Oc4j class-loading-heirarchy - enabling "search-local-classes-first" option

Guys,
I need some assistance with regards to oc4j class-loading hierarchy. Would appreciate some feedback on this...
Let me give you a bit of context first.
Basically we have 3 war modules which we initially were deployed separately on oc4j (transparently deployed by oc4j as ear). Now all of a sudden we have come to the need of instead bundling all the wars in one ear. The problem i started seeing is with respect to the output logs for the application, which was one per war modules initially (this was not clutter everything in one single log file and instead have one per deploy-able unit). The way this was implemented is that we had a log4j.properties bundled with each war with the output-file configuration, and since these 3 wars were deployed separately, the ear class-loader for each application would find one log4j.properties within each, and hence output-logs were generated as expected.
BUT now all of a sudden as we have changed the whole deployment structure, i.e. one EAR, all the application log-outputs are going to one single log file (instead of one for each war). My immediate impression was setting the "search-local-classes-first" would resolve this issue, since then the "web-module-class-loader" (one for each war) would come into play (which i believe doesn't otherwise) and would load/search for the resources/classes first (log4j.properties in our case) from the web-module (both in WEB-INF/lib and WEB-INF/classes folder) and if not found, only then it would give the job to the parent class-loader, which would be the ear-class-loader. But it doesnt seem like its working like that, since even after enabling this option, all logs are going to one log-output file, based on whichever war-module/log4j.properties is loaded first.
Thanks in advance and Regards,
Farhan.
Edited by: FarhanS on Nov 3, 2008 12:36 PM

Guys, i need some input here....
I turned on the class-loading trace and found out as to what is going on...but still wondering as to whats the reason for this behavior...
So basically browsing through the trace, gave me the following important segments (as below with my comments)....
1) Firstly, as the class-loading trace below, the log4j.jar is loaded up from the ear/lib directory (and hence by the ear-class-loader) and as it says the one in the web-inf/lib is ignored....Wonder why it picks up the one from ear/lib directory WHEN i have set the search-local-classes-first to "true", isn't the very purpose of the attribute to delegate the class-loading to the parent class-loader IFF the same is not found locally...
Code-source /oracle_apps/j2ee/portal/applications/wes-ear/wes-wicket-1.3.X-SNAPSHOT/WEB-INF/lib/log4j-1.2.15.jar (from WEB-INF/lib/ directory in /oracle_apps/j2ee/portal/applications/wes-ear/wes-wicket-1.3.X-SNAPSHOT/WEB-INF/lib)
has been ignored. It is a copy of /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib), which is already visible in the search path of
loader wes-ear.web.wes-wicket-1.3.X-SNAPSHOT:0.0.0. 2) Now on the other hand as you would see from the log-excerpts below, the log4j.properties resource file (with the log-output-file-name and all) is picked up from the very web-module class-loader, but as you would notice further, the log4j classes are initialized by the ear-loader itself with which the log4j classes are visible to all the other war-modules and hence don't even require re-initializing the log4j.properties...
====== THE RESOURCE CORRECTLY LOCATED BY THE WEB-CLASS-LOADER ======
Resource found: log4j.properties. Loader: wes-ear.web.wes-wicket-1.3.X-SNAPSHOT:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/wes-wicket-1.3.X-SNAPSHOT/WEB-INF/classes/
(from WEB-INF/classes/ in /oracle_apps/j2ee/portal/applications/wes-ear/wes-wicket-1.3.X-SNAPSHOT/WEB-INF/classes)
=== ALL THE Log4j CLASSES BELOW ARE BEING INITIALIZED/LOADED BY THE EAR-CLASS-LOADER =====
Class found: java.net.URL. Initiating loader: wes-ear.root:0.0.0. Defining loader: jre.bootstrap:1.5.0_06. Source: jre bootstrap
Class to be defined: org.apache.log4j.PropertyConfigurator (12024 bytes). Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class found: org.apache.log4j.PropertyConfigurator. Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class to be defined: org.apache.log4j.helpers.FileWatchdog (1875 bytes). Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class found: org.apache.log4j.helpers.FileWatchdog. Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class to be defined: org.apache.log4j.PropertyWatchdog (753 bytes). Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class found: org.apache.log4j.PropertyWatchdog. Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class found: java.io.InputStream. Initiating loader: wes-ear.root:0.0.0. Defining loader: jre.bootstrap:1.5.0_06. Source: jre bootstrap
Class found: java.io.FileInputStream. Initiating loader: wes-ear.root:0.0.0. Defining loader: jre.bootstrap:1.5.0_06. Source: jre bootstrap
Class found: java.util.Properties. Initiating loader: wes-ear.root:0.0.0. Defining loader: jre.bootstrap:1.5.0_06. Source: jre bootstrap
Class found: java.util.StringTokenizer. Initiating loader: wes-ear.root:0.0.0. Defining loader: jre.bootstrap:1.5.0_06. Source: jre bootstrap
Class to be defined: org.apache.log4j.Appender (676 bytes). Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class found: org.apache.log4j.Appender. Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class to be defined: org.apache.log4j.DailyRollingFileAppender (5724 bytes). Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)
Class to be defined: org.apache.log4j.FileAppender (4764 bytes). Loader: wes-ear.root:0.0.0. Source: /oracle_apps/j2ee/portal/applications/wes-ear/lib/log4j-1.2.15.jar (from application.xml <library-directory> in /oracle_apps/j2ee/portal/applications/wes-ear/lib)Thanks in advance and Regards,
Farhan.
Edited by: FarhanS on Nov 4, 2008 2:43 PM
Edited by: FarhanS on Nov 4, 2008 2:47 PM

