Learning Java Coding Language: Complete tutorial by Languages Informatic

Author:Languages, Informatic [Languages, Informatic]
Language: eng
Format: epub
Publisher: UNKNOWN
Published: 2020-10-18T16:00:00+00:00

then switch to MBeans tab and find that MBean that we used in our Main class as an ObjectName (in the example above it's ServerManager ). In Attributes section we can see out attributes. If you specified get method only, attribute will be readable but not writeable. If you specified both get and set methods, attribute would be readable and writeable.

Specified methods can be invoked in Operations section.

If you want to be able to use remote management, you will need additional JVM parameters, like:

-Dcom.sun.management.jmxremote=true //true by default

-Dcom.sun.management.jmxremote.port=36006

-Dcom.sun.management.jmxremote.authenticate=false

-Dcom.sun.management.jmxremote.ssl=false

These parameters can be found in Chapter 2 of JMX guides . After that you will be able to connect to your application via jConsole remotely with jconsole host:port or with specifying host:port or

service:jmx:rmi:///jndi/rmi://hostName:portNum/jmxrmi in jConsole GUI.

Useful links:

• JMX guides

• JMX Best practices Read JMX online: https://riptutorial.com/java/topic/9278/jmx

Chapter 98: JNDI

Examples

RMI through JNDI

This example shows how JNDI works in RMI. It has two roles:

• to provide the server with a bind/unbind/rebind API to the RMI Registry

• to provide the client with a lookup/list API to the RMI Registry.

The RMI Registry is part of RMI, not JNDI.

To make this simple, we will use java.rmi.registry.CreateRegistry() to create the RMI Registry.

1. Server.java(the JNDI server)

package com.neohope.jndi.test;

import javax.naming.Context;

import javax.naming.InitialContext;

import javax.naming.NamingException;

import java.io.IOException;

import java.rmi.RemoteException;

import java.rmi.registry.LocateRegistry;

import java.util.Hashtable;

/**

* JNDI Server

* 1.create a registry on port 1234

* 2.bind JNDI

* 3.wait for connection

* 4.clean up and end

*/

public class Server {

private static Registry registry;

private static InitialContext ctx;

public static void initJNDI() {

try {

registry = LocateRegistry.createRegistry(1234);

final Hashtable jndiProperties = new Hashtable();

jndiProperties.put(Context.INITIAL_CONTEXT_FACTORY,

"com.sun.jndi.rmi.registry.RegistryContextFactory");

jndiProperties.put(Context.PROVIDER_URL, "rmi://localhost:1234"); ctx = new InitialContext(jndiProperties);

} catch (NamingException e) {

e.printStackTrace();

} catch (RemoteException e) {

e.printStackTrace();

}

}

public static void bindJNDI(String name, Object obj) throws NamingException { ctx.bind(name, obj); }

public static void unbindJNDI(String name) throws NamingException { ctx.unbind(name);

}

public static void unInitJNDI() throws NamingException { ctx.close();

}

public static void main(String[] args) throws NamingException, IOException { initJNDI();

NMessage msg = new NMessage("Just A Message");

bindJNDI("/neohope/jndi/test01", msg);

System.in.read();

unbindJNDI("/neohope/jndi/test01");

unInitJNDI();

}

}

2. Client.java(the JNDI client)

package com.neohope.jndi.test;

import javax.naming.Context;

import javax.naming.InitialContext; import javax.naming.NamingException; import java.util.Hashtable;

/**

* 1.init context

* 2.lookup registry for the service

* 3.use the service

* 4.end

*/

public class Client {

public static void main(String[] args) throws NamingException { final Hashtable jndiProperties = new Hashtable();

jndiProperties.put(Context.INITIAL_CONTEXT_FACTORY,

"com.sun.jndi.rmi.registry.RegistryContextFactory");

jndiProperties.put(Context.PROVIDER_URL, "rmi://localhost:1234");

InitialContext ctx = new InitialContext(jndiProperties); NMessage msg = (NeoMessage) ctx.lookup("/neohope/jndi/test01"); System.out.println(msg.message);

ctx.close();

}

}

3. NMessage.java (RMI server class)

package com.neohope.jndi.test;

import java.io.Serializable; import java.rmi.Remote;

/** * NMessage

* RMI server class

* must implements Remote and Serializable

*/

public class NMessage implements Remote, Serializable { public String message = "";

public NMessage(String message)

{

this.message = message;

}

}

How to run the eaxmple:

1. build and start the server 2. build and start the client

Introduce

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