Class loading using rmi

Hi
I am developing my application as an applet .I use JMF in my application for media streaming. I need the required classes in javax.media and com.ibm( Really this does n't matter. I want to load some classes not written by me ) from a remote machine as reqiured in order to minimise the size of the applet. I cant define any interface since these are not my classes.Can any body give an idea regarding this
A reply will be gratefully acknowledged
Thank you

The server must have all of the following class files in its class path:
implementation (of course)
interface
stubs
skeletons (if not using RMI version 1.2 stubs)
The client should have only:
implementation (of the client)
interface
The web server should have
stubs
any class files that are used on the server as return arguments for RMI calls that are not in the client.
The classpath of rmiregistry should be empty
The server's codebase should point to the root directory or jar file on the web server where the class files are located.
Look at the web server's log files to see what files the client and rmiregistry are trying to load if you are getting errors.

Similar Messages

Dynamic Class Loading (RMI)

Hi,
i have my rmi server, implementing objects,stubs and skeleton classes deployed in my Tomcat server and they are stored under the tomcat root folder.
In anoather jvm iam trying to load the classes thru the below code.
java -Djava.rmi.server.codebase=http://ssd8/tomcat-3.2.4/install_dir/webapps/ROOT/WEB-INF/rmicode stockMarketClient
ssd8 is the hostname(machine) which contains all my rmi server files.
and stockmarketclient is my rmi client.
Iam getting the java.lang.noclassdeffound error.
what may be the problem???
Should i have the security policy file in the client machine.

Please Do tell me if any of the following worked I'll be greatly obliged
1) Try this
java -Djava.rmi.server.codebase=http://servername/dir1/dir2/ RMIServer
This / thing at the end of the URL is very important
2) This is how I did it just Today
Dynamic Class Loading Using RMI
     Server Side
1) Main Interface
2) Implementing Class
3) Stub & Skel                    (RMI Server & Web Server)
4) All Other Classes used by the Server
     Web Server Side
1) Main Interface
2) Stub & Skel                    (RMI Server & Web Server)
3) All Other Classes (not Main Client Class)
     Client Side
1) Main Interface
2) Main Client Class
3) Stubs
4) Security Manager
     RUNNING
SERVER
     java DataServerImpl
CLIENT
     java DataClient xyz
Note
Make Calls as follows
System.setSecurityManager(new LaxSecurityManager());
DataServer server = (DataServer) Naming.lookup("rmi://localhost:1099/DataServer");
Runnable r = (Runnable)server.getNewClass();
r.run();
DON'T make Calls as follows
System.setSecurityManager(new LaxSecurityManager());
DataServer server = (DataServer) Naming.lookup("rmi://localhost:1099/DataServer");
NewClass obj = server.getNewClass();
obj.run();
if done as above provide the Class NewClass to the Client as well ( whole purpose defeated)
Code
     // SecurityManager
import java.rmi.*;
import java.security.*;
public class LaxSecurityManager extends RMISecurityManager
     // All Checks are routed through this method
     public void checkPermission(Permission p)
          // do nothing
     // Main Interface
import java.rmi.*;
public interface DataServer extends Remote
     public boolean login(String usr_name,char[] pass_wrd) throws RemoteException;
     public Object getNewClass() throws RemoteException;
     // Main Server
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
public class DataServerImpl /*extends UnicastRemoteObject*/ implements DataServer
     static
          try
               LocateRegistry.createRegistry(1099);
          catch(Exception e)
               System.err.println("Static " + e);
     public boolean login(String usr_name,char[] pass_wd) throws RemoteException
          System.out.println("Welcome " + usr_name);
          if( pass_wd == null || pass_wd.length == 0 || pass_wd.length > 10 )
               return false;
          return true;
     public Object getNewClass() throws RemoteException
          System.out.println("Returning New Class");
          return new NewClass();
     public DataServerImpl() throws RemoteException
          try
               System.setProperty("java.rmi.server.codebase","http://localhost:8080/");
               UnicastRemoteObject.exportObject(this);
               Naming.rebind("DataServer",this);
          catch(java.net.MalformedURLException e)
               System.err.println("DataServerImpl " + e);
               return;
          System.out.println("Server Registered");
     public static void main(String[] args) throws Exception
          new DataServerImpl();
     // Class Moving Around the Network
public class NewClass implements java.io.Serializable,Runnable
     int num;
     public void run()
          System.out.println("Start the Server with Number = " + num);
     public NewClass()
          num = (int)(Math.random()*1000);
     public String toString()
          return num + "";
     // Client
import java.rmi.*;
public class DataClient
     public static void main(String[] args) throws Exception
          System.setSecurityManager(new LaxSecurityManager());
          String pass = new String();
          if(args.length == 0)
               System.err.println("usage: java DataClient PassWord");
               System.exit(1);
          else
               pass = args[0];
          DataServer server = (DataServer) Naming.lookup("rmi://localhost:1099/DataServer");
          Runnable r = (Runnable)server.getNewClass();
          r.run();
All the Best

