Wednesday Jun 08, 2011

Moving to OpenJDK as the official Java SE 7 Reference Implementation

Update 7/22/2011: The JavaSE 7 Reference Implementation is now available for download from java.net.

We are now less than two months away from the JDK 7 release date. In parallel with the development project, Oracle and the other members of the Java SE 7 Expert Group have been putting the finishing touches to the Java SE 7 specification (JSR 336). In its role as the specification lead, Oracle is responsible for delivering the Java SE 7 Reference Implementation. In line with our strategy towards a more open Java ecosystem, we are going to provide a Reference Implementation that is based entirely on the OpenJDK open source code and make it available under the GPL open source license.

The role of the Reference Implementation (RI) is to be used as the gold standard for all Java implementations. In order to have an implementation certified as Java SE compatible, an implementor must pass a large number of compatibility tests - the Technology Compatibility Kit (TCK). Furthermore, implementations may be compared to the RI as an additional check of compatibility. Basically, if your implementation has been certified to have the same behavior as the RI then it is Java compatible. For more information on this topic, consult the JCP FAQ.

Historically, Sun always used the Sun JDK as the RI and made it available under the Binary Code License (BCL). This was very convenient for Sun since it meant that its product implementation was compatible by definition. However, it was also confusing since the Sun JDK contained quite a few features that were not part of the standard, such as the Java Plugin. Also, continuing this practice would make things difficult for open source implementors as they would not be able to study and evaluate the official RI source code. (The source code for the Oracle JDK is slightly different from OpenJDK - something we will be addressing moving forward).

With that in mind, Oracle will:

  • Create RI binaries based only on the OpenJDK code base.
  • Make RI binaries available under the BCL (the normal Java license) for commercial implementors and GPLv2 (with the Classpath exception) for open-source implementors.
  • Continue to provide the TCK to commercial licensees, but also update the OCTLA license so that it covers Java SE 7. The latter allows open source implementators gratis access to the TCK to verify their implementations.

We believe that these changes will lead to improved clarity in the Java community, as well as make things easier for both commercial and open source Java SE implementors.

Update: I have been asked to make a couple of clarifications. First, there is no change to our policy vs Apache Harmony. OCTLA is a program that allows free access to the TCK for OpenJDK-derived implementations licensed under GPL and is only intended for that purpose. Second, the Oracle implementation (what you find on java.com or java.oracle.com) will remain under the BCL license only. Finally, to be completely clear, the OpenJDK source code remains under GPL.

About

Henrik Stahl is VP of Product Management in the Java Platform Group at Oracle, and is responsible for product strategy for Java ME and SE.

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