The document provides an overview of new features in Java 9, including the Java Platform Module System, JShell REPL, Reactive Streams, Process API, and HTTP Client API. The Java Platform Module System introduces modules that provide reliable configuration and strong encapsulation. JShell allows evaluating code interactively. Reactive Streams support asynchronous stream processing. The Process API provides a new way to manage operating system processes. And the HTTP Client API improves HTTP client functionality.

1. Java 9 Overview

2. Mateusz
Skawiński
I work on position of Technical Leader in SoftServe. I work with Java on
professional, commercial projects since 2009. Over the years, I was interested and
involved in using object oriented programming in large enterprise applications.
Currently working on real time data integrations of large HCM systems.

3. Agenda
• Java Platform Module System
• JShell
• Reactive Streams
• Process API
• HTTP API
• Other

4. Java Platform
Module System

5. Java Platform Module System – What?
• JSR 376 – Project Jigsaw (http://openjdk.java.net/projects/jigsaw)
• Named, self-describing collection of code and data.
• JDK has been divided into a set of modules.
• Adds a higher level of aggregation above packages.

6. Java Platform Module System – Why?
• Reliable configuration, to replace classpath mechanism with a means for program components
to declare explicit dependences upon one another.
• Strong encapsulation, to allow a component to declare which of its public types are accessible to
other components, and which are not.
• Make it easier for developers to construct and maintain libraries and large applications.
• Improve the security and maintainability of Java SE Platform Implementations in general, and the JDK
in particular.
• Enable improved application performance.
• Enable the Java SE Platform, and the JDK, to scale down for use in small computing devices and
dense cloud deployments.

7. Java Platform Module System – How?
• Define a module: Files structure module-info.java
• Declare requirements
• Define exposed packages
module com.itc {
requires com.coffee;
requires com.tea;
exports com.itc;
}

8. Example – com.coffee

9. Example – com.coffee
package com.coffee;
public interface Coffee {
void drink();
}
package com.coffee;
import com.coffee.types.Arabica;
import com.coffee.types.Robusta;
public class CoffeeMaker {
public Coffee brewArabica() {
return new Arabica();
}
public Coffee brewRobusta() {
return new Robusta();
}
}
module com.coffee {
exports com.coffee;
}

10. Example – com.coffee.types
package com.coffee.types;
import com.coffee.Coffee;
public class Arabica implements
Coffee {
@Override
public void drink() {
System.out.println
("Strong black arabica");
}
}
package com.coffee.types;
import com.coffee.Coffee;
public class Robusta implements
Coffee {
@Override
public void drink() {
System.out.println
("Full of caffeine robusta");
}
}

11. Example – com.itc
package com.itc;
import com.coffee.Coffee;
import com.coffee.CoffeeMaker;
public class ILikeCoffee {
public static void main(String[] args) {
CoffeeMaker coffeeMaker = new CoffeeMaker();
final Coffee wakeUpCoffee = coffeeMaker.brewRobusta();
final Coffee eveningCoffee = coffeeMaker.brewArabica();
wakeUpCoffee.drink(); // Full of caffeine robusta
eveningCoffee.drink(); // Strong black arabica
} …

12. Example – com.itc
package com.itc;
import com.coffee.Coffee;
import com.coffee.CoffeeMaker;
import com.coffee.types.Arabica;
public class ILikeCoffee {…
The type com.coffee.types.Arabica is not
accessible
module com.itc {
requires com.coffee;
requires com.coffee.types;
}
com.coffee.types cannot be resolved to a module

13. Backward Compatibility
• JDK was divided into set of modules – java.base – 78 modules
• Classpath can be used
• Unnamed modules
• Automatic modules

14. Unnamed Modules
• A class which is not a member of any named module.
• Classed compiled in Java 8 and older versions which are not migrated to modules when run in Java 9.
• The unnamed module requires all other available named modules.
• The unnamed module exports all its packages.
• Named modules can not have a dependency on the unnamed module.

15. Automatic Modules
• JAR files are automatically detected as modules.
• Module name will be automaticaly created based on JAR file name.
• The automatic module requires all other available named modules.
• The automatic module exports all its packages.