Is Dynamic Class Loading(RMI) Possible in EJB?

In Java RMI,it allows dynamic class loading,that is when the stub and interface class files are modified by the server,the client side can download the updated stub and inteface classes.
As the remote interface of EJB extends Javax.ejb.EJBObject which in turn extends java.rmi.remote.Also the Home interface of EJB extends
javax.ejb.EJBHome which also extends java.rmi.remote.
Therefore I wonder if EJB also supports dynamic class
loading as RMI does.If yes,how to do so?Is it the responsibility of the Application Servers and transparent
to client? If No,then is this a defect in EJB??
Thank you very much in advance!!
John

This would be done by the container and is transparent to the client. Most app servers support "hot deploy" where you can deploy beans while the server is running. This requires dynamic class loading.

Problem loading modified classes from CLASSPATH using system class loader

Hi,
I am facing problem to load the modified classes from CLASSPATH.
I have set my CLASSPATH to a directory whose classes will be modified frequently. After the server(web/app) is started, the system class loader, using which am trying to load the classes from the directory where the CLASSPATH is set, am not able to load the modified files without the server restart.
Do I need to have a custom class loader to fix this.
Please help me.
Thanks,
Sureddy

Do I need to have a custom class loader to fix this.Yes.

Dynamic class loading in J2ME

Hi all,
Couple of questions. Is dynamic class loading using classloaders supported in any, if not all versions of J2ME? I guess I should ask first, what exactly does J2ME cover? I see KVM, but do watches and PDA's, set top boxes, refrigerators and so forth all run the same J2ME JVM? Or are their "less feature full" versions? I was hoping the J2ME spec would be the "lowest common denominator" to program for, but I thought I read somewhere that small devices like watches may even have a "smaller" J2ME JVM or something, less capable. So can I write code for J2ME and it will run on all small devices like cell phones, pda's, and so forth? Or is there another J2ME version, perhaps small than J2ME.
So, from what I have found so far, it appears dynamic class loading is done at startup from a DB (of sorts) as opposed to being able to dynamically find/load classes. If this is so, is there any way to support downloading and reloading new classes like you can with J2SE, such as the hot-swap feature of web servers? Does Class.forName() at least work in that you can "replace" a class with a new version, even if it is not able to have a separate classloader instance? My guess is that J2ME supports only a single classloader space, but I thought I read somewhere that Class.forName() is available. J2ME API shows it I believe, but I could be wrong.
Any help on this topic would be appreciated.
Thanks.

