I am deploying two war say A,B in Java EE Server say Jboss.
Deployment order will be
WAR A
WAR B
I need to call a method once war B is deployed. That method will create an instance of a class which will be loaded only from the class path mentioned in the manifest file of the war.
I used a ServletContextListener, but this failed.
Note : I tested ServletContextListener - by specifying a sample content in the static block of the class that has to be instantiated and tried to create an instance from the ServletContextListener. But an error is thrown stating "RunTime Exception unable to load the class", and the sample content is also not displayed. More over the class is loaded in the server which is confirmed via -verbose:class option in the JAVA_OPTS.
But it works if I load the class from war A. It even works fine. It's a big process to explain why there is a need for creating such instances. I don't want to change the way in which the instance of the class is created.
Is there any other way to call the method after the war and all its dependencies are completely loaded?
Related
I developer a web application using Java. When I deploy it to my application server (Jetty, Tomcat, JBoss, GlassFish, etc.) throws an error. I can see this error message in the stacktrace:
java.lang.ClassNotFoundException
Or
java.lang.NoClassDefFoundError
What does this mean and how can I fix it?
What does this mean?
First, let's see the meaning of java.lang.ClassNotFoundException:
Thrown when an application tries to load in a class through its string name using:
The forName method in class Class.
The findSystemClass method in class ClassLoader.
The loadClass method in class ClassLoader.
but no definition for the class with the specified name could be found.
Usually, this happens when trying to open a connection manually in this form:
String jdbcDriver = "...'; //name of your driver
Class.forName(jdbcDriver);
Or when you refer to a class that belongs to an external library and strangely this class cannot be loaded when the application server tries to deploy the application.
Let's see the meaning of java.lang.NoClassDefFoundError (emphasis mine):
Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.
The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found.
The last part says it all: the class existed at compile time i.e. when I compiled the application through my IDE, but it is not available at runtime i.e. when the application is deployed.
how can I fix it?
In Java web applications, all third party libraries used by your application must go in WEB-INF/lib folder. Make sure that all the necessary libraries (jars) are placed there. You can check this easily:
- <webapp folder>
- WEB-INF
- lib
+ jar1
+ jar2
+ ...
- META-INF
- <rest of your folders>
This problem usually arises for JDBC connectivity jars (MySQL, Derby, MSSQL, Oracle, etc.) or web MVC frameworks libraries like JSF or Spring MVC.
Take into account that some third party libraries rely on other third party libraries, so you have to add all of them in WEB-INF/lib in order to make the application work. A good example of this is RichFaces 4 libraries, where you have to download and add the external libraries manually.
Note for Maven users: you should not experience these problems unless you have set the libraries as provided, test or system. If set to provided, you're responsible to add the libraries somewhere in the classpath. You can find more info about the dependency scopes here: Introduction to the Dependency Mechanism
In case the library must be shared among several applications that will be deployed on your application server e.g. MySQL connector for two applications, there's another alternative. Instead of deploying two war files each with their own MySQL connector library, place this library in the common library folder of the server application, this will enable the library to be in the classpath of all the deployed applications.
This folder vary from application server.
Tomcat 7/8: <tomcat_home>/lib
JBoss 7/Wildfly: <jboss_home>/standalone/lib
The class must exist under WEB-INF/classes or be inside a .jar file under WEB-INF/lib. Make sure it does.
Same problem happen with me.
Might be possible one of your libraries are using some classes internal which is not available
in your lib or maven dependency pom.xml.
Thats means you have analyze your error logs and identify these classes and then import all dependencies in maven or lib folder.
I have fixed this error by the same way.
because some of my libraries are using activation.jar and json.jar internally.
I use GlassFish 4 web profile and I have the following interface and class.
#Local
public interface SomeService {
...
}
#Singleton
public class SomeServiceBean implements SomeService {
...
}
When I put interface and class in .war archive (that is in domain1/autodeplay) everything works fine. However, when I put interface and class in separate .jar archive (that is in domain1/lib) then deploying war application I get:
java.lang.RuntimeException: Cannot resolve reference Local ejb-ref name=com.temp.MyServlet/someService,Local 3.x interface =com.temp.SomeService,ejb-link=null,lookup=,mappedName=,jndi-name=,refType=Session
at com.sun.enterprise.deployment.util.ComponentValidator.accept(ComponentValidator.java:374) ~[dol.jar:na]
at com.sun.enterprise.deployment.util.DefaultDOLVisitor.accept(DefaultDOLVisitor.java:78) ~[dol.jar:na]
at com.sun.enterprise.deployment.util.ComponentValidator.accept(ComponentValidator.java:123) ~[dol.jar:na]
at com.sun.enterprise.deployment.util.ApplicationValidator.accept(ApplicationValidator.java:152) ~[dol.jar:n
...
I don't use any xml descriptors. So, is it possible to have EJBs in domain1/lib and if yes, how to make EJB container find them? P.S. I tried in GF 4 full - result is the same.
