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How to find all classes with my annotation | Wildfly JavaEE

What is the best way to find all classes with a specific annotation in a JavaEE deployment? I work with a WildFly ApplicationServer and have created my own annotation. At the start of my deployment I would like to find all classes with my annotation and cache them for later access. What do I have to do to protect resources?

First of all Wildfly has modular class loading structure. In Wildfly doc:
Since JBoss AS 7, Class loading is considerably different to previous versions of JBoss AS. Class loading is based on the JBoss Modules project. Instead of the more familiar hierarchical class loading environment, WildFly's class loading is based on modules that have to define explicit dependencies on other modules. Deployments in WildFly are also modules, and do not have access to classes that are defined in jars in the application server unless an explicit dependency on those classes is defined.
As described above, if you have more .ear or .war package, they cannot see classes within each other unless explicit dependency defined. Each module can see its own class therefore each module should load and cache its own classes. You can not load all classes with a single class and single method.
With the following code you can see all loaded classes in the module.
Field f = ClassLoader.class.getDeclaredField("classes");
f.setAccessible(true);
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
Vector<Class> classes = (Vector<Class>) f.get(classLoader);

How does Java runtime find my main class?

I am learning Spring Boot. I made a simple Spring Boot project that can output a hello world string at http://localhost:8080/welcome
I use Maven to build my project that would output a jar file.
To start up my spring boot app, I use the command as below
java -jar my-springboot-app.jar
My question is:
How is java smart enough to locate my main class and its main method (e.g. the application launcher)?
I checked the jar file and browsed those BOOT-INF & META-INF and could not find any clues.
Does the spring boot framework (#SpringBootApplication) or maven automatically do the magic for me?

In case of spring boot jar the things are little bit more complicated than regular jar. Mainly because spring boot applicaton jar is not really a JAR (by jar I mean something that has manifest and compiled classes). Regular JARs can be "recognized" and processed by jvm, however in Spring Boot there are also packed dependencies (take a look at BOOT-INF/lib) so its jars inside JARs. How to read this?
It turns out that spring boot always has its own main class that is indeed referred to in MANIFEST.MF and this a real entry point of the packaged application.
The manifest file contains the following lines:
Main-Class: org.springframework.boot.loader.JarLauncher
Start-Class: com.example.demo.DemoApplication
Main-Class is a JVM entry point. This class, written by spring developers, basically does two things:
- Establishes a special class loader to deal with a "non-regular-jar" nature of spring boot application. Due to this special class loaders spring boot application that contains "jars" in BOOT-INF/lib can be processed, for example, regular java class loaders apparently cannot do this.
- Calls the main method of Start-Class value. The Start-Class is a something unique to spring boot applications and it denotes the class that contains a "main" method - the class you write and the class you think is an entry point :) But from the point of view of the spring boot infrastructure its just a class that has an "ordinary" main method - a method that can be called by reflection.
Now regarding the question "who builds the manifest":
This MANIFEST.MF is usually created automatically by plugins offered by Spring Developers for build systems like Maven or Gradle.
For example, the plugin looks like this:
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
During its work, this plugin identifies your main class (com.example.demo.DemoApplication in my example). This class is marked with #SpringBootApplication annotation and has a public static void main method.
However, if you put many classes like this the plugin probably won't recognize the correct class so you'll need to configure the plugin properties in POM.xml to specify the right class.

Java classes are executed within a larger context,
you run java -jar somejar.jar the class in question will be selected in the .jar file's manifest.
#SpringBootApplication will have componentscan, enabling auto configuration(autowired)
componentscan - to identify all the controller, service and configuration classes within the package.

How to specify order of JAR class loading in weblogic

I have an EAR file that contains two different jars that share some classes with an identical package.class name. These JARs are deployed in my APP-INF/lib directory.
Let's say A jar contains the latest version of classes and B contains the old version of classes. When a class is referenced Weblogic looks first into B jar and loads the old version which break some functionality.
How can I tell Weblogic to load jar A before B from APP-INF/lib? I need to define a specific order to avoid loading old classes.
I have already tried adding A jar to <classloader-structure> in weblogic-application.xml like so:
EAR structure:
EAR
\--->A.jar
\--->webapp.war
.....
weblogic-application.xml:
<classloader-structure>
<module-ref>
<module-uri>A.jar</module-uri>
</module-ref>
.......
</classloader-structure>
but then it throws error saying
weblogic.management.DeploymentException: classloader-structure element in weblogic-application.xml is referencing the module-uri A.jar which does not exist in this application.
Also one thing to remember is that A.jar is not a module, war or EJB it just a plain hibernate library: hibernate-jpa-2.0-api-1.0.1.Final.jar
I am using Weblogic 12c version.

