不用重新配置，用jconsole连接远程机器进程及获得本地进程的JMX Url的终极办法

估计有很多人都在想用jconsole连接远程机器上的进程时，发现没有配置jmx端口，或者其它的东东。

下面介始一种很简单的办法，可以不用重启远程机器的进程：

ssh -X  192.168.66.66  -l username

连接上去之后，可以直接运行jconsole进程，然后在本机就会弹出一个jconsole的窗口了。

实际上这个不是用jconsole连接远程机器的进程，而是把远程机器上的X输出转地本地来。

如果有提示失败，那么可能要配置下ssh可以转发X。

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但是如果是想用编程的方式去连接本地的Java进程，而又不能更改配置重启。

比如你有个程序是用jmx的方式去得到监控数据的，那么肯定不能重启目标进程，如druid的StatViewServlet：

https://github.com/alibaba/druid/wiki/%E9%85%8D%E7%BD%AE_StatViewServlet%E9%85%8D%E7%BD%AE

可以用下面的方法来得到本地进程的jmx url。

在以前的博客《查找本地进程的jmx url的代码》里有提到ActiveMQ里获得本地进程的jmx url的方法。

http://blog.csdn.net/hengyunabc/article/details/8938281

这个方法有时却不起效，得到的是null，但是用jconsole却又能连接。于是研究了下jconsole的源代码，终于发现，原来jconsole在得不到目标进程的"com.sun.management.jmxremote.localConnectorAddress"环境变量值时，会先尝试让目标进程加载management-agent.jar，这样就可以得到jmx url了。

jconsole的相关源代码OpenJDK源代码下面的 jdk/src/share/classes/sun/tools/jconsole/LocalVirtualMachine.java 里。可以在这里直接看到：

http://hg.openjdk.java.net/jdk7/jdk7/jdk/file/9b8c96f96a0f/src/share/classes/sun/tools/jconsole/LocalVirtualMachine.java

下面是改进后的得到本地进程jmx url的代码，对于异常的处理不是很完善，不过不影响使用：

import java.io.File;
import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.List;
import java.util.Properties;

public class AbstractJmxCommand  {
    private static final String CONNECTOR_ADDRESS =
        "com.sun.management.jmxremote.localConnectorAddress";

    public static String getJVM() {
        return System.getProperty("java.vm.specification.vendor");
    }

    public static boolean isSunJVM() {
        // need to check for Oracle as that is the name for Java7 onwards.
        return getJVM().equals("Sun Microsystems Inc.") || getJVM().startsWith("Oracle");
    }

    public static void main(String[] args) {
		if (args == null || args.length == 0) {
			System.out.println("Usage: pid");
			return;
		}
		int pid = Integer.parseInt(args[0]);
		System.out.println(new AbstractJmxCommand().findJMXUrlByProcessId(pid));
	}
    /**
     * Finds the JMX Url for a VM by its process id
     *
     * @param pid
     * 		The process id value of the VM to search for.
     *
     * @return the JMX Url of the VM with the given pid or null if not found.
     */
    @SuppressWarnings({ "rawtypes", "unchecked" })
    protected String findJMXUrlByProcessId(int pid) {

        if (isSunJVM()) {
            try {
                // Classes are all dynamically loaded, since they are specific to Sun VM
                // if it fails for any reason default jmx url will be used

                // tools.jar are not always included used by default class loader, so we
                // will try to use custom loader that will try to load tools.jar

                String javaHome = System.getProperty("java.home");
                String tools = javaHome + File.separator +
                        ".." + File.separator + "lib" + File.separator + "tools.jar";
                URLClassLoader loader = new URLClassLoader(new URL[]{new File(tools).toURI().toURL()});

                Class virtualMachine = Class.forName("com.sun.tools.attach.VirtualMachine", true, loader);
                Class virtualMachineDescriptor = Class.forName("com.sun.tools.attach.VirtualMachineDescriptor", true, loader);

                Method getVMList = virtualMachine.getMethod("list", (Class[])null);
                Method attachToVM = virtualMachine.getMethod("attach", String.class);
                Method getAgentProperties = virtualMachine.getMethod("getAgentProperties", (Class[])null);
                Method getVMId = virtualMachineDescriptor.getMethod("id",  (Class[])null);

                List allVMs = (List)getVMList.invoke(null, (Object[])null);

                for(Object vmInstance : allVMs) {
                    String id = (String)getVMId.invoke(vmInstance, (Object[])null);
                    if (id.equals(Integer.toString(pid))) {

                        Object vm = attachToVM.invoke(null, id);

                        Properties agentProperties = (Properties)getAgentProperties.invoke(vm, (Object[])null);
                        String connectorAddress = agentProperties.getProperty(CONNECTOR_ADDRESS);

                        if (connectorAddress != null) {
                            return connectorAddress;
                        } else {
                            break;
                        }
                    }
                }

                //上面的尝试都不成功，则尝试让agent加载management-agent.jar
                Method getSystemProperties = virtualMachine.getMethod("getSystemProperties", (Class[])null);
                Method loadAgent = virtualMachine.getMethod("loadAgent", String.class, String.class);
                Method detach = virtualMachine.getMethod("detach", (Class[])null);
                for(Object vmInstance : allVMs) {
                    String id = (String)getVMId.invoke(vmInstance, (Object[])null);
                    if (id.equals(Integer.toString(pid))) {

                        Object vm = attachToVM.invoke(null, id);

                        Properties systemProperties = (Properties)getSystemProperties.invoke(vm, (Object[])null);
                        String home = systemProperties.getProperty("java.home");

                        // Normally in ${java.home}/jre/lib/management-agent.jar but might
                        // be in ${java.home}/lib in build environments.

                        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 IOException("Management agent not found");
                            }
                        }

                        agent = f.getCanonicalPath();

                        loadAgent.invoke(vm, agent, "com.sun.management.jmxremote");

                        Properties agentProperties = (Properties)getAgentProperties.invoke(vm, (Object[])null);
                        String connectorAddress = agentProperties.getProperty(CONNECTOR_ADDRESS);

                        //detach 这个vm
                        detach.invoke(vm, (Object[])null);

                        if (connectorAddress != null) {
                            return connectorAddress;
                        } else {
                            break;
                        }
                    }
                }
            } catch (Exception ignore) {
            	System.err.println(ignore);
            }
        }

        return null;
    }
}