OpenJDK is a free and open source implementation of the Java Platform, Standard Edition.
It is the result of an effort Sun Microsystems began in 2006.
The implementation is licensed under the GNU General Public License with a linking exception.
Were it not for the GPL linking exception, components that linked to the Java class library
would be subject to the terms of the GPL license.
OpenJDK is the official Java SE 7 reference implementation.
Components The OpenJDK project consists of a number of
components.
Principally these are HotSpot, the Java Class Library and the javac Java compiler.
The web browser plugin and Web Start which are part of Oracle Java are not included in
OpenJDK.
Sun previously indicated that they would try to open source these components but neither
Sun nor Oracle have done so.
The only currently available free plugin and Web Start implementation are those provided
by IcedTea.
Supported JDK versions OpenJDK was initially based only on the JDK
7 version of the Java platform.
There are several separate OpenJDK projects: The OpenJDK 8 project, which is the basis
for JDK 8, was released on 18th March 2014.
The OpenJDK 7u project, which is based on JDK 7 and produces updates to the existing
Java 7 releases.
The OpenJDK 6 project, which is based on JDK 7, retrofitted to provide an open-source version
of Java 6.
IcedTea and inclusion in software distributions
In order to bundle OpenJDK in Fedora and other free GNU/Linux distributions, OpenJDK needed
to be buildable using only free software components.
Due to the encumbered components in the class library and implicit assumptions within the
build system that the JDK being used to build OpenJDK was a Sun JDK, this was not possible.
To achieve openness, Red Hat started the IcedTea project in June 2007.
It began life as an OpenJDK/GNU Classpath hybrid that could be used to bootstrap OpenJDK,
replacing the encumbrances with code from GNU Classpath.
On November 5, 2007, Red Hat signed both the Sun Contributor Agreement and the OpenJDK
Community TCK License.
One of the first benefits of this agreement is tighter alignment with the IcedTea project,
which brings together Fedora, the Linux distribution, and JBoss, the application server, technologies
in a Linux environment.
IcedTea provided free software alternatives for the few remaining proprietary sections
in the OpenJDK project.
In May 2008, the Fedora 9 and Ubuntu 8.04 distributions included IcedTea 6, based completely
on free and open source code.
Fedora 9 was the first version to be shipped with IcedTea6, based on the OpenJDK6 sources
from Sun rather than OpenJDK7.
It was also the first to use OpenJDK for the package name instead of IcedTea.
Ubuntu also first packaged IcedTea7 before later moving to IcedTea6.
Packages for IcedTea6 were also created for Debian and included in lenny.
On July 12, 2008, Debian accepted OpenJDK-6 in unstable, and it is now in stable.
OpenJDK is also available on openSUSE, Red Hat Enterprise Linux and RHEL derivatives
such as CentOS.
In June 2008, Red Hat announced that the packaged binaries for OpenJDK on Fedora 9, built using
IcedTea 6, had passed the Technology Compatibility Kit tests and could claim to be a fully compatible
Java 6 implementation.
In July 2009, an IcedTea 6 binary build for Ubuntu 9.04 passed all of the compatibility
tests in the Java SE 6 TCK.
Since August 2008, OpenJDK 7 is runnable on Mac OS X and other BSD variants.
History
Sun's promise and initial release Sun announced in JavaOne 2006 that Java would
become open-source software, and on October 25, 2006, at the Oracle OpenWorld conference,
Jonathan Schwartz said that the company intended to announce the open-sourcing of the core
Java Platform within 30 to 60 days.
Sun released the Java HotSpot virtual machine and compiler as free software under the GNU
General Public License on November 13, 2006, with a promise that the rest of the JDK would
be placed under the GPL by March 2007, "except for a few components that Sun does not have
the right to publish in source form under the GPL".
According to free-software advocate Richard Stallman, this would end the "Java trap",
the vendor lock-in that he argues applied to Java and programs written in Java.
Release of the class library Following their promise to release a Java
Development Kit based almost completely on free and open source code in the first half
of 2007, Sun released the complete source code of the Java Class Library under the GPL
on May 8, 2007, except for some limited parts that had been licensed to Sun by third parties
and Sun was unable to re-license under the GPL.
Included in the list of encumbered parts were several major components of the Java graphical
user interface.
Sun stated that it planned to replace the remaining proprietary components with alternative
implementations and to make the class library completely free.
When initially released in May 2007, 4% of the OpenJDK class library remained proprietary.
By the appearance of OpenJDK 6 in May 2008, less than 1% remained, making it possible
to build OpenJDK without any binary plugs.
The binary plug requirement was later dropped from OpenJDK 7 as part of b53 in April 2009.
This was made possible, over the course of the first year, by the work of Sun Microsystems
and the OpenJDK community.
Each encumbrance was either released as free and open source software or replaced with
an alternative.
Beginning in December 2010, all the so-called binary plugs were replaced by Open source
replacements, making the whole JDK open sourced and the binary plugs not necessary anymore.
Community improvements On November 5, 2007, Red Hat announced an
agreement with Sun, signing Sun's broad contributor agreement and Sun's OpenJDK Community Technology
Compatibility Kit License Agreement.
Also on November 2007, the Porters Group was created on OpenJDK to aid in efforts to port
OpenJDK to different processor architectures and operating systems.
The BSD porting project is led by Kurt Miller and Greg Lewis and the Mac OS X porting project
led by Landon Fuller have expressed interest in joining OpenJDK via the Porters Group and
as of January 2008 are part of the mailing list discussions.
Another project pending formalization on the Porters Group is the Haiku Java Team, led
by Bryan Varner.
On December 2007, Sun moved the revision control of OpenJDK from TeamWare to Mercurial, as
part of the process of releasing it to open source communities.
OpenJDK has comparatively strict procedures of accepting code contributions: every proposed
contribution must be reviewed by another OpenJDK committer and the contributor must have signed
the Sun/Oracle Contributor Agreement.(SCA/OCA) Preferably, there should also be a jtreg test
demonstrating that the bug has been fixed.
Initially, the external patch submission process was slow and commits to the codebase were
only made by Sun engineers, until September 2008.
The process has improved and, as of 2010, simple patches and backports from OpenJDK
7 to OpenJDK 6 can take place within hours rather than days.
Collaboration with IBM, Apple, and SAP On October 11, 2010, IBM, by far the biggest
participant in the Apache Harmony project, decided to join Oracle on the OpenJDK project,
effectively shifting its efforts from Harmony to OpenJDK.
Bob Sutor, IBM's head of Linux and open source, blogged that "IBM will be shifting its development
effort from the Apache Project Harmony to OpenJDK".
On November 12, 2010, Apple Inc. and Oracle Corporation announced the OpenJDK project
for Mac OS X.
Apple will contribute most of the key components, tools and technology required for a Java SE
7 implementation on Mac OS X, including a 32-bit and 64-bit HotSpot-based Java virtual
machine, class libraries, a networking stack and the foundation for a new graphical client.
On January 11, 2011, the Mac OS X Port Project was created on OpenJDK, and Apple made the
first public contribution of code to the project.
The initial Apple contribution built on the OpenJDK BSD port.
In July 2011, SAP AG announced that SAP officially joined the OpenJDK project.
See also
javac, Oracle Corporation's Java compiler, now under a GPL license
HotSpot, Oracle Corporation's Java virtual machine, now under a GPL license
Java Class Library Free Java implementations
Java Platform, Standard Edition Apache Harmony
IcedTea References
External links Main site
OpenJDK – The First Year by Mark Reinhold Zero and Shark: a Zero-Assembly Port of OpenJDK