JVM常见问题有哪些

cat << \EOF > JmxTest.java

import javax.management.*;
import javax.management.remote.JMXServiceURL;
import javax.management.remote.JMXConnectorFactory;
import javax.management.remote.JMXConnector;
import java.lang.management.RuntimeMXBean;
import static java.lang.management.ManagementFactory.*;
import java.net.Socket;
import java.net.InetSocketAddress;
import java.io.File;
import java.io.IOException;
import java.util.Properties;

// Sun specific
import com.sun.tools.attach.VirtualMachine;

// Sun implementation specific
import sun.management.ConnectorAddressLink;

public class JmxTest {

    /*
     * Starts the management agent in the target VM
     */
    private static void startManagementAgent(String pid) throws IOException {
        /*
         * JAR file normally in ${java.home}/jre/lib but may be in ${java.home}/lib
         * with development/non-images builds
         */
        String home = System.getProperty("java.home");
        String agent = home + File.separator + "jre" + File.separator + "lib"
                + File.separator + "management-agent.jar";
        File f = new File(agent);
        if (!f.exists()) {
            agent = home + File.separator + "lib" + File.separator +
                "management-agent.jar";
            f = new File(agent);
            if (!f.exists()) {
                throw new RuntimeException("management-agent.jar missing");
            }
        }
        agent = f.getCanonicalPath();

        System.out.println("Loading " + agent + " into target VM ...");

        try {
            VirtualMachine.attach(pid).loadAgent(agent);
        } catch (Exception x) {
            throw new IOException(x.getMessage());
        }
    }

    private static void connect(String pid, String address) throws Exception {
        if (address == null) {
            throw new RuntimeException("Local connector address for " +
                                       pid + " is null");
        }

        System.out.println("Connect to process " + pid + " via: " + address);

        JMXServiceURL url = new JMXServiceURL(address);
        JMXConnector c = JMXConnectorFactory.connect(url);
        MBeanServerConnection server = c.getMBeanServerConnection();

        System.out.println("Connected.");

        ObjectName directName = ObjectName.getInstance("java.nio:type=BufferPool,name=direct");
        MBeanInfo mbInfo = server.getMBeanInfo(directName) ;

        for(MBeanAttributeInfo i : mbInfo.getAttributes()) {
            System.out .println(i.getName() + ":" + server.getAttribute(directName , i.getName()));
        }

//        RuntimeMXBean rt = newPlatformMXBeanProxy(server,
//            RUNTIME_MXBEAN_NAME, RuntimeMXBean.class);
//        System.out.println(rt.getName());

        // close the connection
        c.close();
    }


    private final static String LOCAL_CONNECTOR_ADDRESS_PROP =
        "com.sun.management.jmxremote.localConnectorAddress";
		
    public static void main(String[] args) throws Exception {
        String pid =  "1";
        VirtualMachine vm = VirtualMachine.attach(pid);

        String agentPropLocalConnectorAddress = (String)
            vm.getAgentProperties().get(LOCAL_CONNECTOR_ADDRESS_PROP);

        int vmid = Integer.parseInt(pid);
        String jvmstatLocalConnectorAddress =
            ConnectorAddressLink.importFrom(vmid);

        if (agentPropLocalConnectorAddress == null &&
            jvmstatLocalConnectorAddress == null) {
            // No JMX Connector address so attach to VM, and load
            // management-agent.jar
            startManagementAgent(pid);
            agentPropLocalConnectorAddress = (String)
                vm.getAgentProperties().get(LOCAL_CONNECTOR_ADDRESS_PROP);
            jvmstatLocalConnectorAddress =
                ConnectorAddressLink.importFrom(vmid);
        }


        // Test address obtained from agent properties
        System.out.println("Testing the connector address from agent properties");
        connect(pid, agentPropLocalConnectorAddress);

        // Test address obtained from jvmstat buffer
//        System.out.println("Testing the connector address from jvmstat buffer");
//        connect(pid, jvmstatLocalConnectorAddress);


//        // Shutdown application
//        int port = Integer.parseInt(args[1]);
//        System.out.println("Shutdown process via TCP port: " + port);
//        Socket s = new Socket();
//        s.connect(new InetSocketAddress(port));
//        s.close();
    }
}

EOF

javac -Djava.ext.dirs=/usr/java/jdk1.8.0_121/lib JmxTest.java

java -Djava.ext.dirs=/usr/java/jdk1.8.0_121/lib JmxTest