From the Developer day of the Hungarian Oracle User Group. 2015.10.08 Author: Marton Elek, DPC Consulting Event: HOUG Szakmai nap 2015, 2015.10.07

1. Java SE 9, Project Jigsaw
Elek Márton
@anzix
2015 March
DPC Consulting

2. Java 9 roadmap
2015/09/08 Mark Reinhold: The state of the
module system (Java 9 b83)
2015/12/10 Feature Complete
2016/02/04 All Tests Run
2016/02/25 Rampdown Start
2016/04/21 Zero Bug Bounce
2016/06/16 Rampdown Phase 2
2016/07/21 Final Release Candidate
2016/09/22 General Availability

3. Planned features

4. Improvements
● Java REPL
● HTTP2 Client
● UTF-8 Property files
● Microbenchmark Suite
● Compiler improvements
● Money and Currency API, JSR-354 (?)
● JSON API (? - proposed to be dropped)
● ProcessAPI update (pid, process list)
● HTML5 Javadoc
● Make G1 the default GC algorithm
● Remove deprecated GC combinations

5. Modularization

6. Related JEPs/JSR
JEP 200: The Modular JDK
JEP 201: Modular Source Code
JEP 220: Modular Run-Time Images
JEP 162: Prepare for Modularization (Java8)
JSR 376: Java Platform Module System
Good source:
Mark Reinhold: The state of the module system

7. Getting started
Create your first module:
● traditional JAR file with
● module-info.java
module hu.dpc.java9.logger {
}

8. Compile the module
● Could be compiled with standard tools (maven) if
there are no dependencies
● Command line tools are also changed
javac
-d /tmp/modules/hu.dpc.java9.logger
-modulepath /tmp/modules
-sourcepath src/main/java …..java

9. Using the logger
Create your first module:
● traditional JAR file with
● module-info.java
module hu.dpc.java9.logger {
exports hu.dpc.java9.logger;
}

10. Using logger
public class App {
public static void main(String[] args)
LoggerFactory.getLogger().log("Hello world");
}
}
module hu.dpc.java9.app {
requires hu.dpc.java9.logger;
}

11. Package level dependencies
Source: M Reinhold: The state of the
module system

12. Why we need classloaders?
● Classloader is for creating new classes
● Reference to a class could be used even without
explicit export
LoggerImpl
App
LoggerFactory
Logger
exports
requires

13. Compile and run
javac
-d /tmp/modules/hu.dpc.java9.logger
-modulepath /tmp/modules
-sourcepath src/main/java ....java
java
-mp /tmp/modules
-m hu.dpc.java9.app/hu.dpc.java9.App

14. Backward compatibility
java
-mp /tmp/modules
-m hu.dpc.java9.app/hu.dpc.java9.App
java
-cp /tmp/modules/hu.dpc.java9.app:/tmp/modules/hu.dpc.java9.logger
hu.dpc.java9.App

15. Packaging: jmod
● Accommodate native code, configuration files, and
other kinds of data
● "Whether this new format, provisionally named
“JMOD,” should be standardized is an open
question."

16. JDK modules
● Most of the APIs
are modularized
● can’t be used
without proper
requires in
module-info

17. Service layer

18. Service Layer
logger-framework.jar
logger-mysql.jar
interface Logger{...}
class MysqlLogger{...}
class LoggerFactory{...

19. Service Layer
logger-framework.jar
logger-syslog.jar
interface Logger{...}
class SyslogLogger{...}
class LoggerFactory{...

20. Service Layer - Java 6-8
Service Provider Interface
● Which are the implementation of a specific
interface?
ServiceLoader<Logger> loggers =
ServiceLoader.load(Logger.class);
for (Logger logger: loggers) {
logger.log("hello world");
}
}

21. Service Layer - Java 6-8
ServiceLoader<Logger> loggers =
ServiceLoader.load(Logger.class);
for (Logger logger: loggers) {
logger.log("hello world");
}
}
Definition (in the jar file):
META-INF/services/hu.dpc.java9.logger.Logger
hu.dpc.java9.logger.internal.LoggerImpl

22. Service Layer - Java 6-8
logger-framework.jar
logger-mysql.jar
interface Logger{...}
class MysqlLogger{...}
class LoggerFactory{...

23. Service Layer - Java 9
Usage:
ServiceLoader<Logger> loggers =
ServiceLoader.load(Logger.class);
for (Logger logger: loggers) {
logger.log("hello world");
}
}

24. Definition
In the hu.dpc.java9.logger module:
module hu.dpc.java9.logger {
exports hu.dpc.java9.logger;
provides hu.dpc.java9.logger.Logger
with hu.dpc.java9.logger.internal.LoggerImpl;
}
In the hu.dpc.java9.app module
module hu.dpc.java9.app {
requires hu.dpc.java9.logger;
use hu.dpc.java9.logger.Logger;
}

25. Non requirements
● Modularize the Java Language Specification
● Modularize the Java Virtual Machine Specification
● Multiple versions
● Version selection
● Strict classloader requirements
See: http://openjdk.java.net/projects/jigsaw/spec/reqs/

26. Java 9 vs OSGi
Java 9 / Jigsaw OSGi
metadata module-info.java (nincs meta adat) META-INF
classpath
separation
exports/requires Import-Package/Export-Package
classpath++ transitive imports, fragment bundle/dynamic import
classloader
hierarchy
ClassLoader: unspecified strict, per bundle
service layer static (get implementations) dynamic (get implemetations +
start/stop listeners)
services interface + implementation for the standard
services (logging, config...)
versioning no yes

27. Summary/Future
● Summary
– classpath separation: private/public
– service locator (based on existing SPI)
– modularized JVM APIs
● Not scope
– versioning!
– strict class loader rules
● Shoud be upgraded:
– all the IDEs
– all the build tools (maven, gradle)
– all the JVM based languages (Scala, Clojure)
● SPI
– could be more widely adopted