Dynamic class loading is not available in most (if not all) J2ME profiles and configurations. Class.forName() is available (at least in the MID profile), but not to be used for dynamic class loading. It can be used when using device-specific APIs where you can try to load a class containing device specific methods (for example a class that works only on certain Nokia phones, and has methods playSound() and vibrate(), which are not available in MIDP), and if you catch a ClassNotFound exception you can load a class that doesn't use the device specific APIs and contains stubs of the methods, or you can disable certain features in you application that need those features. For an example implementation you can have a look at Nokia's Block Game example (available from their developer site - http://www.forum.nokia.com/main.html).
As for your other more general questions about different JVM's and such, you should read all about the different configurations and profiles available in J2ME (plenty of information using in the J2ME link on this site).

How to improve class-loading performance for missing classes

Hi,
do you have any ideas how we can improve the class-loading performance on a weblogic 12c running on jrockit? We spend about 20-30 ms per request in class-loading due to the way hibernate criteria API works (it tries to load quite a lot of missing classes). The only thing I came up with was to invert the class-loading using the weblogic descriptor for those missing classes (which are actually no real classes but some parts of a generated JPQL) which does improve performance a bit.
Thanks
Dimo

Hi,
do you have any ideas how we can improve the class-loading performance on a weblogic 12c running on jrockit? We spend about 20-30 ms per request in class-loading due to the way hibernate criteria API works (it tries to load quite a lot of missing classes). The only thing I came up with was to invert the class-loading using the weblogic descriptor for those missing classes (which are actually no real classes but some parts of a generated JPQL) which does improve performance a bit.
Thanks
Dimo

RMI Dynamic Class Loading

Hello,
I have a standalone Java Client which is connecting to an RMI based svr component on WLS 6.0sp1. However, before connecting to the RMI Svr, I am trying to boot strap couple of other CLASS files from the App Svr. using the RMIClassLoader. Now here's the problem...
I have placed my classes( one which I want to download and instantiate before I start making conventional calls to RMI Svr remote methods) in the folder WL_HOME/config/examples/rmi/*.class
which is the code_base url I use. However, the error I get when trying to download the classs using RMIClass loader is:
No Security Manager: RMI Class Loader disabled"...
due to which I can not even get connected to my remote object after that. Can somebody please tell me how can I set whatever option it is so that I can get this thing working.
I tried using the "Grant all" security policy too on the client side & server side in vain.
Any help is truly appreciated. Thanks a lot!
cl I am trying to

I'll try having a crack at this, see inline comments
Chirag Shah wrote:
Hello,
I have a standalone Java Client which is connecting to an RMI based svr component on WLS 6.0sp1. However, before connecting to the RMI Svr, I am trying to boot strap couple of other CLASS files from the App Svr. using the RMIClassLoader. Now here's the problem...
I have placed my classes( one which I want to download and instantiate before I start making conventional calls to RMI Svr remote methods) in the folder WL_HOME/config/examples/rmi/*.class
which is the code_base url I use. However, the error I get when trying to download the classs using RMIClass loader is:I'll assume that you're using a proper URL (file://) to instanciate your ClassLoader.
>
No Security Manager: RMI Class Loader disabled"...
Does your client explicitly set a SecurityManager using the following command?
if (System.getSecurityManager() == null) {
System.setSecurityManager(new java.rmi.RMISecurityManager());
Also,I believe that it should only be your client changing its policy file (for the network classload).
>
due to which I can not even get connected to my remote object after that. Can somebody please tell me how can I set whatever option it is so that I can get this thing working.
I tried using the "Grant all" security policy too on the client side & server side in vain.
Any help is truly appreciated. Thanks a lot!
cl I am trying toHope it helps,
Stephane Vaucher
CIRANO
Research Professional

No security manager: RMI class loader disabled

i tried to add a filter to my client jmx
my filter is:
class Filter implements NotificationFilter {
public boolean isNotificationEnabled(Notification n) {
          return (n.getType().equals("example.user.remove"))
          ? true
          : false;
in my client i use:
Filter filter=new Filter();
Listener listener=new Listener();
mbeanServer.addNotificationListener(mbeanName, listener, filter, null);
if i dont put the filter(if i use null) my client works but when i include the filter I have this error:
java.rmi.UnmarshalException: java.lang.ClassNotFoundException: Filter (no security manager: RMI class loader disabled); nested exception is:
     java.lang.ClassNotFoundException: Filter (no security manager: RMI class loader disabled)
what is wrong?