You need to set parent last strategy for class-loader, refer http://www.rgagnon.com/javadetails/java-0551.html, as i remember there is a GUI in weblogic server to do the same.

NoSuchMethodError - Calling Class/Method from Class in Same Package

We are integrating an internal framework into our weblogic application and we are running into deployment problems.
Technologies Used
Weblogic 10.3.6 application
Spring 3.0
Maven 2
Eclipse J2EE
The Problem
On startup of the weblogic application, we receive the following NoSuchMethodError while initializing one of the beans. This error is occuring when calling classes in the org.joda.time (2.0) jar.
Caused By: java.lang.NoSuchMethodError: org.joda.time.DateTimeZone.convertLocalToUTC(JZ)J
at org.joda.time.LocalDate.toDateTimeAtStartOfDay(LocalDate.java:715)
at org.joda.time.LocalDate.toDateTimeAtStartOfDay(LocalDate.java:690)
. . . excluded . . .
Things We Have Tried
After Googling "NoSuchMethodError spring", many of the problems seem to be incompatible Spring versions. After printing the dependency tree, the only Spring version in use is 3.0.
Googling "NoSuchMethodError" usually gave JAR hell solutions.
Multiple versions of the same dependency. After doing some maven dependency management, the only joda-time jar in use is 2.0. Additionally, the local repository was purged of any unnecessary jars.
.war / runtime may not have the correct jars included in the lib directory. After looking into the WEB_INF/lib directory, the only joda-time jar is version 2.0, which contains all of the appropriate class files
One mysterious thing is that the DateTimeZone.convertLocalToUTC(JZ)J has been a part of the org.joda.time project since 1.0, so even if we have incompatible versions, the method should still be found, especially if the class and package are able to be found.
Finally there are no other DateTimeZone classes in the project (ctrl+shift+T search in eclipse) so I'm confused as to which class is being loaded if the org.joda.DateTimeZone class is not being loaded.
Questions:
Can anyone explain why the method could not be found?
Are there more places to check for existing or conflicting jars?
Is there a way to check the DateTimeZone class that the LocalDate class is using during runtime via Eclipse debug?

Here's some interesting reading:
prefer-web-inf-classes Element
The weblogic.xml Web application deployment descriptor contains a
element (a sub-element of the
element). By default, this element is set to
False. Setting this element to True subverts the classloader
delegation model so that class definitions from the Web application
are loaded in preference to class definitions in higher-level
classloaders. This allows a Web application to use its own version of
a third-party class, which might also be part of WebLogic Server. See
“weblogic.xml Deployment Descriptor Elements.”
taken from: http://docs.oracle.com/cd/E15051_01/wls/docs103/programming/classloading.html
Other troubleshooting tips:
You can try: -verbose:class and check your managed server's logs to check if the class is being loaded properly.
An efficient way to confirm which intrusive jar might be getting loaded is by running a whereis.jsp within the same webcontext (i.e., JVM instance) of this app.
--whereis.jsp --
<%# page import="java.security.*" %>
<%# page import="java.net.URL" %>
<%
Class cls = org.joda.time.DateTimeZone.class;
ProtectionDomain pDomain = cls.getProtectionDomain();
CodeSource cSource = pDomain.getCodeSource();
URL loc = cSource.getLocation();
out.println(loc);
// it should print something like "c:/jars/MyJar.jar"
%>
You can also try jarscan on your $WEBLOGIC_HOME folder to see if you can find the jar that contains this class: https://java.net/projects/jarscan/pages/Tutorial

