Java

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Java on Fedora

Fedora uses a Free software stack that consists of OpenJDK, GNU Compiler for Java, GNU classpath and the Eclipse Java compiler to implement Java. See our JavaFAQ for more information on that. Note that AOT compilation using GCJ has been deprecated (made optional) and new packages or updated ones will be built with OpenJDK in a regular Java compilation to bytecodes.

Software mentioned on this page may come in different packaging formats. Fedora's own packages (RPM) are easy to install (with Yum) and installation instructions can be found from Docs/Drafts/SoftwareManagementGuide. Third party packages may be in archive formats (.zip, tar) and then case specific instructions should be provided.

Terminology

In Java context, terms may be a bit confusing for newcomers. JRE (Java Runtime Environment) stands for virtual machine, which is able to run Java programs.

JDK (Java Development Kit) or SDK (Software Developmenet Kit) is needed to develop Java programs. Many SDK packages these days also ship JRE, or to confuse more, no separate JRE is provided and thus terminal installations are supposed to include the development environment.

Terms AOT (Ahead of Time]), SE, J2EE need some more explanation.


Java Runtime Environments (JRE)

Java's history is well known to consist different JRE implementations and wide variety of combinations which work together. Different implementations can be installed simultaneously to Fedora and activated one at the time. Activation is done using the Alternatives system (also used to change some other subsystems). Java's subsystem name is surprisingly java and typical commands include:

# alternatives --display java
# alternatives --config java

See alternative's own documentation for more information for usage and parts involved.

Should be noted that JRE implementations installed outside Fedora distribution, may not support alternatives and thus not be visible there. Then the symbolic links under directory /etc/alternatives must be manually fixed.

OpenJDK and project IcedTea

Fedora has shipped OpenJDK as default JRE implementation since Fedora release 9. It's based on Sun Microsystem's JavaOne open source release and complemented by Red Hat's IcedTea project that implements the missing third party components that Sun could not release under free License.

OpenJDK package name on Fedora is java-1.6.0-openjdk.

GNU GCJ+GIJ for Java

The GNU Project's Java compiler and interpreter implementations provide a working JRE environment. GCJ is a Java compiler that produces bytecode for Java virtual machine GIJ.

GCJ JRE package on Fedora is java-1.5.0-gcj.


Sun Microsystems Java SE

Original Sun Microsystem's Java SE (Standard Edition) can be downloaded directly from http://www.java.com/en/download/ and installed manually.

Note x86_64 users: Based on Mozilla FAQ
Sun does not currently have a working Java plugin for x86_64 

tuju@iki.fi confirms this.

Troubleshooting JRE

Fedora's JRE in browser environment can be tested using the following test pages:


For all Java subsystem debugging, installing the symbols package java-1.6.0-openjdk-debuginfo is essential. All debuginfo sub-packages reside in own repository which needs to be enabled for installation at least. An example yum command:

# yum install --enablerepo=fedora-debuginfo -y java-1.6.0-openjdk-debuginfo


Firefox detected plugin list can be seen by typing the url:

about:plugins

Firefox can be run in debug mode as follows:

$ ICEDTEAPLUGIN_DEBUG=true firefox <URL above> 2>&1 | tee console.log

This will write the standard output also to a file.

Browser plugin also writes files under user's

~/.icedteaplugin/java.stdout   ~/.icedteaplugin/java.stderr

All these files are valuable information which can/should be attached to a bug reports.

OpenJDK does not ship the Java console anymore, but one can be found from Firefox Web Developer add-on which is installed separately to the Firefox. Add-ons are installed using Firefox's own software component management system, not Fedora's RPM.

Java Develoment Tools (SDK)

Eclipse

See our Eclipse page for an integrated development environment platform that itself is written in Java and has plugin support for many programming languages.

Maven

Fedora includes a somewhat customized version of Maven in the distribution. The customization is purely to make Maven work well in offline mode with the rest of the system. Details on how packagers can use this customized Maven are located at Java/JPPMavenReadme . We are in the process of upgrading from maven2 2.0.4 to maven2 2.0.8 (ETA = F12). Once that is achieved we will proceed immediately to maven2 2.0.9 and then to 2.0.10. The reason for going by steps is that it is easier to bootstrap a maven2 release from the previous one. Also related to maven2, a feasibility study is being performed to change the installation of Java packages to become a valid maven2 repository. We will no longer have to modify maven2 (not even with our small patch), and it wil be easier to support parallel installation of either "legacy" or "progressive" versions of Java packages. Once some positive results are obtained, it will be discussed on the fedora-devel-java-list.


Java Server Side Environments

Apache Tomcat

Fedora ships Apache Tomcat as part of standard distribution.

Apache Tomcat package name on Fedora is tomcat6.

JBoss

Teaching and Learning Java

As part of planning and implementing new 100% FLOSS Java components into Fedora, this draft document has been opened to give developers a place to teach each other about best practices, patterns, etc.

Docs/Drafts/JavaProgramming


Open Issues with Java packages

Communicate

You can subscribe to fedora-devel-java-list or talk to us in #fedora-java Freenode IRC channel. Read Communicate page for more information.

See Also

References