EJBs cannot be added as a library to GlassFish, libraries are just added to the classpath and any annotations on them are ignored and they do not go through the EJB container. If you do want your EJBs as a seperate JAR, they can be deployed just like a WAR or EAR file.
In the Glassfish reference manual for the add-library command it says that it "adds the library to the class loader directory", while for the deploy command it says that "Applications can be...EJB modules".
Also by looking at the source code for Glassfish it can be worked out that all libraries are simply added to the Classloader either at launch (See here and here) or if in applibs then when the application is deployed (See here).
I'm trying to extend webapp functionality without redeploying webapp archive. App runs under Glassfish 3.
Basically, what I did is the following:
webapp.war contains some part.jar which is a part of webapplication. It contains some class SomeClass. Webapp allows some custom configuration where descendant of SomeClass may be loaded dynamically using Class.forName.
I derived ExtensionClass from SomeClass (ExtensionClass extends SomeClass), compiled it using part.jar and got some extension.jar.
I tried to put extension.jar into domain/lib and domain/lib/ext. But then app when loading ExtensionClass says java.lang.NoClassDefFoundError: SomeClass (note that it says about parent class). It seems that classloader which loads library cannot find the base class, which is contained in the webapp.
Goal: I'd like to extend app using dependencies from it but without rebuilding.
Question: what can be done in this case?
Edit
If I just put my extension.jar into applications/mywebapp/WEB-INF/libs it obviously works, as if I'd put it into webapp.war itself. But it is very dirty, I want to solve it without doing this dirtiness and without touching webapp.war.
I have worked on implementation of the Entity remote service.
I have created one custom service method in EntityServiceImpl,Created custom service method providing service through InstitutionServiceUtil.
After deploy the portlet, while sending request to service method through from browser window,I am getting below Exception
exception":"java.lang.ClassCastException: com.institutions.model.impl.InstitutionImpl
cannot be cast to com.institutions.model.Institution
Note: If I send the request after restart the server, I didn't get above exception.
How to resolve the above Exception?
I assuming that InstitutionImpl implements the interface Institution. If so, then the root cause of the exception is classloading: Classloader A did load Institution but InstitutionImpl was loaded from a different classloader. Two classes in Java are only equivalent if the fully qualified name and the classloader are the same.
I don't know enough about liferay to tell you how it's class loading works. But to solve the problem, you need to find out if the Institution interface could already be around when you try to load your implementation (maybe from a previous deployment attempt).
While deploying the portlets that throws the class cast exception, do the following:
deploy the application in the liferay/deploy.
shutdown the liferay
move the service jar from the WEB-INF/lib from the portlet to the /lib/ext of the tomcat
remove the temp and work folder from the tomcat
restart the tomcat.
OR ...what worked for me was
change the package name while building the service.xml in the service.xml file
Or if you have already built the service, do these steps
Just delete the 5 packages that are created from the service builder,
i.e
model.impl
service.base
service.http
service.impl
service.persistence
delete the .xml generated in the META-INF folder except for the file ext-spring.xml
delete the XX-service.jar from the docroot/lib folder
delete the service folder in the docroot folder.
change the package name in the service.xml and build the path.
I have two war file app1.war and app2.war deployed in a single JBoss instance. Package names for java classes for both war files starts with com.myapp
To add further, there are some Classes that are common between the two apps while there are some that have same fully qualified class names but are different (Source Code has changed).
I want to know, if this could pose threat of any kind to the deployment scenario?
You could get class loading problems if your applications are not isolated, i.e. have their own class loading repository and class loaders. If you configure JBoss to isolate the applications from each other you should be fine (I don't know what is the default for your version but 4.2.3 that we use does not isolate apps by default).
To clarify that a bit:
If you have two classes with different implementations but the same FQCN you could get the wrong class from the class loader for the application that is loaded second. Even if the implementation was the same you could get class cast exceptions or other strange behavior if one app gets the class from the other app.
I had a similar situation with multiple apps.Look at my solution here
Best way is to isolate class loading for your application archives.
For JBoss 5.1.0 GA following worked for me.
Create jboss-classloading.xml file in WEB-INF folder.
Added following lines to this file
Here,
export-all="NON_EMPTY" => Makes sure the classes loaded for this app is not exported
import-all="true" => Imports and uses all of the class definition available.
parent-first="false" => If more than one class with same name is found, one defined under the application will be used first.
FYI. This also helped me embedding the log configuration of log4j in the application war file. Will need to place log4j.xml in WEB-INF/classes and have a log4j.jar in WEB-INF/lib folder.
There will be one class loader instance for each application or standalone module. In other words, classes in app1.war will be loaded in different class loader than the classes in app2.war. This is the default behavior of any Java EE server; So it really doesn't matter about having classes with the same package/names and/or different content. This is the default behavior of any Java EE server.
Having said that, if you tweak the class loader policy of the server or try to load classes (reflect) using anything other than Thread.currentThread().getContextClassLoader(), you could be asking for trouble.