JMX监控weblogic的JVM，报java.lang.ClassCastException错误

import java.io.IOException;
import java.net.MalformedURLException;
import java.util.Hashtable;
import javax.management.MBeanServerConnection;
import javax.management.MalformedObjectNameException;
import javax.management.ObjectName;
import javax.management.remote.JMXConnector;
import javax.management.remote.JMXConnectorFactory;
import javax.management.remote.JMXServiceURL;
import javax.naming.Context;

public class PrintJvmState {
   private static MBeanServerConnection connection;
   private static JMXConnector connector;
   private static final ObjectName service;
    // 实例化 RuntimeServiceMBean 对象名
   // 这样可以通过类使用此对象名。
   static {
      try {
         service = new ObjectName( "com.bea:Name=RuntimeService,Type=weblogic.management.mbeanservers.runtime.RuntimeServiceMBean");
      }catch (MalformedObjectNameException e) {
         throw new AssertionError(e.getMessage());
      }
   }
    /*
   * 实例化与 Domain Runtime MBean Server 的连接
   */
   public static void initConnection(String hostname, String portString, 
      String username, String password) throws IOException,
      MalformedURLException { 
      String protocol = "t3";
      Integer portInteger = Integer.valueOf(portString);
      int port = portInteger.intValue();
      String jndiroot = "/jndi/";
      String mserver = "weblogic.management.mbeanservers.runtime";
      JMXServiceURL serviceURL = new JMXServiceURL(protocol, hostname,
         port, jndiroot + mserver);
      Hashtable h = new Hashtable();
      h.put(Context.SECURITY_PRINCIPAL, username);
      h.put(Context.SECURITY_CREDENTIALS, password);
      h.put(JMXConnectorFactory.PROTOCOL_PROVIDER_PACKAGES,
         "weblogic.management.remote");
      connector = JMXConnectorFactory.connect(serviceURL, h);
      connection = connector.getMBeanServerConnection();
   }




   public static ObjectName[] getJVMRuntime() throws Exception {
                   ObjectName serviceRT = (ObjectName) connection.getAttribute(service, "ServerRuntime");
      return (ObjectName[]) connection.getAttribute(serviceRT, "JVMRuntime");
   }
    /* 
   * 迭代 ServerRuntimeMBean，获取名称和状态
   */
   public void printJvmInformation() throws Exception {
                   ObjectName[] jvmRT = getJVMRuntime();
      System.out.println("got jvm runtimes");
      int length = (int) jvmRT.length;
      for (int i = 0; i < length; i++) {
               String name = (String) connection.getAttribute(jvmRT, "Name");
         int HeapSizeCurrent = Integer.parseInt(String.valueOf(connection.getAttribute(jvmRT, "HeapSizeCurrent")));
         int HeapFreeCurrent = Integer.parseInt(String.valueOf(connection.getAttribute(jvmRT, "HeapFreeCurrent")));
         int HeapFreePercent = Integer.parseInt(String.valueOf(connection.getAttribute(jvmRT, "HeapFreePercent")));
         System.out.println("Server name: " + name + ".HeapSizeCurrent: " + HeapSizeCurrent + "HeapFreeCurrent: " + HeapFreeCurrent + "HeapFreePercent: " + HeapFreePercent);
                   }
   }
    public static void main(String[] args) throws Exception {
      String hostname = "*。*。*。*";
      String portString = "7001";
      String username = "weblogic";
      String password = "weblogic";
      PrintJvmState jvm = new PrintJvmState();
      initConnection(hostname, portString, username, password);
      jvm.printJvmInformation();
      connector.close();
   }
}