Dynamic Class Instantiating

Hi,
I need to dynamicaly instantiate classes at runtime, that is multiple instances, with different reference variables.
I can easily intantiate a number of classes with different object variables, but i need to do it dynamically at runtime. anyone?

I think u can better solve this by using Hashtable like data-structure.
The key will be a String(external data like phone no.-as u said).
The value will be the actual object which u r trying to load dynamically.
u can load the class dynamically as follows.
Class className=Class.forName("ClassName");
Here class name is the name of the class whose instance u want to create dynamically.If u dont know the
name exactly u need to use reflection.
Object activeObject=className.newInstance();
try this.
-seenu_ch

Similar Messages

Dynamic Class Instantiation with getDefinitionByName

Ok so I am trying to follow the following example in
instantiating a class dynamically:
http://nondocs.blogspot.com/2007/04/flexhowtoinstantiate-class-from-class.html
My AS3 code looks like this:
var myClassName:String = event.templateName;
//Alert.show(getDefinitionByName(myClassName).toString());
try {
var ClassReference:Class = getDefinitionByName(myClassName)
as Class;
var myInstanceObject:* = new ClassReference();
} catch( e:Error ) {
Alert.show("Could not instantiate the class " + myClassName
+ ". Please ensure that the class name is a valid name and that the
Actionscript 3 class or MXML file exists within the project
parameters.");
return;
However I get an error: ReferenceError: Error #1065: Variable
OrderEdit is not defined.
The problem is that my class is located in an altogether
different project directory from the the calling main project (I
include this project with these classes I am trying to dynamically
instantiate in the project source path).
Every example I have seen so far involves some sort of hard
coding. I am builidng a plugin/component that I intend to use in
various places in my site and have any general hard code is
UNACCEPTABLE. How can I make this process COMPLETELY HARD CODE
FREE??
Thanks a ton!

I am also facing the same problem, I have imported swc (flash
created) to flex library path (Flex project >> properties
>> Flex build path >> Library path >> add swc)
These swc files are icons for my applications with some
scripts (written in flash, I am using UIMovieClip). So I want to
make it dynamic.
I write a xml with these component name and want to create a
object and then add that object to my canvas according to xml data.
if I code like this:
var myIcon:IconA = new IconA()
canvas.addChild(myIcon); //canvas is instance of Canvas
then its working, but if I code like
var myDynClass:Class = getDefinitionByName("IconA") as Class
var myIcon:* = new myDynClass()
canvas.addChild(myIcon); //canvas is instance of Canvas
Then its showing me same error
Error
Error #1065: Variable IconA is not defined.
So, I have seen your reply but didn't get it, how can I fix
this problem using modules. or any other way...
Thanks,

Dynamic class instantiation

Win2000
SunOne Studio J2SE
I am developing an application. I would like to instantiate classes and invoke methods dynamically, given a string containing the name of the class and/or a string containing the name of the method.
I have the following code, and it compiles without error. However, when I run it, it throws a "ClassNotFoundException". I have read several articles that explain it as I have coded below.
Any insights are appreciated. Thanks.
try
String className = "TestClass" ;
String methodName = "OutMsg" ;
Class testClass ;
Object testObj ;
Method testMethod ;
testClass = Class.forName(className) ;
testObj = testClass.newInstance() ;
testMethod = testClass.getMethod(methodName, null) ;
testMethod.invoke(testObj, null) ;
catch (InstantiationException exc)
System.out.println(exc) ;
catch (ClassNotFoundException exc)
System.out.println(exc) ;
catch (IllegalAccessException exc)
System.out.println(exc) ;
catch (NoSuchMethodException exc)
System.out.println(exc) ;
catch (InvocationTargetException exc)
System.out.println(exc) ;
public class TestClass
public void OutMsg()
System.out.println("This is a test") ;

You need to put complete class.
I tried
Class.forName("String");
it complains that String is not found.
But if I try
Class.forName("java.lang.String");
it works.
MSN

