1 Reply Latest reply on Apr 10, 2015 4:45 AM by Andrew Dinn

    Reflection to call Java method from Application from Helper Class

    John Martin Newbie

      Hi,

       

      Suppose my application has Class structure like

       

      package A;

      Class B

      {

          void method()

           {  }

      }

       

      My User defined Helper Class want to Access method from Class B using Reflection but it throws Exception at

      Class.forName("A.B"); as ClassNotFoundException.

       

      Thanks in advance,

       

      Regards,

      John

        • 1. Re: Reflection to call Java method from Application from Helper Class
          Andrew Dinn Master

          Hi John,

           

          Hmm, seems like you already tried to follow the advice I just posted in response to your last note.

           

          My User defined Helper Class want to Access method from Class B using Reflection but it throws Exception at

          Class.forName("A.B"); as ClassNotFoundException.

           

          Class.forName uses its caller's classloader to resolve the class lookup. If your helper is in the bootstrap or system classpath then this will only find a class that is also in the bootstrap or system classpath, respectively.

           

          There are two things you can do to allow your helper to find the required class:

           

          1) use the target class's classloader to the lookup the class you need by calling Classloader.findClass(String). Here is one way of providing the helper method with the required loader

           

          RULE helper rule
          CLASS org.my.app.TargetClass
          METHOD org.my.app.TargetMethod
          AT ENTRY
          HELPER org.my.helper.MyHelper
          BIND target = $0.getClass()
               loader = target.getClassLoader()
          IF TRUE
          DO helperDoReflectiveCall($1, $2, loader)
          ENDRULE
          

           

          You helper method will need to call loader.findClass("com.mysql.jdbc.Driver") to lookup the desired class.

           

          2) Just refer to the desired class by name in the rule and pass it into the helper call. Class literals are perfectly legitimate Byteman rule expressions. They are resolved using the loader of the target class:

           

          RULE helper rule
          CLASS org.my.app.TargetClass
          METHOD org.my.app.TargetMethod
          AT ENTRY
          HELPER org.my.helper.MyHelper
          IF TRUE
          DO helperDoReflectiveCall($1, $2, com.mysql.jdbc.Driver.class)
          ENDRULE