4.2. Debug Migration Issues

1. First, try to find the missing dependency. This is described in more detail here: Section 4.2.3, “Find the JBoss Module Dependency”
2. If there is not a module for the missing class, find the JAR in the previous install. For more information, see Section 4.2.4, “Find the JAR in the Previous Install”

Procedure 4.5. Find the Dependency

1. First determine if there is an obvious module for the class.
   1. Navigate to the EAP_HOME/modules/system/layers/base/ directory and look for the module path matching class named in the ClassNotFoundException.
      You find the module path org/apache/commons/logging/.
   2. Open the EAP_HOME/modules/system/layers/base/org/apache/commons/logging/main/module.xml file and find the module name. In this case, it is "org.apache.commons.logging".
   3. Add the module name to the Dependencies in the MANIFEST.MF file:

      Manifest-Version: 1.0
      Dependencies: org.apache.commons.logging
      

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2. If there is no obvious module path for the class, you may need to find the dependency in another location.
   1. Find the class named by the ClassNotFoundException in the Tattletale report.
   2. Find the module containing the JAR in the EAP_HOME/modules directory and find the module name as in the previous step.

1. Open a terminal and navigate to the EAP5_HOME/ directory.
2. Issue the command:
   grep 'org.hibernate.validator.ClassValidator' `find . \-name '*.jar'`
3. You might see more than one result. In this case, the following result is the JAR we need:

   Binary file ./jboss-eap-5.1/seam/lib/hibernate-validator.jar matches

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4. Copy this JAR to the application's lib/ directory.
   If you find that you need a large number of JARs, it may be easier to define a module for the classes. For more information, see Modules in the chapter entitled Get Started Developing Applications in the Development Guide for JBoss EAP 6 on https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/?version=6.4.
5. Rebuild and redeploy the application.

1. Search the application to find all JAR(s) that contain the class named by the ClassCastException. If there is a module defined for the class, find and remove the duplicate JAR(s) from the application's WAR or EAR.
2. Find the JBoss module containing the class and explicitly define the dependency in the MANIFEST.MF file or in the jboss-deployment-structure.xml file. For more information, see Class Loading and Subdeployments in the chapter entitled Class Loading and Modules in the Development Guide for JBoss EAP 6 on https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/?version=6.4.
3. If you are not able to resolve it using the steps above, you can often determine the cause of the problem by printing the class loader information to the log. For example, you see the following ClassCastException in the log:

   java.lang.ClassCastException: com.example1.CustomClass1 cannot be cast to com.example2.CustomClass2

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   1. In your code, print the class loader information for the classes named by the ClassCastException to the log, for example:

      logger.info("Class loader for CustomClass1: " + 
            com.example1.CustomClass1.getClass().getClassLoader().toString());
      logger.info("Class loader for CustomClass2: " + 
            com.example2.CustomClass2.getClass().getClassLoader().toString());
      

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   2. The information in the log shows which modules are loading the classes and, based on your application, you need to remove or move the conflicting JAR(s).

1. Expand the Component section on the page and look for the org.jboss.seam.caughtException component.
2. The cause and stack trace should point you to the missing dependencies.
   

   Figure 4.2. Component org.jboss.seam.caughtException information

3. Use the technique described in Section 4.2.2, “Debug and Resolve ClassNotFoundExceptions and NoClassDefFoundErrors” to resolve module dependencies.
   In the example above, the simplest solution is to add org.slf4j to the MANIFEST.MF

   Manifest-Version: 1.0
   Dependencies: org.slf4j
   

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   Another option is to add a dependency for the module to the jboss-deployment-structure.xml file:

   <jboss-deployment-structure>
      <deployment>
           <dependencies>
             <module name="org.slf4j" />
           </dependencies>
       </deployment>
   </jboss-deployment-structure>

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