Help with loading dynamic classes ..need help please

i'm trying to design a program where by i can load dynamic classes
the problem i'm getting is that only one class is loading.
classes are loaded by their names,and index numbers of public methods from a linklist
.When the program runs only the first class is ever loaded and only the methods of that class ..
help please
//class loader
import java.lang.reflect.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.table.*;
public class Test2 extends Thread
     public Class c;
     public Class Ray;
     public Class[] x;
     public static Object object = null;
     public Method[] theMethods;
     public static Method[] method,usemethod;
     public int methodcount;
     public static int MethodCt;
     public static JList list;
public Method[] startClass(String SetMethodName)
     try
          c = Class.forName(SetMethodName);
          object = c.newInstance();
          theMethods = c.getDeclaredMethods();
          // number of methods
          //methodcount = theMethods.length;
     catch (Exception e)
          e.printStackTrace();
// return the array then invoke the particular method later
return theMethods ;
public void RunMethod(Method[] SomeMethod, int methodcount)
     try
          SomeMethod[methodcount].invoke( object,null );
     catch (Exception e)
          e.printStackTrace();
// end class loader
//main calling program
import java.awt.*;
import java.awt.event.*;
import javax.swing .*;
import java.lang.reflect.*;
public class JFMenu extends JFrame
     public static JMenu pluginMenu;
     public static JMenuBar bar;
     public static final Test2 w = new Test2();
public static Method[] setmethod;
private static ClassLinkList startRef = null;
private static ClassLinkList linkRef3 = null;
private static ClassLinkList startRef2 = null;
private String ClassName,ShortCut;
private int MethodNumber;
private JMenuItem PluginItem;
     JFMenu()
          super (" JFluro ");
          JMenu fileMenu = new JMenu("File");
          fileMenu.setMnemonic('F');
          JMenuItem exitItem = new JMenuItem("Exit");
          exitItem.setMnemonic('X');
          fileMenu.add(exitItem);
          exitItem.addActionListener
               new ActionListener()
                    public void actionPerformed(ActionEvent event )
                         System.exit(0);
          JMenu pluginMenu = new JMenu("Plugins");
          pluginMenu.setMnemonic('P');
          startRef = new ClassLinkList ("Hello","Hello ",2,1926,"Painter");
          addToList("Foo","Foo ",0,1930,"Author");
          while (startRef.linkRef5 != null)
               //pluginMenu.addSeparator();
               ClassName = startRef.linkRef5.className;
               ShortCut = startRef.linkRef5.shortcutName;
MethodNumber = startRef.linkRef5.methodNumber;
AddMenuItem(pluginMenu,ShortCut,ClassName,MethodNumber);
               startRef.linkRef5 = startRef.linkRef5.next;
          // create menu bar and add JFMenu window to it
          JMenuBar bar = new JMenuBar();
          setJMenuBar(bar);
          bar.add(fileMenu);
          bar.add(pluginMenu);
          //attributes for JFMenu frame
          setSize(500,200);
          setVisible(true);
     }// end JFMenu constructor
     public void AddMenuItem(JMenu MainMenu, String shortcut,String className, final int methodCount )
          if (MainMenu==null)
               return;
          //JMenuItem item;
          JMenuItem item = new JMenuItem(shortcut);
          MainMenu.add(item);
          setmethod = w.startClass(className);
          item.addActionListener
               new ActionListener()
                    public void actionPerformed(ActionEvent event )
                         w.RunMethod(setmethod,methodCount);
          //item.addActionListener(ij);
     public JMenuItem AddMenuItem2(JMenu MainMenu, String shortcut)
          //if (MainMenu==null)
          //     return Main;
          //JMenuItem item;
          JMenuItem item = new JMenuItem(shortcut);
          MainMenu.add(item);
          //setmethod = w.startClass(className);
          //item.addActionListener(this);
               new ActionListener()
                    public void actionPerformed(ActionEvent event )
                         w.RunMethod(setmethod,methodCount);
          //item.addActionListener(ij);
     return item;
     public void ReloadMenu(JMenuBar Bar, JMenu PluginMenu)
          if (Bar==null)
               return;
          //     setJMenuBar(Bar);
          Bar.add(PluginMenu);
          //item.addActionListener(ij);
public static void main (String args[])
          JFMenu menapp = new JFMenu();