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Guys,
I need some assistance with regards to oc4j class-loading hierarchy. Would appreciate some feedback on this...
Let me give you a bit of context first.
Basically we have 3 war modules which we initially were deployed separately on oc4j (transparently deployed by oc4j as ear). Now all of a sudden we have come to the need of instead bundling all the wars in one ear. The problem i started seeing is with respect to the output logs for the application, which was one per war modules initially (this was not clutter everything in one single log file and instead have one per deploy-able unit). The way this was implemented is that we had a log4j.properties bundled with each war with the output-file configuration, and since these 3 wars were deployed separately, the ear class-loader for each application would find one log4j.properties within each, and hence output-logs were generated as expected.
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if (resourceName.indexOf(".") != -1) {
resourceName =
resourceName.replaceAll("\\.", "/").replaceAll("/class", ".class");
//Use the ByteStreamClassLoader to load the class from byte array
byte[] classByteArray = null;
try {
classByteArray = getResourceBytes(resourceName);
catch (IOException ex1) {
throw new ClassNotFoundException(
"Could not load class data." + ex1.getMessage());
m_logger.log(
Level.FINEST, "Loading class '" +
name + "' Byte Length: " + classByteArray.length);
String p = definePackage(name);
c = defineClass(
name,
classByteArray,
0,
classByteArray.length,
ByteStreamClassLoader.class.getProtectionDomain());
m_cache.put(name, c);
if (resolve) {
resolveClass(c);
return c;

Hello everyone
I have run in to very strange behavior of JVM
I have created a class loader which allows my to load classes from
jar file, regardless that URLClassLoader supplies this functionality.
I am using this class loader to load some classes and call their virtual functions. The class diagram looks like that:
public interface I {
   public void init();
public class AAA implements
   public void init(){
public class BBB extends AAA{
   public void init(){
      //here comes implementation
}Interface I and class AAA are loaded with System Class loader and Class BBB is loaded using my class loader from jar file.
ByteStreamClassLoader classLoader = new ByteStreamClassLoader ();
Class cl = classLoader. loadClass(�com.product.BBB�,true);
I myInterface = cl.newInstance();
myInterface.init();The problem is that from some unknown reason java class AAA.init() instead of BBB.init().
Can somebody help me what am I doing wrong?
Class Loader code attached below
public class ByteStreamClassLoader   extends ClassLoader {
    protected HashMap m_cache = new HashMap();
    public void clearCashe() {
      m_cache = new HashMap();
    private String definePackage(String className) {
      StringBuilder strB = new StringBuilder();
      //Class name must be removed from the URI in order to define a package
      String[] packageArray = className.split("\\.");
      for (int i = 0; i < packageArray.length - 1; i++) {
        strB.append(packageArray).append(".");
String packageName = strB.toString();
packageName = packageName.substring(0, packageName.length() - 1);
if (getPackage(packageName) == null) {
m_logger.log(Level.FINEST, "Defining package '" + packageName + "'");
definePackage(packageName, null, null, null, null, null, null, null);
return packageName;
public synchronized Class loadClass(String name, boolean resolve) throws
ClassNotFoundException {
name = name.replaceAll("/", ".").replaceAll(".class", "");
//Try to locate the Class in cashe
Class c = (Class) m_cache.get(name);
//Try to locate the Class in the System Class Loader
if (c == null) {
try {
c = ClassLoader.getSystemClassLoader().loadClass(name);
catch (Exception ex) {}
else {
m_logger.log(Level.FINEST, "Class '" + name + "' found in cache");
//Load the class from byte array
if (c == null) {
String resourceName = name;
if (!resourceName.endsWith(".class")) {
resourceName = resourceName.concat(".class");
//Retrieve class byte representation
if (resourceName.indexOf(".") != -1) {
resourceName =
resourceName.replaceAll("\\.", "/").replaceAll("/class", ".class");
//Use the ByteStreamClassLoader to load the class from byte array
byte[] classByteArray = null;
try {
classByteArray = getResourceBytes(resourceName);
catch (IOException ex1) {
throw new ClassNotFoundException(
"Could not load class data." + ex1.getMessage());
m_logger.log(
Level.FINEST, "Loading class '" +
name + "' Byte Length: " + classByteArray.length);
String p = definePackage(name);
c = defineClass(
name,
classByteArray,
0,
classByteArray.length,
ByteStreamClassLoader.class.getProtectionDomain());
m_cache.put(name, c);
if (resolve) {
resolveClass(c);
return c;