16. Example – com.tea
module com.itc {
requires com.coffee;
requires com.tea;
}
package com.itc;
import com.tea.Tea;
import com.tea.types.Roiboos;
public class ILikeTea {
public static void main(String[] args) {
final Tea tea = new Roiboos();
tea.drink(); } }

17. JLink
• Command line tool.
• Generate your own JRE.
• Set required modules.
• Less consumption (deployment size, memory, performance).
• Embedded, IoT, microservices.
• All in One

18. Beyond Modules

19. JShell
• Read-Evaluate-Print Loop (REPL), which evaluates declarations, statements, and expressions
as they are entered and immediately shows the results.
• Command line tool.
• Its quick, small and easy.

20. JShell – External Editor

21. Reactive Streams
• Near real time, asynchronous processing.
• Not predetermined data volume.
• Load leverage (backpressure).
• Publisher - subscriber.
• http://www.reactive-streams.org
• Multiple implementations available
Producer Subscriber
Subscription
subscribe()
create
onSubscribe(s)
alternative
[via subscription]
[direct]
send m items
request(n)
onNext() - m items
send n items
request(m)
onNext() - m items
request(n)
m >= n

22. java.util.concurrent.Flow
Modifier and Type Class Description
static interface Flow.Processor<T,R> A component that acts as both a Subscriber and Publisher.
static interface Flow.Publisher<T> A producer of items (and related control messages) received by Subscribers.
static interface Flow.Subscriber<T> A receiver of messages.
static interface Flow.Subscription Message control linking a Flow.Publisher and Flow.Subscriber.

23. java.util.concurrent.Flow
public interface Publisher<T> {
public void subscribe(Subscriber<? super T> s); }
public interface Subscriber<T> {
public void onSubscribe(Subscription s);
public void onNext(T t);
public void onError(Throwable t);
public void onComplete(); }
public interface Subscription {
public void request(long n);
public void cancel(); }
public interface Processor<T, R> extends Subscriber<T>, Publisher<R> {}

24. Process API
• Start, retrieve information about, and manage native operating system processes.
• New interfaces: ProcessHandle and ProcessHandle.Info
• Operating system independant API
• process.toHandle()
• Process class extension.

25. ProcessHandle (selected)
Modifier and Type Method Description
static Stream<ProcessHandle> allProcesses​() Returns a snapshot of all processes visible to the current process.
Stream<ProcessHandle> children​() Returns a snapshot of the current direct children of the process.
static ProcessHandle current​() Returns a ProcessHandle for the current process.
Stream<ProcessHandle> descendants​() Returns a snapshot of the descendants of the process.
ProcessHandle.Info info​() Returns a snapshot of information about the process.
CompletableFuture<ProcessHandle> onExit​() Returns a CompletableFuture<ProcessHandle> for the termination of the
process.
Optional<ProcessHandle> parent​() Returns an Optional<ProcessHandle> for the parent process.
long pid​() Returns the native process ID of the process.

26. ProcessHandle.Info
Modifier and Type Method Description
Optional<String[]> arguments​() Returns an array of Strings of the arguments of the process.
Optional<String> command​() Returns the executable pathname of the process.
Optional<String> commandLine​() Returns the command line of the process.
Optional<Instant> startInstant​() Returns the start time of the process.
Optional<Duration> totalCpuDuration​() Returns the total cputime accumulated of the process.
Optional<String> user​() Return the user of the process.

27. HTTP API
• Working with HttpURLConnection is inconvinient.
• Streams operations.
• Pre Java 9 external libs were used.
• HttpClient class.
• Supports HTTP2 spec.

28. Other
• List.of
List<String> coffies = List.of("Espresso", "Americano", "Cappuchino", "Latte");
• New default garbage collector: ParallelGC → G1GC.
• Private methods in interfaces.
• Try with resources improvement.
• Javadocs improvement (html5).
• Security improvements (incl. SHA-3 Hash algorithms)
• … and more → https://docs.oracle.com/javase/9/whatsnew/toc.htm

29. Thank you

30. See you on our next
meeting in April!
19 / 04 / 2018