public static void addToList(String clname, String shcutname, int metnumber, int year2,
                              String description) {
     // Create instance of class ClassLinkList
ClassLinkList newRef = new ClassLinkList(clname,shcutname,metnumber,year2,
                                   description);
// Add to linked list;
     startRef = startRef.addRecordToLinkedList(newRef);
// end main calling program
class Hello extends Thread
public int getNum()
System.out.println("I can be ");
return 5;
public void rayshowName()
System.out.println("anything i want ");
public void rayshowName3()
System.out.println("to be ");
class Foo extends Thread
public int getNum()
System.out.println("IMHOFF");
return 5;
public void rayshowName()
System.out.println("raYMOND");
// FAMOUS PERSONS LINKED LIST EXAMPLE
// Frans Coenen
// Saturday 15 January 2000
// Depaertment of Computer Science, University of Liverpool
class ClassLinkList {
/* FIELDS */
public String className;
public String shortcutName;
public int methodNumber;
public int yearOfDeath;
public String occupation;
public ClassLinkList next = null;
public ClassLinkList linkRef5 = this;
public ClassLinkList startRef = null;
/* CONSTRUCTORS */
/* FamousPerson constructor */
public ClassLinkList(String classname, String shortcutname, int methodnumber, int year2,
                              String description) {
     className = classname;
     shortcutName = shortcutname;
     methodNumber = methodnumber;
     yearOfDeath = year2;
     occupation = description;
     next = null;
/* METHODS */
/* Output famous person linked list */
public void outputClassLinkedList()
     //public ClassLinkList outputClassLinkedList() {
     ClassLinkList linkRef = this;
     // Loop through linked list till end outputting each record in turn
while (linkRef != null)
     //System.out.println(linkRef5);
     System.out.println(linkRef.className + ", " + linkRef.shortcutName +
               " (" + linkRef.methodNumber + "-" + linkRef.methodNumber +
               "): " + linkRef.occupation);
     linkRef = linkRef.next;
//return linkRef;
//public String ShowCasname()
//return String ;
/* Add a new record to the linked list */
public ClassLinkList addRecordToLinkedList(ClassLinkList newRef) {
     ClassLinkList tempRef, linkRef;
     // Test if new person is to be added to start of list if so return
if (newRef.testRecord(this) ) {
     newRef.next = this;
     return(newRef);
     // Loop through remainder of linked list
     tempRef = this;
     linkRef = this.next;
     while (linkRef != null) {
     if (newRef.testRecord(linkRef)) {
     tempRef.next = newRef;
          newRef.next = linkRef;
          return(this);
     tempRef = linkRef;
     linkRef = linkRef.next;
// Add to end
tempRef.next = newRef;
     return(this);
/* Delete a record from the linked list given the first and last name. Four
posibilities:
1) Record to be deleted is at front of list
2) Record to be deleted is at end of list
3) Record to be deleted is in middle of list
4) Record not found. */
public ClassLinkList deleteRecord(String lName, String fName) {
ClassLinkList tempRef, linkRef;
// Record at start of list
if ((this.className == lName) & (this.shortcutName == fName))
     return(this.next);
     // Loop through linked list to discover if record is in middle of list.
     tempRef = this;
linkRef = this.next;
while (linkRef != null) {
     if ((linkRef.className == lName) & (linkRef.shortcutName == fName)) {
tempRef.next = linkRef.next;
return(this);
tempRef = linkRef;
linkRef = linkRef.next;
// Record at end of list, or not found
if ((linkRef.className == lName) & (linkRef.shortcutName == fName))
                    linkRef = null;
     else System.out.println("Record: " + lName + " " + fName + " not found!");
     return(this);
/* TEST METHODS */
/* Test whether new record comes before existing record or not. If so return
true, false otherwise. */
private boolean testRecord(ClassLinkList existingRef) {
     int testResult = className.compareTo(existingRef.className);
     if (testResult < 0) return(true);
     else {
     if ((testResult == 0) & (shortcutName.compareTo(existingRef.shortcutName) < 0 ))
                         return(true);
     // Return false
     return(false);
     public void addToList(String clname, String shcutname, int metnumber, int year2,
                              String description)
     // Create instance of class Famous Person
ClassLinkList newRef = new ClassLinkList(clname,shcutname,metnumber,year2,
                                   description);
// Add to linked list;
     startRef = startRef.addRecordToLinkedList(newRef);