You need to make sure that Filter.class is on your classpath, either directly as the .class file or in a JAR file that is on the classpath.

RMI Class Loader

Hi, i Have an application which uses RMI and I need to change at runtime the codebase property to point to a local directory which is not on the CLASSPATH environment variable, so the JVM default Class Loader cannot load the classes located at that local directory. I guess I have to define my own subclass of the class java.rmi.server.RMIClassLoaderSpi and in my code I should change the property "java.rmi.server.RMIClassLoaderSpi" with the method System.setProperty() to point to another RMIClassLoaderSpi subclass as needed, right?
I found the documentation of the class RMIClassLoaderSpi too vague. Can anyone tell me what code to place on which of her methods? An example would be great.

I would suggest another simple approach - launch a new VM for every user application.
I looked at the RMI implementation (you can also download the J2SDK source code and see how internal sun.* classes are implemented) and it looks like you will get the correct codebase annotation if you load your user classes with a URLClassLoader.
Now if you want to use a dynamic codebase property you can have your own RMIClassLoaderSpi. It has a method "getClassAnnotation" which you can implement to return any codebase you wish for your classes.
Genady

Simple RMI/IIOP app : "no security manager: RMI class loader disabled"

Hello colleagues!
I do not understand the problem at all, and asking for your kind help.
This is my first code for RMI/IIOP. We are using JBoss as application server.
What I've done :
1) created test.Command interface , extending Remote
2) created test.CommandImpl , implementing above mentioned interface and java.io.Serializable, and extending javax.rmi.PortableRemoteObject.
BTW, Serializable is not implemented in some tutorials, but absence of Serializable causes NotSerializableException when trying to rebind (next step).
3) in server code, created initial context and called
context.rebind("test/Command",new CommandImpl());
4) Ran rmic -iiop test.CommandImpl . A result was two new cass files, CommandImplTie.class and CommandStub.class , both are also in package "test".
5) Created remote client and put CommandStub.class to client
classpath (under package "test", too).
6) In client code, initialized the context and called
context.lookup("test/Command").
On this line (lookup), the following exception is being raised :
javax.naming.CommunicationException. Root exception is java.lang.ClassNotFoundException: test.CommandImpl (no security manager: RMI class loader disabled)
     at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:368)
     at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:161)
     at java.rmi.server.RMIClassLoader$2.loadClass(RMIClassLoader.java:631)
     at java.rmi.server.RMIClassLoader.loadClass(RMIClassLoader.java:257)
     at sun.rmi.server.MarshalInputStream.resolveClass(MarshalInputStream.java:200)
     at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1513)
     at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1435)
     at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1626)
     at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
     at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
     at java.rmi.MarshalledObject.get(MarshalledObject.java:135)
     at org.jnp.interfaces.MarshalledValuePair.get(MarshalledValuePair.java:30)
     at org.jnp.interfaces.NamingContext.lookup(NamingContext.java:514)
     at org.jnp.interfaces.NamingContext.lookup(NamingContext.java:471)
     at javax.naming.InitialContext.lookup(InitialContext.java:347)
Is _Stub class all that client needs from server classes, to obtain
the reference ? I tried to put _Tie also to client, but with the same result.
All Jndi paths to JBoss server are correct, as I've used them successfully in other applications.
Many thanks in advance,
Daniel

Next few words to the topic.
I made tests with canonical RMI/IIOP tutorial from Sun.
When I use Sun's ORB (orbd.exe) , everything work fine. I started
orbd on the same PC as JBoss, and client and server are running
remotely.
But with JBoss ORB, I have the same exception as described above.
Server starts and registers in JNDI successfully, but client can not
obtain a remote reference. Exception is being thrown on
context.lookup().
So the difference is definitely in security managers for two ORBs.
I also tried to create new RMISecurityMananger and set it, but with
no effect.
Any ideas ?
TIA,
Daniel.

