carlos@Carlos-PC:/opt/ros/electric/ros$ rosrun rosjava_tutorial_pubsub java_msgs.py my_pkg/bin/org/ros/rosjava_tutorial_pubsub/Listener.class 
generating messages for package [my_pkg/bin/org/ros/rosjava_tutorial_pubsub/Listener.class]
Traceback (most recent call last):
  File "/opt/ros/electric/ros/rosjava/rosjava_tutorial_pubsub/java_msgs.py", line 661, in <module>
    generate_messages(sys.argv)
  File "/opt/ros/electric/ros/rosjava/rosjava_tutorial_pubsub/java_msgs.py", line 657, in generate_messages
    output_dir = generate(p, output_dir=options.output_dir)
  File "/opt/ros/electric/ros/rosjava/rosjava_tutorial_pubsub/java_msgs.py", line 630, in generate
    pkg_dir = roslib.packages.get_pkg_dir(package)
  File "/opt/ros/electric/ros/core/roslib/src/roslib/packages.py", line 220, in get_pkg_dir
    raise InvalidROSPkgException("Cannot locate installation of package %s: %s. ROS_ROOT[%s] ROS_PACKAGE_PATH[%s]"%(package, rperr.strip(), ros_root, ros_package_path))
roslib.packages.InvalidROSPkgException: Cannot locate installation of package my_pkg/bin/org/ros/rosjava_tutorial_pubsub/Listener.class: [rospack] couldn't find package [my_pkg/bin/org/ros/rosjava_tutorial_pubsub/Listener.class]. ROS_ROOT[/opt/ros/electric/ros] ROS_PACKAGE_PATH[/home/carlos/ros_workspace:/opt/ros/electric/stacks:/opt/ros/electric/rosjava_core:/opt/ros/electric/stacks:/opt/ros/electric/ros]
carlos@Carlos-PC:/opt/ros/electric/ros$