I have a similar problem. I am writing a program to read the class names from database and instantiate several classes which extends from ServiceThread (an abstract class extending from Thread).
rs = pStmt.executeQuery();
while(rs.next()) {
String threadclassname = rs.getString("classname").trim();
try{
ServiceThread threadinstance = (ServiceThread)Class.forName(threadclassname).newInstance();
}catch ...
So far, only the first class is ever instantiated and runs fine. But subsequent classes do not even get pass the "... ... Class.forName(...).newInstance();" line.
Funny thing is that there are also no exceptions. The JVM just seem to hang there.

GET SET function in a dynamic Class?

Is it possible to add a GET SET function in a dynamic class, like we can add properties to a dynamic class?

correction :
MyObjectProxy extends ObjectProxy{
override callProperty(
// your dyna logic
and expose new MyObjectProxy(dynaInstance)

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.

Dynamic class loading from directory on server

Hello,
I am not sure if this is right forum, but I think it is more weblogic then ADF issue...
I am trying to create and load dynamically classes in weblogic (10.3.2.0). It is ADF application which I deploy to the weblogic server.
When I print ((GenericClassLoader)this.getClass().getClassLoader()).getFinderClassPath()I see the path to my directory (of course not just this path) C:\...\system11.1.1.2.36.55.36\DefaultDomain\servers\DefaultServer\tmp\_WL_user\test\753the\dynamicClasses(I have added directory dynamicClasses to manifest for deployment WAR profile).
In this directory I create class files. I have checked it, files are really created there.
When I try to load created class with the same classloader, for which I have printed classpath, ClassNotFoundException is thrown.
Please where could be the problem? Isn't it possible to load classes from directory instead of jar, do I need some special server configuration,...?
Thank you in advance
Qjeta

Hi Qjeta,
I am not sure but you can give it a try using URLClassLoader...Which we generally use for DynamicClassLoading:
import java.net.URLClassLoader;
<font color=maroon>
String path="C:/.../system11.1.1.2.36.55.36/DefaultDomain/servers/DefaultServer/tmp/_WL_user/test/753the/dynamicClasses";
*URLClassLoader loader = new URLClassLoader(new URL[] { new URL(path) });*
Class c = loader.loadClass ("your.class.NameHere");
</font>
// Load class from class loader. filly qualified class name (means classname with package name) is the name of the class to be loaded
in the above code the "C:/.../system11.1.1.2.36.55.36/DefaultDomain/servers/DefaultServer/tmp/_WL_user/test/753the/dynamicClasses" should be the location of the directory where your classes are placed....If you want to load a perticular Jar then you need to write the jarfile name as well like following:
C:/.../system11.1.1.2.36.55.36/DefaultDomain/servers/DefaultServer/tmp/_WL_user/test/753the/dynamicClasses/Myapplication.jar
.================================
If the above code works for you then later you can even try to enhance your code by doing the following:
Thread.currentThread().setContextClassLoader(urlClassLoaderRef);
Thanks
Jay SenSharma
http://jaysensharma.wordpress.com (WebLogic Wonders Are Here)

