Java 9 Deep Dive at EclipseCon 2015

The Java community is still rolling around in the awesomeness of the long-awaited Java 8 release, with its support for lambda expressions, virtual extension methods and streams, compact profiles, the new the date/time API and so much more (but mostly that stuff). It was the largest-ever upgrade to the programming model, and by some accounts, it has been the most rapidly adopted update in the history of the platform.

But, you ask, what about Java 9?

Mark Reinhold, chief architect of Oracle's Java Platform Group, offered attendees at EclipseCon 2015, which wrapped on Thursday, a deep dive into the Even Cooler Java update, coming sometime next year.

The big change in Java 9, as everyone knows, is modularity, as laid out in Project Jigsaw, the oft-deferred capability that aims to make it possible for Java developers to create apps that don't need to lug around the entire environment. A Jigsaw module is a collection of Java classes, native libraries and other resources, along with metadata.

"From the beginning, the Java SE platform has been this huge monolithic thing," Reinhold said. "Even if you wanted to use just a small part of it, you had to install all of it." It has been difficult to run Java SE on small devices, he observed, but it has also been a pain on large devices and in some cloud environments. "What we want is a box of Lego parts [which are] modular that we can assemble as needed," he said.

The introduction of compact profiles in Java 8 was a "baby step" toward relieving some of that pain, Reinhold said, but Java 9 "will be composed of a set of finer-grained modules and will include tools to enable developers to identify and isolate only those modules needed for their application," he said.

Project Jigsaw comprises the three JEPs and a JSR. JEPs (JDK Enhancements Proposals) allow Oracle to develop small, targeted features for the Java language and virtual machine outside the Java Community Process (JCP), which requires full Java Specification Requests (JSRs).

• JEP 200: The Modular JDK, defines a modular structure for the JDK. Reinhold described it as an "umbrella for all the rest of them."
• JEP 201: Modular Source Code reorganizes the JDK source code into modules.
• JEP 220: Modular Run-Time Images restructures the JDK and JRE run-time images to accommodate modules.
• JSR 376: Java Platform Module System, the central component of Project Jigsaw, which defines the module system for the Java Platform.

Among other things, the modularization of Java will lead to the removal of the rt.jar files (runtime JAR), which Reinhold referred to as "a constant source of pain," in favor of compact profiles for a major reduction of the JVM footprint. (JAR files, he added, would be with us "until the heat death of the universe.") While the full JRE clocks in at 55Mb on a Linux ARM 32, Reinhold noted, compact1, the smallest profile, clocks in at 11Mb; compact2 is 17Mb, and compact3 is 30Mb. The modularization project will also lead to the elimination of the extension classpath and some reorganization of the lib path, he said.

Modularity will also improve security, he said. After "a bit of a rough period," Java security is now much better, but Java 9 will make it even better by making it possible to enforce strong modular boundaries -- defining what's internal to the module and what's external. Java 9 will also introduce a tool called jlink or the Java linker, which will make it possible to link modules to a single runtime.

"Vanilla Java is a dynamically linked environment," Reinhold said. "But when you are assembling modules into a one pile of bits that is custom JRE, you need a linker."

Of course, there's already a modular architecture for Java. The OSGi Alliance currently provides set of specifications that define a dynamic component system for the platform. Reinhold responded to the inevitable question about whether Java 9's new modular system will be compatible OSGi's modular architecture.

"We intend to explore ways of making standard Java modules available to other module systems," he said, but added, "We don't see how to achieve all of the goals we have for the module system if one of those goals is also to be completely compatible with OSGi."

Reinhold also looked into his crystal ball and speculated a bit on developments beyond Java 9. He touched on current efforts to improve Java's typing system and make the language more efficient at handling situations requiring identity less types via Project Valhalla , announced in August. He also pointed to Project Panama, which aims to improve the connections between the JVM and "foreign" non-Java APIs.

Posted by John K. Waters on March 13, 2015