Access to class loader RMI

Hello,
I am writing an RMI-chat program, but I have some problems using dynamic class loading.
I do set my security manager, I've got a java.policy, use the right commandline-options, but I get the following error when I try to dynamicly load a class. The class is on the right server, and the server is running, and properly set in the codebase:
ClassNotFoundException: access to class loader denied.
Can anyone please help me?
Johanna

Sorry,
I was using two codebases, and one was not accesible in the policy file.
My bad

RMI and the class loader delegation model

Hello,
I need to know what the class loader delagation chain looks like when RMI does dynamic class loading. What is the RMIClassLoader's parent? Does it delegate to Thread.currentThread().getContextClassLoader()?
In a test application I can debug the chain which looks like this:
sun.misc.Launcher$AppClassLoader@bac748
sun.misc.Launcher$ExtClassLoader@7172ea
The AppClassLoader is the class loader for the test and is coincident with getSystemClassLoader(). Its parent is the ExtClassLoader which I believe is in charge of loading anything from jre/lib/ext. But I don't know how to get a reference to the RMIClassLoader in order to find out what it's parent is.
I would appreciate any info on this.
Thanks in advance,
Joe

Well that was easy.
I just used the RMIClassLoader.getClassLoader(String codebase) and was able to determine the chain.
FYI: the chian is as follows:
ExtClassLoader <-- AppClassLoader <-- sun.rmi.server.LoaderHandler
Of interest, if you have a custom class loader its parent will most likely be the AppClassLoader but the rmi class loader will not chain off of your custom class loader. It does some interesting things in order for this to work. It will look for custom class loader to load interfaces but will use the RMIClassLoader to load stubs. Pretty cool.
Thanks anyway.
Joe

How can I make server use single class loader for several applications

I have several web/ejb applications. These applications use some common libraries and should share instances of classes from those libraries.
But applications are being deployed independently thus packaging all them to EAR is not acceptable.
I suppose the problem is that each application uses separate class loader.
How can I make AS use single class loader for a set of applications?
Different applications depend on different libraries so I need a way that will not share library for all applications on the domain but only for some exact applications.
When I placed common jar to *%domain%/lib* - all works. But that jar is shared between all applications on the domain.
When I tried to place common jar to *%domain%/lib/applibs* and specified --libraries* attribute on deploying I got exception
java.lang.ClassCastException: a.FirstDao cannot be cast to a.FirstDaoHere http://download.oracle.com/docs/cd/E19879-01/820-4336/6nfqd2b1t/index.html I read:
If multiple applications or modules refer to the same libraries, classes in those libraries are automatically shared.
This can reduce the memory footprint and allow sharing of static information.Does it mean that classes should be able to be casted ?

You didn't specify which version of the application server you are using, but the config is similar as long as you know what to look for. Basically, you need to change the classloader delegation. Here's how it is done in 8.2
http://download.oracle.com/docs/cd/E19830-01/819-4721/beagb/index.html