Dynamic Class Loading and Unloading

I am trying to create a system where the class name and method name is
picked up from a meta-data database and executed.
This was accompanied using Dynamic Class loading. I tried to extend this to
support versioning of meta-data. Here depending on the version of meta-data
different libraries can be loaded and different implementations of object
with the same name can be executed. This does not seem to work with Forte
3.0.
When the second Library is loaded the method execution does not work.
(Even though the unload flag on the LoadLibrary is set)
If the application is stopped and restarted pointing to the second library
there is no problem. In a running application a dynamically loaded library
does not seem to unload and reload a new library for the same class names.
Has anyone tried sometime similar, is there a workaround for this type of
problem.
- Vivek

I am trying to create a system where the class name and method name is
picked up from a meta-data database and executed.
This was accompanied using Dynamic Class loading. I tried to extend this to
support versioning of meta-data. Here depending on the version of meta-data
different libraries can be loaded and different implementations of object
with the same name can be executed. This does not seem to work with Forte
3.0.
When the second Library is loaded the method execution does not work.
(Even though the unload flag on the LoadLibrary is set)
If the application is stopped and restarted pointing to the second library
there is no problem. In a running application a dynamically loaded library
does not seem to unload and reload a new library for the same class names.
Has anyone tried sometime similar, is there a workaround for this type of
problem.
- Vivek

Dynamic class reloading in modular web application

Hi.
My web application has these requirements:
A. Functional modularization (like plug-ins). Modules will be simple jars containing application logic classes: dto beans, business logic services, dao (jpa), framework stuff (Struts2), etc...
B. At runtime and without restarting the application "class loading" must be aware of classes inside new, changed and removed modules.
C. Some of these jars will be outside the web application folder (WEB-INF/lib), possibly outside the container itself too.
My question:
1. Can I achieve all or some of my requirements with a Java web application?
2. How should I manage the modules?
3. Do I need some special web container feature (maybe osgi)?
4. Can I use a custom class loader in my application?
The architecture objectives are:
I. Provide scalability.
II. Efficient development process (independent deployment and no application restart required).
III. Better production support (no application restart required for changes).
More on the architecture:
a). Functional scalability, meaning this that my application may functionally grow up to an indeterminate number of small functional modules.
b). Modules will be developed, deployed and maintained independently so the application discovers and loads classes on demand.
c). Avoid a big .war file containing all the small modules because a small change in one module would involves deploying all the other modules (possibly hundreds o even thousands of them) and restarting the application.
d). Above point involves dynamic class reloading.
I guess this is addressed by OSGI (looks like heavy to deal with), Jigsaw (still under development) and maybe others. I think the key point is the class loader. I will develop a custom class loader but maybe you have some advice for me before starting to develop.
Thanks and regards.

Classes maintained by the container should not be loaded by an application. You want the container to read those classes and react accordingly. Most of those classes are read when the container starts up a container restart will be required. Trying to leverage another container within a container does not sound like it will be worth (if you can get it to work).
Perhaps you should state the problem that you are trying to solve with these modules so that others may suggest more feasible solutions to achieve your target goals.

Dynamic class loading failed, why?

Hi there!
We are using WebLogic 5.1 togehter with Apache1.3.22/Tomcat4.01. It all worked
fine for about 2 month. All of a sudden, dynamic class loading refuses to work.
From one day to the other I got the excpetion: javax.naming.CommunicationException.
Root exception is weblogic.rmi.UnmarshalException: Unmarshalling return
- with nested exception:
[java.lang.ClassNotFoundException: class com.dsh.egb.aks.betrieb.ejbs.AnmeldenEJBHomeImpl_ServiceStub
previously not found]
Why does this happen? I can not remember having touched any properties.
Please help,
Heiner

If you were relying on client network classloading stubs from WebLogic, you
can test if it still works by pointing your browser to
htpp://yourweblogic:7001/classes/com/dsh/egb/aks/betrieb/ejbs/AnmeldenEJBHomeImpl_ServiceStub.class
Heiner Amthauer <[email protected]> wrote:
Hi there!
We are using WebLogic 5.1 togehter with Apache1.3.22/Tomcat4.01. It all worked
fine for about 2 month. All of a sudden, dynamic class loading refuses to work.
From one day to the other I got the excpetion: javax.naming.CommunicationException.
Root exception is weblogic.rmi.UnmarshalException: Unmarshalling return
- with nested exception:
[java.lang.ClassNotFoundException: class com.dsh.egb.aks.betrieb.ejbs.AnmeldenEJBHomeImpl_ServiceStub
previously not found]
Why does this happen? I can not remember having touched any properties.
Please help,
Heiner--
Dimitri

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).

