Documentation Java Beat

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Java

Best of breed free software Java implementation

Fedora includes multiple best of breed free software Java(TM) implementations, obtained through active adoption of innovative technology integrations produced by Fedora and others within upstream projects. The implementations integrated into Fedora are based on OpenJDK (http://openjdk.java.net/) and the IcedTea GNU/Linux distribution integration project (http://icedtea.classpath.org/), or based on alternatives such as the GNU Compiler for Java (GCJ - http://gcc.gnu.org/java) and the GNU Classpath core class libraries (http://www.gnu.org/software/classpath/). All Fedora innovations are pushed upstream to get the widest possible integration of the technologies in general Java implementations.

The implementation of OpenJDK 6 included in Fedora 10 uses the HotSpot virtual machine runtime compiler on x86, x86_64, and SPARC. On PowerPC (PPC) it uses the zero interpreter, which is slower. On all architectures an alternative implementation based on GCJ and GNU Classpath is included that includes an ahead-of-time compiler to produce native binaries.

Fedora binaries for selected architectures (currently only x86 and x86_64 based on OpenJDK) are tested against the Java Compatibility Kit (JCK) by Red Hat to guarantee 100% compatibility with the Java Specification (JDK 1.6 at this time).

Handling Java Applets and Web Start Applications

In Fedora 10 gcjwebplugin has been replaced by IcedTeaPlugin, which runs untrusted applets safely in a Web browser and works on any architecture. You can see which Applet Plugin is installed by typing about:plugins in Firefox. The new plugin adds support for the JavaScript bridge (LiveConnect) that was missing from earlier versions. For more details on the bytecode-to-JavaScript bridge (LiveConnect), refer to the bug report:

https://bugzilla.redhat.com/show_bug.cgi?id=304021

Feedback on the security policy is appreciated. If you suspect the security policy may be too restrictive to enable restricted applets, follow this procedure:

  1. Run the firefox -g command in a terminal window to see what is being restricted.
  2. Then grant the restricted permission in the /usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0/jre/lib/security/java.policy file.
  3. File a bug report, so your exception can be included in the packaged security policy. Packaging these exceptions allows system owners to avoid having to hack the policy file in the future.

Experimental Web Start (javaws) support via NetX has been added to the IcedTea repository. When a Java Network Launching Protocol (.jnlp) file is embedded on a web page you can open it with the IcedTea Web Start (/usr/bin/javaws). For more information on NetX, refer to:

http://jnlp.sourceforge.net/

New integration with other Fedora technologies

Through the IcedTea project OpenJDK has been integrated with several new technologies that are also part of Fedora 10.

VisualVM integration through the NetBeans framework

VisualVM (jvisualvm) provides a graphical overview of any local or remotely running Java application, letting you monitor all running threads, classes, and objects allocated by the application by taking thread dumps, heap dumps, and other lightweight profiling tools.

PulseAudio integration for javax.sound

PulseAudio integrations provides all the benefits of PulseAudio to any java application using the javax.sound package.

Integration of Mozilla Rhino (JavaScript)

Rhino is a pure-Java JavaScript implementation from Mozilla providing an easy mixing of Java and JavaScript for developers using the javax.script package.

Other improvements

Also in Fedora 10 Java cryptography (javax.crypto) is fully supported without any (regional) restrictions.

Fedora and JPackage

Fedora 10 includes many packages derived from the JPackage Project.

http://jpackage.org

Some of these packages are modified in Fedora to remove proprietary software dependencies, and to make use of GCJ's ahead-of-time compilation feature. Use the Fedora repositories to update these packages, or use the JPackage repository for packages not provided by Fedora. Refer to the JPackage website for more information about the project and the software it provides.

Admonition("warning", "Mixing Packages from Fedora and JPackage", "Research package compatibility before you install software from both the Fedora and JPackage repositories on the same system. Incompatible packages may cause complex issues.")

Note on upgrading from Fedora 8 - OpenJDK Replaces IcedTea

Since Fedora 9 the packages called java-1.7.0-icedtea* in Fedora 8 have been renamed to java-1.6.0-openjdk*. The Fedora 8 IcedTea packages tracked the unstable OpenJDK 7 branch, whereas the java-1.6.0-openjdk* packages track the stable OpenJDK 6 branch. All the upstream IcedTea sources are included in the java-1.6.0-openjdk SRPM.

If you are upgrading from a system based on Fedora 8 that still has IcedTea installed, the package changeover does not happen automatically. The packages related to IcedTea based on OpenJDK 7 must first be erased, then the new OpenJDK 6 packages installed.

su -c 'yum erase java-1.7.0-icedtea{,-plugin}'
su -c 'yum install java-1.6.0-openjdk{,-plugin}'

Upgrading from Fedora 9 does not require special action.