z2-Environment

h2. Java 9 Support (#1991)

h2. Supporting the Java 9 Language

We integrate ECJ version 4.7.2 from the download link below. Java 9 is fully supported since 4.7.1a ("New and Noteworthy 4.7.1a":https://www.eclipse.org/eclipse/news/4.7.1a/)

* "JDT Core 4.7.2":http://download.eclipse.org/eclipse/downloads/drops4/R-4.7.2-201711300510/#JDTCORE

* "New and Noteworthy 4.7.1a":https://www.eclipse.org/eclipse/news/4.7.1a/

* "JDT Core Git":https://git.eclipse.org/c/gerrit/jdt/eclipse.jdt.core.git/

* "JDT Core main":https://www.eclipse.org/jdt/core/dev.php

* "Oxygen help":http://help.eclipse.org/oxygen/index.jsp

We support a new LangLevel.JAVA9 and derive all compiler settings accordingly.

Unfortunately using Java 9 actually requires an updated Jetty version ([[Jetty9_4_support]]).

h2. Supporting the Module System

The Java 9 module system provides for module level package exports and cross-module dependencies. As such it does not contradict the class loading delegation model but rather adds that dimension to the module system as _Layers_.

The module system has migration tools, such as the unnamed module (of the classloader) and automatic modules. 

From a Z2 perspective it is almost a binary decision to either:

a) Automatically / semi-automatically modularize all Z2 modules by typically generated module-info data and declarations that support to add legacy modules are automatic modules, or

b) go for completely automatic modules by default.

As the module system adds very little value to a Z2 modularized environment and it is currently not clear how forceful other frameworks will adapt module-info data, a first release may opt for b).

References

* "State of the module system (easy and comprehensive read)":http://openjdk.java.net/projects/jigsaw/spec/sotms/

* "Project Jigsaw":http://openjdk.java.net/projects/jigsaw/

* "Jigsaw delivered":https://mreinhold.org/blog/jigsaw-complete