Dynamic class loading when CODEBASE is unreachable. A bug?

Let us suppose that we have a large-scale distributed application with ca. 1000 participants communicating via RMI and utilizing dynamic class loading. As we all know, a HTTP code server must be available for this purpose in order to provide dynamically downloaded code, usually the communication proxy code of remote objects. In a real-world scenario, the HTTP server will never be 100% available, so that we will have cases that a Java process will not be able to download the necessary Java classes, causing the RMI communication to fail with a ClassNotFoundException or similar exception. In such a case, a robust application would perform some recovery activities and retry the remote call. Eventually, the HTTP server becomes available again and the distributed system recovers automatically. This seems to work fine with J2SE 1.4.2_10, but not with 1.4.2_11 and newer versions. Considering Java 5, the Update 9 exhibits the same problem.
For tracking down the problem, I've written a simple distributed test application, consisting of a client and a server. A server listens on a port, and sends a MarshalledObject to the client. The code of the MarshalledObject is annotated with the value of the "java.rmi.server.codebase" system property. The annotation contains an URL of the JAR file containing the code of the original object. The client connects to the server, reads data form the socket and unmarshalls the original object. This is basically the same procedure as when objects are accross the wire as arguments/return values/exceptions by the RMI/JRMP engine. This procedure is repeated forever in the loop. Due to the fact that the client's CLASSPATH doesn't contain the code of the original object, this code should dynamically be loaded from the HTTP server using the appropriate annotation provided by the server.
If we start the client while the HTTP server is down, the client will keep generating the ClassNotFoundException over and over again, as expected. So far, so good. If we now start the HTTP server while the client is still running, we will observe different behaviors, depending on the version of the client's JVM:
1. In J2SE 1.4.2_10, the client will download the code from the HTTP server and successfully unmarshal the original object sent by the server. ClassNotFoundExceptions will not be generated again.
2. In J2SE 1.4.2_11, 1.4.2_12 and 1.4.2_13 as well as in J2SE 5.0 Update 9, the client will continue generating ClassNotFoundExceptions. Analysis of the HTTP server's access log shows that there were no attempts to download the JAR file required for unmarshaling the object sent by the server.
It seems that in the newer JVM versions the RMI engine remembers URLs which have failed and does not attempt to access them anymore. Althogh this may have some advantages considering the overall network load, the dynamical class loading becomes practically useless in productive large distributed systems. The very first attempt to load the codebase of the communication peer must succeed, otherwise the whole process must be restarted for the communication to work, which is a very expensive (and for most customers unacceptable) operation in terms of preformance and resources usage.
Should this be seen as a bug or a feature of the JVM? What do you think?
Regards,
Miran
Here is the code to reproduce:
Server code
package server;
import java.net.*;
import java.rmi.*;
import java.io.*;
public class Server implements Serializable {
private int value = 42;
public Server() {
public String toString() {
    return "The Answer is " + value;
public static void main( String[] args ) {
    if( args.length!=1 ) {
      System.out.println( "Usage: server.Server <port>" );
      System.exit( 1 );
    try {
      MarshalledObject data = new MarshalledObject( new Server() );
      int port = Integer.parseInt( args[0] );
      ServerSocket serverSocket = new ServerSocket( port );
      System.out.println( "Accepting connections..." );
      while( true ) {
        Socket s = serverSocket.accept();
        new Thread( new SocketHandler( s, data ) ).start();
    } catch( Exception ex ) {
      ex.printStackTrace();
    System.exit( 0 );
public static class SocketHandler implements Runnable {
    private Socket s;
    private Serializable data;
    public SocketHandler( Socket s, Serializable data ) {
      this.s = s;
      this.data = data;
    public void run() {
      try {
        OutputStream os = s.getOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream( os );
        oos.writeObject( data );
        oos.close();
        os.close();
        s.close();
        System.out.println( "Serving socket succeeded" );
      } catch( Exception ex ) {
        System.out.println( "Serving socket failed" );
        ex.printStackTrace();
Client code
package client;
import java.rmi.*;
import java.net.*;
import java.io.*;
public class Client {
public static void main( String[] args ) {
    if( args.length!=1 ) {
      System.out.println( "Usage: client.Client <port>" );
      System.exit( 1 );
    try {
      if( System.getSecurityManager()==null ) {
        System.setSecurityManager( new RMISecurityManager() );
      int port = Integer.parseInt( args[0] );
      for( int i = 1; true; ++i ) {
        try {
          Socket s = new Socket( "localhost", port );
          InputStream is = s.getInputStream();
          ObjectInputStream ois = new ObjectInputStream( is );
          Object o = ois.readObject();
          ois.close();
          is.close();
          s.close();
          Object umo = ((MarshalledObject) o).get();
          System.out.println( i + ". Retreiving MarshalledObject succeeded: "
                              + umo );
        } catch( Exception ex ) {
          System.out.println( i + ". Retreiving MarshalledObject failed" );
          ex.printStackTrace();
        System.out.println( i + ". Waiting for 10 sec" );
        Thread.sleep( 10000 );
    } catch( Exception ex ) {
      ex.printStackTrace();
    System.exit( 0 );
Start command for the server
java -cp server.jar -Djava.rmi.server.codebase="http://localhost/playground/server.jar" server.Server 33933
Start command for the client
java -cp client.jar -Djava.security.policy=all.policy client.Client 33933
The policy.all file should look as follows
// All permissions
grant {
   permission java.security.AllPermission;
};The server.jar file should only contain the classes from the server package. This file should also be made accessible via HTTP (e.g. by using the Apache HTTP server).
The client.jar file should only contain the classes from the client package.