Dynamic class loading problem using unknown JAR archive and directory names

I read the following article, which enlightened me a lot:
Ted Neward: Understanding Class.forName().
However, it took me some while to understand that my problem is the other way around:
I know the name of the class, I know the name of the method,
but my program/JVM does not know where to load the classes from.
Shortly, my problem is that the server engine that I am writing
uses two different versions of the same library.
So I am trying out the following solution:
My program is named TestClassPathMain.java
Assume the two libraries are named JAR1.jar and JAR2.jar
and the class/instance method that should
be exposed to TestClassPathMain.java by them is named
TestClass1.testMethod().
As long as I was depending on just one library,
I put JAR1.jar in the classpath before starting java,
and I was happy for a while.
At the moment I got the need to use another version of
TestClass1.testMethod() packaged in JAR2.jar,
a call would always access JAR1.jar's
TestClass1.testMethod().
I then decided to remove JAR1.jar from the classpath,
and programmatically define two separate ClassLoaders, one for use
with JAR1.jar and the other for use with JAR2.jar.
However, the problem is only partly solved.
Please refer to the enclosed code for details.
(The code in the JAR1.jar/JAR2.jar is extremely simple,
it just tells (by hardcoding) the name of the jar it is packaged in
and instantiates another class packaged in the same jar using
the "new" operator and calls a method on it. I don't enclose it.)
The TestClassPathMain.java/UC1.java/UC2.java code suite was
successfully compiled with an arbitrary of JAR1 or JAR2 in the classpath,
however removed from the classpath at runtime.
(I know that this could have been done (more elegantly...?) by producing an Interface,
but I think the main problem principle is still untouched by this potential lack of elegancy(?))
1) This problem should not be unknown to you experts out there,
how is it generally and/or most elegantly solved?
The "*** UC2: Variant 2" is the solution I would like best, had it only worked.
2) And why arent "*** UC2: Variant 2" and
"*** static UC2: Variant 2" working,
while "*** Main: Variant 2" is?
3) And a mal-apropos:
Why can't I catch the NoClassDefFoundError?
The output:
*** Main: Variant 1 JAR 1 ***:
Entering TestClass1.testMethod() packaged in JAR1.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR1.jar
*** Main: Variant 1 JAR 2 ***:
Entering TestClass1.testMethod() packaged in JAR2.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR2.jar
*** Main: Variant 2 JAR 1 ***:
Entering TestClass1.testMethod() packaged in JAR1.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR1.jar
*** Main: Variant 2 JAR 2 ***:
Entering TestClass1.testMethod() packaged in JAR2.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR2.jar
*** UC1: Variant 1 JAR 1 ***:
Entering TestClass1.testMethod() packaged in JAR1.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR1.jar
*** UC1: Variant 1 JAR 2 ***:
Entering TestClass1.testMethod() packaged in JAR2.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR2.jar
*** static UC2: Variant 2 JAR 1 ***:
Exception in thread "main" java.lang.NoClassDefFoundError: TestClass1
        at UC2.runFromJarVariant2_static(UC2.java:56)
        at TestClassPathMain.main(TestClassPathMain.java:52)
TestClassPathMain.java
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class TestClassPathMain {
    public static void main(final String args[]) throws MalformedURLException, ClassNotFoundException, InstantiationException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {
            // Commented out because I cannot catch the NoClassDefFoundError.
            // Why?
            try {
                final TestClass1 testClass1 = new TestClass1();
                System.out.println(
                    "\nThe class TestClass1 is of some unexplicable reason available." +
                    "\nFor the purpose of the test, it shouldn't have been!" +
                    "\nExiting");
                System.exit(1);
            } catch (NoClassDefFoundError e) {
                System.out.println("\nPositively confirmed that the class TestClass1 is not available:\n" + e);
                System.out.println("\n\nREADY FOR THE TEST: ...");
            // Works fine
            System.out.println("\n*** Main: Variant 1 JAR 1 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** Main: Variant 1 JAR 2 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Works fine
            System.out.println("\n*** Main: Variant 2 JAR 1 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** Main: Variant 2 JAR 2 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Works fine
            final UC1 uc1 = new UC1();
            System.out.println("\n*** UC1: Variant 1 JAR 1 ***:");
            uc1.runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** UC1: Variant 1 JAR 2 ***:");
            uc1.runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Crashes
            System.out.println("\n*** static UC2: Variant 2 JAR 1 ***:");
            UC2.runFromJarVariant2_static("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** static UC2: Variant 2 JAR 2 ***:");
            UC2.runFromJarVariant2_static("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Crashes
            final UC2 uc2 = new UC2();
            System.out.println("\n*** UC2: Variant 2 JAR 1 ***:");
            uc2.runFromJarVariant2("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** UC2: Variant 2 JAR 2 ***:");
            uc2.runFromJarVariant2("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
    private static void runFromJarVariant1(final String jarFileURL)
        throws MalformedURLException,
               ClassNotFoundException,
               InstantiationException,
               IllegalArgumentException,
               IllegalAccessException,
               InvocationTargetException,
               SecurityException,
               NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final Object testClass1 = clazz.newInstance();
        final Method testMethod1 = clazz.getMethod("testMethod", null);
        testMethod1.invoke(testClass1, null);
    private static void runFromJarVariant2(final String jarFileURL)
        throws MalformedURLException,
               ClassNotFoundException,
               InstantiationException,
               IllegalArgumentException,
               IllegalAccessException,
               InvocationTargetException,
               SecurityException,
               NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final TestClass1 testClass1 = new TestClass1();
        testClass1.testMethod();
UC1.java
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class UC1 {
    public void runFromJarVariant1(final String jarFileURL)
        throws MalformedURLException,
               ClassNotFoundException,
               InstantiationException,
               IllegalArgumentException,
               IllegalAccessException,
               InvocationTargetException,
               SecurityException,
               NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final Object testClass1 = clazz.newInstance();
        final Method testMethod1 = clazz.getMethod("testMethod", null);
        testMethod1.invoke(testClass1, null);
UC2.java
import java.lang.reflect.InvocationTargetException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class UC2 {
    public void runFromJarVariant2(final String jarFileURL)
    throws MalformedURLException,
           ClassNotFoundException,
           InstantiationException,
           IllegalArgumentException,
           IllegalAccessException,
           InvocationTargetException,
           SecurityException,
           NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final TestClass1 testClass1 = new TestClass1();
        testClass1.testMethod();
     * Identic to the "runFromJarVariant2" method,
     * except that it is static
    public static void runFromJarVariant2_static(final String jarFileURL)
    throws MalformedURLException,
           ClassNotFoundException,
           InstantiationException,
           IllegalArgumentException,
           IllegalAccessException,
           InvocationTargetException,
           SecurityException,
           NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final TestClass1 testClass1 = new TestClass1();
        testClass1.testMethod();
}

