Java 9 introduced several new features including a module system, jshell REPL environment, jlink tool for linking modules, G1 garbage collector as default, reactive streams API, improved process handling API, HTTP/2 client support, and other language and API improvements. The module system aims to address issues with the monolithic JDK by encapsulating and restricting internal APIs within named modules. Jshell brings an interactive shell to Java for testing code snippets. Jlink allows building runtime images with only required modules.

1. JAVA 9
ALİCAN AKKUS

2. JAVA 9
TIMELINE
1.0
1996
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
1997 1998 2000 2002 2004 2006 2011 2014
1.9
2017
‣ * MODULES
* JSHELL / JLINK
* G1GC
* REACTIVE API
‣ * PROCESS API
‣ * HTTP 2 CLIENT
* OTHERS..

3. JAVA 9
MODULE SYSTEM
▸ Problems;
(1) : JDK is too big.
* 4240 classes in Java 8
* 4024 classes in Java 7
* 3793 classes in Java 6
(2) : As User can access Internal APIs too, Security is also big issue.
(3) : Its a bit tough to support Less Coupling between components.
▸ Solutions;
Each Module contains only a set of related code and data to support Single Responsibility (Functionality) Principle (SRP).
1. The Moduler JDK
* Java 9 Module System has 73 modules in JDK
2. Modular Source Code
3. Encapsulate Most Internal APIs
4. Java Platform Module System(JPMS)
5. jlink: The Java Linker

4. JAVA 9 - MODULE SYSTEM

5. JAVA 9 - MODULE SYSTEM
module com.caysever.java9 {
requires java.logging;
requires jdk.incubator.httpclient;
exports com.caysever.java9.http2client;
}
Module module = moduleInfo.getClass().getModule();
Optional.ofNullable(module).ifPresent(m -> System.out.println(module.getName()));
Optional.ofNullable(module.getDescriptor().requires()).ifPresent(requires ->
Stream.ofNullable(requires).forEach(rs -> rs.forEach(r ->
System.out.println(r.name()))));
com.caysever.java9
java.logging
java.base
jdk.incubator.httpclient

6. JAVA 9 - JSHELL
▸ JShell introduces a REPL (Read-Eval-Print-Loop) environment in Java.
▸ JShell gives you a prompt (and interactive session history) so that you can type and execute Java
commands.
▸ JShell makes it really easy to write, execute and test fragments of code. So you can perform quick tasks,
test and mockup code.

7. JAVA 9 - JLINK
▸ Jlink is Java’s new command line tool which allows you to link sets of modules (and their transitive
dependencies) to create a run-time image.
▸ jlink --module-path <modulepath> --add-modules <modules> --limit-modules <modules> --output
<path>
▸ This command creates a run-time image which only has the modules that our application needs.

8. JAVA 9 - GARBAGE COLLECTOR
▸ With Java 9, the default garbage collector (GC) is being changed from the ParallelGC to the G1GC.
▸ The “Garbage-first” garbage collector, aka G1, is a concurrent multi-threaded GC. It mostly works
alongside the application threads (much like the concurrent mark sweep GC) and is designed to offer
shorter, more predictable pause times – while still achieving high throughput.
▸ G1 also tracks various metrics for each region, and calculates how long it will take to collect them – give it
a target for pause times, and it will attempt to collect as much garbage as it can within the given
constraints.
▸ You can test the G1GC yourself using the VM flag –XX:+UseG1GC.

9. JAVA 9 - REACTIVE STREAM
▸ Publisher
* Produces items for subscribers to consume. The only method is subscribe(Subscriber) whose purpose
should be obvious.
▸ Subscriber
* Subscribes to publisher(usually only one) to receive items (via method onNext(T)),
error messages (onError(Throwable)),
or a signal that no more items are to be expected (onComplete()).
Before any of those things happen, though, the publisher calls onSubscribe(Subscription)
▸ Subscription
* The connection between a single publisher and a single subscriber. The subscriber will use it to request
more items (request(long)) or to sever the connection (cancel()).

10. JAVA 9 - PROCESS API
▸ Java SE 9 is coming with some improvements in Process API. They have added couple new classes and
methods to ease the controlling and managing of OS processes.
▸ Sample;
* ProcessHandle.current().pid();
* ProcessHandle.allProcesses()
.map(p -> p.info().command())
.filter(Optional::isPresent)
.collect(Collectors.toList())
.forEach(System.out::println);
* new ProcessBuilder().command("sleep", "3").start().onExit().thenAccept(System.out::println);
* ProcessBuilder.startPipeline(List.of(new ProcessBuilder(“ls”), new ProcessBuilder(“sort”,”-u”) ));

11. JAVA 9 - HTTP 2.0
▸ Still in incubation
▸ Provides support for HTTP 2.0
▸ Sync & Async request
▸ HttpClient, HttpRequest, HttpResponse
HttpClient httpClient = HttpClient.newHttpClient();
HttpRequest httpRequest = HttpRequest.newBuilder().uri(“alicanakkus.github.io”).GET().build();
HttpResponse<String> httpResponse = httpClient.send(httpRequest, BodyHandler.asString());
System.out.println(httpResponse.body());
SYNC
ASYNC httpClient.sendAsync(httpRequest, BodyHandler.asString());

12. JAVA 9 - OTHER IMPROVEMENTS
▸ Collection improvement
▸ Compact String
▸ Multi Release JAR
▸ JVM based logging
▸ Try With Resource Improvement
▸ CompletableFuture API
▸ Stream API improvement

13. JAVA 9
▸ http://openjdk.java.net/jeps/0
▸ https://www.journaldev.com/13121/java-9-features-with-examples
▸ www.baeldung.com
▸ www.blog.idrsolutions.com
THANKS :)
https://github.com/AlicanAkkus/java9