Getting cl_abap_structdescr for method parameters of LOCAL classes?

Hi guys
I have a bit of a of a problem with getting an instance of the cl_abap_structdescr class for a method parameter type of a local class. The RTTI structure abap_parmdescr can only be used to diffrentiate between the basic built-in ABAP types and whether types are structures, tables or references. The question now arrives that once you have diffentiated that the parameter is a structure how do you determine the actual structure TYPE name for local classes to create an instance of the cl_abap_structdescr to continue your run-time analysis. For dictionary classes the parameter type name can be retrieved from the seosubcodf table, to me it looks as if one would have to resort to scanning the source code of local classes to arrive at the actual structure type name, but before I go to THAT kind of trouble I was wondering whether somebody out there might have a better solution for me. Your help would be grreatly appreciated and rewarded ;).
Kind regards
Ettienne Hugo

Hello Uwe
Thanks for your reply, I checked out the CL_OO_LOCAL_CLASSES class, unfortunately the class actually operates on the local classes declared for a dictionary class. I think to clarify my question I should point out that the parameters I'm trying to process are parameters that belong to classes that are defined and implemented using include programs, these include programs would then typically be used in Function Groups to construct applications so the classes that I refer to are actually not in any way related to dictionary classes. The cl_abap_classdescr class works fine on these types of classes when you refer to them using the "\PROGRAM=my_program\CLASS=my_class" format with the describe_by_name method, unfortunately the class just does not provide sufficient information for structure type parameters to actually construct them during run-time...
Stay well
Ettienne

Dynamic class loading from JARs in web application

Hello,
I'm working on a web project in which we would like to dynamically load plugins without server restart.
We have developed our own ClassLoader in order to load the plugins from a path or with a user interface upload function.
The class loader hierarchy should be something like this:
      Bootstrap
          |
       System
          |
       Common
Catalina   Shared
        Webapp1 OurSystem
                   PluginClassLoaderThe all works fine within the classes loaded in the PluginClassLoader, but classes loaded in OurSystems class loader cannot access classes loaded in PluginClassLoader. For example when Hibernate tries to load classes definied in mapping files we got a java.lang.ClassNotFoundException.
Is there a way to load classes dynamically to OurSystems class loader or notify it about PluginClassLoaders classes?
Or is this a bad way to do it?
Best regards,
Kristoffer Renholm

Hi,
Sounds like a classpath problem that the folks in the workshop newsgroup
could help with. Try asking your question in:
http://newsgroups.bea.com/cgi-bin/dnewsweb?cmd=xover&group=weblogic.developer.interest.workshop&utag=
Bruce
Graeme Dougal wrote:
>
Hi, I am developing a web service with weblogic workshop. The JWS file references
other classes one of which is a factory for distributing various implementations
of an interface. I am trying to dynamically load the relevant class to be distributed
from the factory via its name, e.g. Class c = Class.forName(className)
However I keep getting a classNotFoundException.
Any ideas ??

Dynamic Class Loading in an EJB Container

Hello,
We have a need to load classes from a nonstandard place with in an ejb container, ie a database or secure store. In order to do so we have created a custom class loader. Two issues have come up we have not been able to solve, and perhaps some one knows the answer to.
Issue 1.
Given the following code:
public static void main(String args[])
MyClassLoader loader = new MyClassLoader("lic.dat");
System.out.println("Loading class ..." + "TestObject");
Object o = Class.forName("TestObject",true,loader).newInstance();
System.out.println("Object:" + o.toString());
TestObject tstObj = (TestObject) o;
tstObj.doIt();
What happens when executed is as follows. Class.forName calls our loader and does load the class as we hoped, it returns it as well, and the o.toString() properly executes just fine. The cast of the object to the actual TestObject fails with a class not found exception. We know why this happens but don't know what to do about it. It happens because the class that contains main was loaded by the system class loader (the primordial class loader as its sometimes called), That class loader does not know about TestObject, so when we cast even though the class is "loaded" in memory the class we are in has no knowledge of it, and uses its class loader to attempt to find it, which fails.
> So the question is how do you let the main class know to use our class loader instead of
the system class loader dispite the fact is was loaded by the system class loader.
Issue 2:
To make matters worse we want to do this with in an EJB container. So it now begs the question how do you inform an EJB container to use a specific class loader for some classes?
Mike...