A NoSuchMethodError is almost always due to conflicting library versions. In this case I'm guessing there are multiple versions of joda libraries in the two projects.
Weblogic is pulling the org.joda jar.
Tryu adding this in your weblogic.xml to exclude the jar that weblogic is pulling, and instead use your appllication jar.
The below is from my application, you can have a look what all we have to removed for our application.
<wls:container-descriptor>
<wls:prefer-application-packages>
<wls:package-name>antlr.*</wls:package-name>
<wls:package-name>org.slf4j.*</wls:package-name>
<wls:package-name>org.slf4j.helpers.*</wls:package-name>
<wls:package-name>org.slf4j.impl.*</wls:package-name>
<wls:package-name>org.slf4j.spi.*</wls:package-name>
<wls:package-name>org.hibernate.*</wls:package-name>
<wls:package-name>org.springframework.*</wls:package-name>
<wls:package-name>javax.persistence.*</wls:package-name>
<wls:package-name>org.apache.commons.*</wls:package-name>
<wls:package-name>org.apache.xmlbeans.*</wls:package-name>
<wls:package-name>javassist.*</wls:package-name>
<wls:package-name>org.joda.*</wls:package-name>
<wls:package-name>javax.xml.bind.*</wls:package-name>
<wls:package-name>com.sun.xml.bind.*</wls:package-name>
<wls:package-name>org.eclipse.persistence.*</wls:package-name>
</wls:prefer-application-packages>
<wls:show-archived-real-path-enabled>true</wls:show-archived-real-path-enabled>
</wls:container-descriptor>

Classloader problem with EJB

I'm working on a project which includes persistence library (JPA 1.2), EJB 3 and Web presentation layer (JSF). I develop application using Eclipse and application is published on Websphere Application Server Community Edition (Geronimo 2.1.4) through eclipse plugin (but the same thing happens if I publish manually). When publishing to server I get the following error:
java.lang.NoClassDefFoundError: Could not fully load class: manager.administration.vehicles.VehicleTypeAdminBean
due to:manager/vehicles/VehicleType
in classLoader:
org.apache.geronimo.kernel.classloader.TemporaryClassLoader#18878c7
at org.apache.xbean.finder.ClassFinder.(ClassFinder.java:177)
at org.apache.xbean.finder.ClassFinder.(ClassFinder.java:146)...
In web.xml I have reference to EJB:
<ejb-local-ref>
<ejb-ref-name>ejb/VehicleTypeAdmin</ejb-ref-name>
<ejb-ref-type>Session</ejb-ref-type>
<local>manager.administration.vehicles.VehicleTypeAdmin</local>
<ejb-link>VehicleTypeAdminBean</ejb-link>
</ejb-local-ref>
EJB project has a reference to persistence project, and Web project has references to both projects. I don't get any compilation errors, so I suppose classes and references are correct.
I don't know if it is app server problem, but I ran previously application on the same server using same configuration parameters.
Does anybody have a clue what might be the problem?

Looks almost like it couldn't find the class manager.vehicles.VehicleType when it was attempting to create/load the class manager.administration.vehicles.VehicleTypeAdminBean.
I've encountered similar problems before. When the class loader attempts to load the class it looks at the import statements (and other class usage declarations) and then attempts to load those classes and so on until it reaches the bottom of the chain (ie java.lang.Object). If it cannot find one class along the chain (in your case it looks like it cannot load VehicleType) then it will state that it cannot load the class at the top of the chain (in your case VehicleTypeAdminBean).
Is the VehicleType class in a different jar? If you have a web module and and EJB module do you have the jar containing the VehicleType class in the appropriate place(s). Sometimes with web projects you have to put the jars in the WebContent/WEB-INF/lib folder or it won't find them.
Are both of these projects deployed separately (ie. two ears? or one ear and one war?) or are they together (ie, one ear with jars and a war inside?). I'm assuming the second given you declared your EJB local?
The jars that you are dependent on also have to be declared in your MANIFEST.MF files in the projects that use it.
I'm kind of running on guesses since I do not know your project structure. Showing that would help quite a bit. But I'd still check on where VehicleType is located with regards to your EJB class. You might find it isn't where you think it is come packaging or runtime.

Thanks #Chris for WebContent/WEB-INF/lib idea ! it works for me by following these steps :
1- Export my EJBs to a JAR (MyEJBs.jar)
2- I created another jar with your_installation_path/IBM/SDP/runtimes/your_version/binCreateEJBStrub.bat via CMD.exe, by executing this command :
createEJBStubs.bat <my_path>/MyEJBs.jar -newfile –quiet
3- A new jar will be automatically created in the same directory as MyEJBs.jar named MyEJBs_withStubs.jar
4- Put your new jar in WebContent/WEB-INF/lib
5- Call your EJBs by :
MyEJBRemote eJBRemote;
InitialContext ic = new InitialContext();
obj = ic.lookup("your_ejb_name_jndi");
eJBRemote = (MyEJBRemote ) PortableRemoteObject.narrow(obj,
MyEJBRemote.class);
eJBRemote = (MyEJBRemote ) obj;
Now you can call your EJBs from another EAR