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Modules in Java? Finally!
Jigsaw

What is this talk all about? (Agenda)
? This talk is for a very important new feature in Java SE 9
? Code named Jigsaw, this feature modularizes the Java SE platform
? Agenda
? Who am I?
? Problems with monolithic java
? Solutions in Java SE 9
? Jigsaw in examples
? JDK9 Early Access with Jigsaw
? A modular example, transitivity
? Services and Custom JREs

Who am I? @mihailstoynov
? By day: sty.bz
? Java
? Security audits, web pen testing, sec tools
? Training, travelling ->
? By night: jug.bg
? Java evangelism
? Submitting Java patches, writing manuals,
early adoption
? jprime.io �C organize big java conf in Sofia
? Co-authoring books, university courses
? Weekends
? Bikes

Problems with a monolithic Java

Why do we need jigsaw? 1
? "Small" devices can run Java,
but JRE size is a problem
? Clouds don't like wasting resources
loading a large JRE full of
unnecessary classes

? JDK is messy

? Classpath is messy

? People use sun.misc.* or *.internal.* APIs, which was not intended
? Securing the platform is difficult if everyone can read anything

Problem: source code is monolithic 201
? JRE source code itself is monolithic �C it has no modules
? Solution (JEP 201)
? Reorganize mercurial repo
? src/share/classes/java/lang/Object.java
src/share/native/java/lang/Object.c
->
src/java.base/share/classes/java/lang/Object.java
src/java.base/share/native/java/lang/Object.c
? Rename solaris to unix
? Compile repo -> compile modules
? Enforce module boundaries at build time

Problem: JRE code is not modular 200
? JRE itself is not using modules
? Create modules for code governed by JCP (module java.base)
? Modules for other code in the JDK (module jdk.javadoc )
? Define requires public
? All reside in $JAVA_HOME/jmods

Offtopic: jmods are not for you
? .jmod format was created for the platform
? can have native code
? Overall very cool
? $ jmod list $JAVA_HOME/jmods/java.base.jmod
--list of classes��-
--native code too (so, dylib)--
? $ jmod describe $JAVA_HOME/jmods/java.base.jmod
? Describes what it exports, what it conceals, who it exports it too
and stuff

Problem: JRE code is not modular 200
Check out the java.compact{1..3}

Problem: Internal APIs 260
? Many are using internal APIs (example: sun.misc.Unsafe)
? Provide safe alternative (other JEPs)
? Non critical (Base64Decoder) are encapsulated or deprecated
? Critical APIs (Unsafe) are rewritten and encapsulated (JEP 259)

Problem: JRE is too big 282
? The JRE is too big
? Some distributions are over 100MB
? In mobile devices: CPU is strong enough for java, but little space
? In Java 9 we can create a "custom runtime image"
? A tool that can do that is called jlink
? The same tool can also add our
application modules
? Only the ones we need

Problem: Put it all together 261 (376)
? JSR 376 (Java Platform Module System) proposes changes and
extensions to
? the Java programming language
? the Java virtual machine
? the standard Java APIs
? JSR 376 Will be implemented in JEP 261
? JCP = Java Community Process (IBM, SAP, RedHat "participate")
? JSR = Java Specification Request (specifies new standards, JCP)
? JEP = Java Enhancement Process (implementations, non JCP)

More problems
? The base classes had a lot of cyclic dependencies
? They had to be unwounded
? It took several years to specify the module format
? Several abandoned formats so far
? It took several years to specify the scope of Jigsaw
? For example no dynamic loading/unloading
? No luck for OSGi
? Mark Reinhold said that this will not be implemented soon

JDK9 Early Access with Jigsaw
? jdk9.java.net/jigsaw

pre-Java9 class visibility
? Until Java 9 a class had the following visibility "levels":
? public
? friendly, package private (includes protected)
? protected
? private

post-Java9 class visibility
? In Java 9 new levels of "public" are provided:
? public
? To all
? To some modules (we specify them)
? Only to our module
? friendly, package private (includes protected)
? protected
? private

Creating a simple module bz.sty.logger
? Important note: just like packages, module names are dir names
? module-info.java
module bz.sty.logger {
requires java.base; //implicit
exports bz.sty.logger;
}
? Logger.java
package bz.sty.logger;
public class Logger {
public void log(String message) {
System.out.println("Logger: "+message);
}
}
? Compilation
$ javac -d mods/
Logger/bz.sty.logger/bz/sty/logger/Logger.java
Logger/bz.sty.logger/module-info.java

Referencing the log module bz.sty.main
? module-info.java:
module bz.sty.main {
requires bz.sty.logger; //implicit
//exports bz.sty.logger;
}
? Program.java
public class Program {
public void main(String... args) {
new Logger.log("Hello, World!");
}
}
? Compilation
$ javac -d mods
-modulepath mods/
Main/bz.sty.main/bz/sty/main/Program.java
Main/bz.sty.main/module-info.java

Compile multiple modules at once
$ javac
-d mods/
-modulesourcepath Logger/:Main/
$(find Logger/ Main/ -name *.java)
? What did we do here?
? All source paths are in modulesourcepath
? We use a bit of bash magic to add all java files
? All should be deployed

Running a multi module app
$ java
-modulepath mods/
-m bz.sty.main/bz.sty.main.Program
Logger: Hello, World!

