFactory.connect(url);
MBeanServerConnection mbeanConn = connector.getMBeanServerConnection();
ObjectName name = new ObjectName(
"java.lang:type=MemoryPool,name=Code Cache");
System.out.println(mbeanConn.getAttribute(name, "Usage"));
}
finally {
if(connector != null)
connector.close();
vm.detach();
}
}
}
# javac -verbose codecache.java
[search path for class files............... /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.75-2.5.4.2.el7_0.x86_64/jre/lib/ext/dnsns.jar.......
codecache.java:9: package com.sun.tools.attach does not exist #如果报此错误,则说明tools.jar包没找到。
import com.sun.tools.attach.VirtualMachine;
# ln -sv /usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0.x86_64/lib/tools.jar /usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0.x86_64/jre/lib/ext/tools.jar
# javac -verbose codecache.java #编译通过。
# java codecache JavaPid #测试是否能正常运行。
# jar -cvf codecache.jar codecache.class #下面步骤用于生成jar文件。
added manifest
adding: codecache.class(in = 2298) (out= 1219)(deflated 46%)
# java -jar codecache.jar
no main manifest attribute, in codecache.jar
# jar -xf codecache.jar
# cp /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.75-2.5.4.2.el7_0.x86_64/jre/lib/ext/tools.jar ./
# vim META-INF/MANIFEST.MF
Manifest-Version: 1.0
Created-By: 1.7.0_75 (Oracle Corporation)
Class-Path: tools.jar
Main-class: codecache #添加此行，并在后面添加一个空行。
# rm -rf codecache.jar
# jar -cvfm codecache.jar META-INF/MANIFEST.MF codecache.class
# java -jar codecache.jar 27696
javax.management.openmbean.CompositeDataSupport(compositeType=javax.management.openmbean.CompositeType(name=java.lang.management.MemoryUsage,items=((itemName=committed,itemType=javax.management.openmbean.SimpleType(name=java.lang.Long)),(itemName=init,itemType=javax.management.openmbean.SimpleType(name=java.lang.Long)),(itemName=max,itemType=javax.management.openmbean.SimpleType(name=java.lang.Long)),(itemName=used,itemType=javax.management.openmbean.SimpleType(name=java.lang.Long)))),contents={committed=22085632, init=2555904, max=67108864, used=20885568})
上面的信息显示Code Cache区域初始化的时候为2555904，最大为67108864，已占用了22085632，使用了20885568。