Interface Daemon

  • All Known Implementing Classes:
    DaemonWrapper

    public interface Daemon
    Provides support for native daemon invocation. Using a platform dependant helper program, classes that implement the Daemon interface can be initialized, started and stopped according to the conventions of the underlying operating system.

    Implementors of this interface must also provide a public constructor with no arguments so that instances can be created in an automated fashion.

    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      void destroy()
      Frees any resources allocated by this daemon such as file descriptors or sockets.
      void init​(DaemonContext context)
      Initializes this Daemon instance.
      void start()
      Starts the operation of this Daemon instance.
      void stop()
      Stops the operation of this Daemon instance.
    • Method Detail

      • init

        void init​(DaemonContext context)
           throws DaemonInitException,
                  Exception
        Initializes this Daemon instance.

        This method gets called once the JVM process is created and the Daemon instance is created thru its empty public constructor.

        Under certain operating systems (typically Unix based operating systems) and if the native invocation framework is configured to do so, this method might be called with super-user privileges.

        For example, it might be wise to create ServerSocket instances within the scope of this method, and perform all operations requiring super-user privileges in the underlying operating system.

        Apart from set up and allocation of native resources, this method must not start the actual operation of the Daemon (such as starting threads calling the ServerSocket.accept() method) as this would impose some serious security hazards. The start of operation must be performed in the start() method.

        Parameters:
        context - A DaemonContext object used to communicate with the container.
        Throws:
        DaemonInitException - An exception that prevented initialization where you want to display a nice message to the user, rather than a stack trace.
        Exception - Any exception preventing a successful initialization.
      • start

        void start()
            throws Exception
        Starts the operation of this Daemon instance. This method is to be invoked by the environment after the init() method has been successfully invoked and possibly the security level of the JVM has been dropped. Implementors of this method are free to start any number of threads, but need to return control after having done that to enable invocation of the stop()-method.
        Throws:
        Exception - If the start was not successful
      • stop

        void stop()
           throws Exception
        Stops the operation of this Daemon instance. Note that the proper place to free any allocated resources such as sockets or file descriptors is in the destroy method, as the container may restart the Daemon by calling start() after stop().
        Throws:
        Exception - If the stop was not successful
      • destroy

        void destroy()
        Frees any resources allocated by this daemon such as file descriptors or sockets. This method gets called by the container after stop() has been called, before the JVM exits. The Daemon can not be restarted after this method has been called without a new call to the init() method.