Support for Jigsaw
? Maven, Gradle
? None
? IntelliJ IDEA, Eclipse
? None
? I use IDEA modules and duplicate the dependencies
? NetBeans
? http://wiki.netbeans.org/JDK9Support
? But I don't like it, so we won't use it
? When will it be released
? With Java SE 9
? Used to be mid'2016, jigsaw delayed it to Q1'2017
? http://www.java9countdown.xyz/
? Nobody believes it will be on time

Packaging
$ mkdir mlib
$ jar --create
--file=mlib/bz.sty.logger@2.0.jar
--module-version=199.0
-C mods/bz.sty.logger .
$ jar --create
--file=mlib/bz.sty.main.jar
--main-class=bz.sty.main.Program
-C mods/bz.sty.main .
$ java -mp mlib -m bz.sty.main
Logger: Hello, World!

What's in the jar?
$ jar --print-module-descriptor
--file=mlib/bz.sty.main.jar
bz.sty.main
requires bz.sty.logger
requires mandated java.base
conceals bz.sty.main
main-class bz.sty.main.Program
$ jar --print-module-descriptor
--file=mlib/bz.sty.logger@2.0.jar
bz.sty.logger@199.0
requires java.base
exports bz.sty.logger

Transitivity ("requires public")
? We create a new module, called prettylogger
? public class PrettyLogger extends Logger
? We change dependencies so that main ? prettylogger ? logger
? The new main:
public class Program {
public static void main(String... args) {
Logger logger = new PrettyLogger();
logger.log("Hello, World!");
}
}
? module-info.java
module bz.sty.prettylogger {
requires public bz.sty.logger;
exports bz.sty.prettylogger;
}

Quering the JDK module system
? $ java �Clistmods
? List all modules in the JDK
? Shows the version
? $ jmod describe $JAVA_HOME/jmods/java.base.jmod
? Shows a very detailed description
? $ jmod list $JAVA_HOME/jmods/java.base.jmod
? A list of all classes in the jmod

Services
? Services allow for loose coupling between service
consumers modules and service providers modules
? Since Java SE 6, ServiceLoader API allows extending applications
? SL detects implementations of an interface and loads them
? This solution still works nicely with Java modules
? It is now sufficient the modules to be present on module-path
? Basically we define an interface/abstract class and we state that we
depend on their implementations
? we cant run without an implementation
? Other modules implement that interface/abstract class
? All is defined in the module-info

The module and the provider
module bz.sty.pluggablelogger {
exports bz.sty.pluggablelogger;
exports bz.sty.pluggablelogger.spi;
uses bz.sty.pluggablelogger.spi.PluggableLoggerProvider;
}
public abstract class PluggableLoggerProvider {
protected PluggableLoggerProvider() { }
public abstract PluggableLogger getPluggableLogger();
}

PluggableLogger
public abstract class PluggableLogger {
public static PluggableLogger get() {
ServiceLoader<PluggableLoggerProvider> sl
= ServiceLoader.load(PluggableLoggerProvider.class);
Iterator<PluggableLoggerProvider> iter = sl.iterator();
if (!iter.hasNext())
throw new RuntimeException("No service providers found!");
PluggableLoggerProvider provider = iter.next();
return provider.getPluggableLogger();
}
protected PluggableLogger() { }
public abstract void log(String message);
}

SuperLogger (implementing module)
module bz.sty.superlogger {
requires bz.sty.pluggablelogger;
exports bz.sty.superlogger;
provides bz.sty.pluggablelogger.spi.PluggableLoggerProvider
with bz.sty.superlogger.SuperLoggerProvider;
}
public class SuperLoggerProvider extends PluggableLoggerProvider {
public PluggableLogger getPluggableLogger() {
return new SuperLogger();
}
}
public class SuperLogger extends PluggableLogger {
public void log(String message) {
System.out.println("SuperLogger: " + message);
}
}

Running it all together
$ javac -d mods �Cmodulesourcepath
PluggableLogger:PluggableLoggerImpl:PluggableLoggerMain
$(find Pluggable* -name *.java)
$ jar --create --file=X.jar �CC mods/mdl .
$ java -mp mlib/ -m bz.sty.pluggableloggerexample
SuperLogger: Hello, World!
$ java -Xdiag:resolver

Jigsaw in examples
Custom JREs
(Jlink)

Create a custom JRE
? And now a drum roll for the coolest feature
? We hinted that it's now possible to create custom JREs
? The tool is called JLINK
? jlink takes the smallest set of needed jars and jmods and creates a
new JRE in a dir. Very WOW

jlink in action (example)
$ jlink --modulepath $JAVA_HOME/jmods:mlib
--addmods bz.sty.pluggablelogger,
bz.sty.superlogger,
bz.sty.pluggableloggerexample
--output CustomVM
$ CustomVM/bin/java -listmods
$ CustomVM/bin/java -m bz.sty.pluggableloggerexample
SuperLogger: Hello, World!
$ du �Csh CustomVM/
30M
$ du -sh $JAVA_HOME
408M

Stuff we didn't discuss, but it's important
? Jdeps
? A tool to check if you use internal APIs
? Unnamed modules
? All old jars
? Automatic modules
? Making old jars to modules
? Migrating an application gradually
? Not difficult at all, but only after IntelliJ/Eclipse and maven support
? The console is difficult
? Mixing --classpath and --modulepath
? It takes some getting used to

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Modules in Java? Finally! (OpenJDK 9 Jigsaw, JSR376)

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