Holy crap! We are in a similar situation. In creating a plugin engine that dynamically loads classes we use a new class loader for each plugin. The purpose is so that we can easily unload and/or reload a class at runtime. This is a feature supposedly done by J2EE app servers for hot-deploy.
So our plugins are packaged as JAR files. If you put any class in the CLASSPATH, the JVM class loader (or the class loader of the class that is loading the plugin(s)), will load the class. The JavaDoc API states that the parent classloader is first used to see if it can find the class. Even if you create a new URLClassLoader with NULL for parent, it will always use the JVM class loader as its parent. So, ideally, in our couse, plugins will be at web sites, network drives, or outside of the classpath of the application and JVM.
This feature has two benefits. First, at runtime, new updates of plugins can be loaded without having to restart the app. We are even handling versions and dependencies. Second, during development, especially of large apps that have a long startup time, being able to reload only one plugin as opposed to the annoying startup time of Java apps is great! Speeds up development greatly.
So, our problem sounds just like yours. Apparently, the Client, which creates an instance of the plugin engine, tries to access a plugin (after the engine loades it via a new classloader instance for each plugin). Apparently, it says NoDefClassFound, because as you say, the client classloader has no idea about the plugin class loaded by another classloader.
My co-developer came up with one solution, which I really dont like, but seems to be the only way. The client MUST have the class (java .class file) in its classpath in order to work with the class loaded by another class loader. Much like how in an EJB container, the web server calling to EJB MUST contain the Home and Remote interface .class files in its classpath, the same thing needs to be done here. For us, this means if a plugin depends on 5 others, it must contain ALL of the .class files of those plugins it depends on, so that the classloader instance that loads the plugin, can also see those classes and work with them.
Have you got any other ideas? I really dislike that this has to be done in this manner. It seems to me that the JVM should be able to allow various class loaders to work with one another in such a way that if a client loaded by one classloader has an import statement in it to use a class, the JVM should be able to fetch the .class out of the other classloader and share it, or something!
This seems to me that there really is no way to actually properly unload and then reload a class so that the JVM will discard and free up the previous class completely, while using the new class.
I would be interested in discussing this topic further. Maybe some others will join in and help out on this topic. I am surprised there isn't a top-level forum topic about things like class loaders, JVM, etc. I wish there was a way to add one!

WebSphere class loading issue

Hi,
We ran into this issue and have been trying to resolve since yesterday with no luck. I'm wondering if anybody else has encountered this and has any thoughts ...
We are trying to call the methods of the com.ibm.websphere.runtime.ServerName class in a utility class that is packaged into a jar and put onto the JVM classpath in WebSphere 6.1. And we are running into NoClassDefFound errors. So we just did Class.forName("com.ibm.websphere.runtime.ServerName") in that utility class and got the ClassNotFoundException as expected. But when we do the same in a separate utility class that is outside of the classpath, both the forName and the actual method calls work without any problem.
That kind of suggested that the com.ibm.websphere.runtime.ServerName class is not "available"(/loaded) by the time our utility class gets loaded, may be. So we turned on the Verbose Class Loading to see the order in which the classes are loaded when the JVM starts up. But the com.ibm.websphere.runtime.ServerName class is loaded way before our utility class from the jar in the classpath.
So I'm wondering:
Why would it give me a ClassNotFound exception in my utility class (which is put on the classpath) when the log shows that the utility class is already loaded by the time this class starts loading?
Any feedback or thoughts would be greatly appreciated.
Thanks,
Bharathi

Java_Unlimited wrote:
We could figure out the answer from your responses, thank you guys!
It is true that our jar is being loaded by a different class loader, to which the ServerName class is not available. Also in one of the articles quoted in the responses, it mentioned specifying the jar in the ws.ext.dirs property, not in the classpath for the ws ext classes to be available to the jar. And that fixed the problem. We defined a custom property ws.ext.dirs and put the jar file in there.
Thanks everyone!
Edited by: Java_Unlimited on Feb 6, 2009 10:42 AMBharati, we're glad to help and thanks for lettings us know what you did to make it work.

Oc4j class-loading-heirarchy - enabling "search-local-classes-first" option

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