Uploaded image for project: 'JDK'
  1. JDK
  2. JDK-6606784

Add support for launching applets from JNLP files



    • Subcomponent:
    • Resolved In Build:
    • CPU:
      generic, x86
    • OS:
      generic, windows, windows_nt, windows_xp
    • Verification:



        The new out-of-process Java Plug-In is capable of spawning a new JVM
        instance to run a particular applet. With this capability, it is now
        feasible to launch applets directly from JNLP files, which can contain
        elements describing a JRE version, JVM command-line arguments, heap
        size and the like.

        This capability would be a major improvement for developers. Existing
        and future JNLP extensions for 3D, spatialized audio, video, etc.
        would immediately work transparently for both applets and Java Web
        Start applications.

        The following describes the approximate launch sequence in the context
        of the new Java Plug-In.

        1. A plugin instance is created for an applet tag looking something
           <applet href="http://.../foo.jnlp">

        2. A StartAppletMessage is passed to an attached client JVM process,
        exactly as is currently done. Note that if a JVM instance must be
        created for this purposes, the default command-line arguments are

        3. The client JVM must recognize that the incoming parameters of the
        StartAppletMessage represent a launch from a JNLP file rather than a
        launch from a traditionally-formed applet tag -- the presence of the
        "href" parameter is probably the best indication, in which case the
        code base, archive tag, etc. (if present) would be ignored.

        4. The client JVM makes the network connections to download the main
        JNLP and parses it, downloading and parsing any extension JNLPs as
        well. Ideally code from Java Web Start can be used unmodified for this

        5. The client JVM determines based on the JRE version, command-line
        arguments, etc. used to launch the current JVM whether the currently
        executing JVM is capable of satisfying the parameters required by the

        6. If the currently running JVM instance can not satisfy the
        parameters requested in the JNLP file, a relaunch is needed. In this
        case, the client JVM sends a message back to the web browser
        containing all of the results of parsing all of the JNLPs, so that
        re-downloading and re-parsing is not necessary. The associated data
        structures for this purpose might be more complex than the basic
        Serializer class currently supports (two-dimensional arrays of Strings
        are about the most complex structure for which it has built-in
        support). We would need to consider adding either more support to the
        Serializer (for example, three-dimensional arrays of Strings) or
        writing helper classes for serialization of this information.

        7. Once we are in the JVM instance in which the launch will occur,
        checks are needed to see whether all of the system properties, for
        example, requested in the JNLP file are "secure" system properties. A
        check to see whether the target applet is signed may be required at
        this point. (Other policies enforced by Java Web Start in this area,
        such as a maximum heap size, should be enforced as well.)

        8. If all checks pass, the launch of the applet proceeds in this JVM.

        Some issues:

         - javaws.jar will need to be placed on the boot class path along with
           deploy.jar and plugin.jar in JavaVM.c. We need to think about
           whether we want to guarantee the availability of things like the
           Java Web Start services (in particular, the PersistenceService) for
           all applets or just ones launched via JNLP files. We might need to
           play tricks with permissions and accessClassInPackage if we decide
           to only support this for JNLP-launched applets.

         - Some changes are known to be needed to the Applet2ClassLoader
           implementation in order to be compatible with support for Java Web
           Start. For example, the JNLPClassLoader overrides
           ClassLoader.findLibrary() in order to provide support for nativelib
           jar files. Currently the Applet2ClassLoader does not override
           findLibrary() at all.

           An issue in this area is that the Applet2ClassLoader is tightly
           bound to the Applet2SecurityManager, so we can't simply switch away
           from using the Applet2ClassLoader. Ideally we could refactor the
           bulk of the code in the JNLPClassLoader into a helper class (which
           wouldn't actually be a ClassLoader) so that the JNLPClassLoader
           would then become a thin skeleton and the Applet2ClassLoader could
           then refer to that code. Other solutions might be possible.
        As part of this feature it would be nice if we could support changing the icon in security dialogs when a validated certificate is in use. This was requested on the JavaDesktop forums at http://forums.java.net/jive/thread.jspa?threadID=31538&tstart=0 . See comments for more details.
        Support for the nativelib tag in extension JNLPs needs to be done slightly differently than in Java Web Start. In the Java Plug-In, it is feasible that more than one class loader in the same JVM instance may attempt to reference the same JNLP extension containing native code, and ultimately try to load the same DLL / .so off the local disk. Loading the same shared object in multiple class loaders is forbidden due to type safety issues (see section 11.2.4 in the book "The Java Native Interface").

        The solution to this problem in the Java Plug-In's class loader supporting JNLP will be to make a fresh copy of the native library into a temporary directory before loading it in a given ClassLoader instance. Note that at most one copy needs to be made for a given ClassLoader. This is what is done in the JNLPAppletLauncher at http://applet-launcher.dev.java.net/ .


            Issue Links



                sgothelsunw Sven Gothel (Inactive)
                kbr Kenneth Russell (Inactive)
                0 Vote for this issue
                0 Start watching this issue