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.

c) Ignore the Java 9 module layer and stay with unnamed modules and the existing class loader separation

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 c)

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