no body know about this??

Dynamic Class Loading and Stubs

How Dynamic Class Loading is used on Java RMI, since stubs are generated on clients using Reflection API?
I was reading Dynamic code downloading using JavaTM RMI (http://java.sun.com/javase/6/docs/technotes/guides/rmi/codebase.html), it seems to be out of date.
For example, "The client requests the class definition from the codebase. The codebase the client uses is the URL that was annotated to the stub instance when the stub class was loaded by the registry. Back in step 1, the annotated stub for the exported object was then registered with the Java RMI registry bound to a name."

"Enhancements in J2SETM 5.0
Dynamic Generation of Stub Classes
This release adds support for the dynamic generation of stub classes at runtime, obviating the need to use the Java(tm) Remote Method Invocation (Java RMI) stub compiler, rmic, to pregenerate stub classes for remote objects. *Note that rmic must still be used to pregenerate stub classes for remote objects that need to support clients running on _earlier versions_.*
When an application exports a remote object (using the constructors or static exportObject methods(1) of the classes java.rmi.server.UnicastRemoteObject or java.rmi.activation.Activatable) and a pregenerated stub class for the remote object's class cannot be loaded, the remote object's stub will be a java.lang.reflect.Proxy instance (whose class is dynamically generated) with a java.rmi.server.RemoteObjectInvocationHandler as its invocation handler.
An existing application can be deployed to use dynamically generated stub classes unconditionally (that is, whether or not pregenerated stub classes exist) by setting the system property java.rmi.server.ignoreStubClasses to "true". If this property is set to "true", pregenerated stub classes are never used.
Notes:
* If a remote object has pre-5.0 clients, that remote object should use a stub class pregenerated with rmic or the client will get an ClassNotFoundException deserializing the remote object's stub. Pre-5.0 clients will not be able to load an instance of a dynamically generated stub class, because such a class contains an instance of RemoteObjectInvocationHandler, which was not available prior to this release.
* Prior to the J2SE 5.0 release, exporting a remote object would throw a java.rmi.StubNotFoundException if the pregenerated stub class for the remote object's class could not be loaded. With the added support for dynamically generated stub classes, exporting a remote object that has no pregenerated stub class will silently succeed instead. A user deploying a server application to support pre-5.0 clients must still make sure to pregenerate stub classes for the server's remote object classes, even though missing stub classes are no longer reported at export time. Such errors will instead be reported to a pre-5.0 client when it deserializes a dynamically generated stub class.
(1) The static method UnicastRemoteObject.exportObject(Remote) is declared to return java.rmi.server.RemoteStub and therefore cannot be used to export a remote object to use a dynamically generated stub class for its stub. An instance of a dynamically generated stub class is a java.lang.reflect.Proxy instance which is not assignable to RemoteStub."
http://java.sun.com/j2se/1.5.0/docs/guide/rmi/relnotes.html