2. i need to load the class to the same JVM (i.e. to
the same environment) of the current running
aplication, so that when the loaded class is run, it
would be able to invoke methods on it!!!
ClassLoader(s) do this. Try the URLClassLoader.
(I was talking about relatively esoteric "security"
issues when I mentioned the stuff about Class objects
"scope".) You might use the URLClassLoader kind of
like this.
Pseudo-code follows:
// setup the class loader
URL[] urls = new URL[1];
urls[0] = new URL("/path/to/dynamic/classes");
URLClassLoader ucl = new URLClassLoader(urls);
// load a class & use make an object with the default constructor
Object tmp = ucl.loadClass("dynamic.class.name").newInstance();
// Cast the object to a know interface so that you can use it.
// This may be used to further determine which interface to cast
// the class to. Or it may simply be the interface to which all
// dynamic classes have to conform in your program.
InterfaceImplementedByDynamicClass loadedObj =
    (InterfaceImplementedByDynamicClass)tmp;It's really not as hard as it sounds, just write a little test of
this and you will see how it works.

How to use RMI Stub class in programming?

Hi all,
I'm new on RMI.
Is there anyone can explain to me how to use RMI Stub class which is generated by invoking rmic command?
For my testing, I can only invoke rmi object nethod via its remote interface. Then what is stub used for when we are coding?
I do appreciate anyone's help.
Thanks very much,
Xianyi.Ye

When the remote object binds itself to the registry, what is actually bound is the stub.
So when the client does a registry lookup, what it gets is the stub. However from the client's point of view it is just some mystery object that implements the remote interface.
So you never have to use it directly, it is all automatic.

Class loading using rmi

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