JVM代码缓存区CodeCache原理及用法解析

package com.javakk;

import java.io.File;
import java.lang.management.ManagementFactory;
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;
/**
 * 基于JMX在运行时查看codeCache使用情况
 * @author 公众号:Java老K
 */
public class CodeCacheTest {
  public static void main(String[] args) throws Exception {
    String pid = getPid(); // 先获取java程序的pid
    String codeCache = getCodeCache(pid); // 根据pid获取codeCache的使用情况
    System.out.println(codeCache);
  }

  /**
   * 获取java进程id
   * @return
   */
  public static String getPid(){
    String name = ManagementFactory.getRuntimeMXBean().getName();
    return name.split("@")[0];
  }

  /**
   * 获取java应用的codeCache使用情况
   * @param pid
   * @throws Exception
   */
  public static String getCodeCache(String pid) throws Exception {
    VirtualMachine vm = VirtualMachine.attach(pid);
    JMXConnector connector = null;
    try {
      String addr = "com.sun.management.jmxremote.localConnectorAddress";
      String property= vm.getAgentProperties().getProperty(addr);
      if (property == null) {
        String agent = vm.getSystemProperties().getProperty("java.home")
            + File.separator
            + "lib"
            + File.separator
            + "management-agent.jar";
        vm.loadAgent(agent);
        property = vm.getAgentProperties().getProperty(addr);
      }

      JMXServiceURL url = new JMXServiceURL(property);
      connector = JMXConnectorFactory.connect(url);
      MBeanServerConnection mbeanConn = connector.getMBeanServerConnection();
      ObjectName obj = new ObjectName("java.lang:type=MemoryPool,name=Code Cache");
      return mbeanConn.getAttribute(obj, "Usage").toString();
    } finally {
      if(connector != null) {
        connector.close();
      }
      vm.detach();
    }
  }
}