Dynamic class & property

Hi there!
I would like to know, if it is possible to mimic the behavior of XML dynamic class:
var xm:XML =
    <question idAttr="atribute xml">
    </question>;
trace(xm.attributes());
trace("Attributes: "+xm["attributes"]);
xm["attributes"] = {a:"atr1", b:"atr2"}; (in my dynamic class with attributes function, I get ReferenceError: Error #1037)
trace("Attributes: "+xm["attributes"]);
trace(xm.attributes());
So I can call:
     xm.attributes() method which gives me XML attributes
and use
     xm["attributes"] = {a:"atr1", b:"atr2"};
which writes to the "attributes" property and not references the XML class function.
My question:
How can I do the same in my custom dynamic class ?
Gregory

As you might noticed some syntaxes of XML class' properties and methods are not conventional to AS3. This, perhaps, hints to the fact that XML class is not an AS3 class in its purest sense. In other words it is probably written in a different language (C? C++?...).
In AS3, unlike in other languages, you cannot name property and method the same. So, there is no way to have both "attributes" property and "attributes()" method.
Nevertheless, if you want to emulate XML functionality to some extend and enumerate/return dynamically set properties, you can definitely do that. This is an excellent case for using accessors (setters and getters):
package
     public dynamic class DynamicClass
          public function DynamicClass()
          public function get attributes():Object {
               var obj:Object = { };
               for (var prop:String in this) {
                    obj[prop] = this[prop];
               return obj;
          public function set attributes(obj:Object):void {
               for (var prop:String in obj) {
                    this[prop] = obj[prop];
Usage:
var dc:DynamicClass = new DynamicClass();
dc.prop2 = "BLAH";
dc.attributes = { propA: "bbb", anotherProp: 456 };
trace(dc["attributes"]);
for (var prop:String in dc.attributes) {
     trace(prop, "=", dc.attributes[prop]);
Message was edited by: Andrei1

Dynamic Class

With Dynamic Classes you can add properties at run time. But
the same can be done with Non Dynamic classes using their prototype
property. For e.g. I've a Person Class for which the code is as
follows:
class Person {
private var id:Number;
function Person() {
id = 007;
Now is used this class in a fla file and make two instances
var xx:Person=new Person()
var yy:Person=new Person()
trace(xx.__name) //undefined
trace(yy.__name) //undefined
Person.prototype.__name="myPersonClass"
trace(xx.__name) //myPersonClass
trace(yy.__name) //myPersonClass
If this is true then whats the difference between dynamic and
Non Dynamic classes coz using the prototype property we can convert
every class into dynamic class.

with a dynamic class you could assign distinct __name
properties to each instance.
what you did was to extend the Person class so it has a new
property. if the Person class were final you would not be able to
do that. otherwise, you can.

Dynamic Class Instantiating

Similar Messages

Maybe you are looking for