Project Jigsaw in JDK 9: Modularity Comes To Java

@speakjava azul.com

Simon Ritter Deputy CTO, Azul Systems

Agenda § API structure changes §  Introduction to Jigsaw § Developing code with modules § Application migration § Advanced stuff § Summary & Further Information

API Structure Changes

API Classification § Supported, intended for public use

– JCP specified: java.*, javax.* – JDK specific: some com.sun.*, some jdk.*

§ Unsupported, not intended for public use – Mostly sun.* – Most infamous is sun.misc.Unsafe

General Java Compatability Policy § If an application uses only supported APIs on version N of

Java it should work on version N+1, even without recompilation

§ Supported APIs can be removed, but only with advanced notice

§ To date 23 classes, 18 interfaces and 379 methods have been deprecated

– None have been removed

JDK 9: Incompatible Changes § Encapsulate most JDK internal APIs § Remove a small number of supported APIs

– 6 in total, all add/remove PropertyChangeListener – Already flagged in JSR 337 (Java SE 8), JEP 162

§ Change the binary structure of the JRE and JDK § New version string format § A single underscore will no longer be allowed as an

identifier in source code

Removed In JDK 9 § Endorsed standard API override mechanism § Extension mechanism

§ No longer required now we have a module system

JDK Internal API Classification § Non-critical

– Little or no use outside the JDK – Used only for convenience (alternatives exist)

§ Critical – Functionality that would be difficult, if not impossible to

implement outside the JDK

JEP 260 Proposal § Encapsulate all non-critical JDK-internal APIs § Encapsulate all critical JDK-internal APIs, for which

supported replacements exist in JDK 8 § Do not encapsulate other critical JDK-internal APIs

– Deprecate these in JDK 9 – Plan to encapsulate or remove them in JDK 10 – Provide command-line option to access encapsulated

critical APIs

JEP 260 Accessible Critical APIs § sun.misc.Unsafe § sun.misc.Signal § sun.misc.SignalHandler § sun.misc.Cleaner § sun.reflect.Reflection.getCallerClass § sun.reflect.ReflectionFactory

Reviewing Your Own Code §  jdeps tool

– Introduced in JDK 8, improved in JDK 9 – Maven jdeps plugin

jdeps–jdkinternalspath/myapp.jar

path/myapp.jar->/opt/jdk1.8.0/jre/lib/rt.jar<unnamed>(myapp.jar)->java.awt->java.awt.event->java.beans->java.io...

Introduction To Jigsaw And Modules

Goals For Project Jigsaw §  Make Java SE more scalable and flexible

–  IoT devices need more compact Java runtimes §  Improve security, maintainability and performance

§  Simplify construction, deployment and maintenance of large scale applications

§  Eliminate classpath hell

Module Fundamentals § Module is a grouping of code

– For Java this is a collection of packages § The module can contain other things

– Native code – Resources – Configuration data

com.azul.zoop

com.azul.zoop.alpha.Name com.azul.zoop.alpha.Position com.azul.zoop.beta.Animal com.azul.zoop.beta.Zoo

Module Declaration

modulecom.azul.zoop{}

module-info.javacom/azul/zoop/alpha/Name.javacom/azul/zoop/alpha/Position.javacom/azul/zoop/beta/Animal.javacom/azul/zoop/beta/Zoo.java

Module Dependencies

modulecom.azul.zoop{requirescom.azul.zeta;} com.azul.zoop

com.azul.zeta

Module Dependencies

modulecom.azul.app{requirescom.azul.zooprequiresjava.sql}

com.azul.app

com.azul.zoop java.sql

Module Dependency Graph com.azul.app

java.base

java.sql com.azul.zoop

com.azul.zeta java.xml java.logging

explicit implicit

Readability v. Dependency

com.azul.app

java.sql

java.logging

modulejava.sql{requirespublicjava.logging;}

Driverd=…Loggerl=d.getParentLogger();l.log(“azul’);

Implied readability

Module Implied Readability Graph com.azul.app

java.base

java.sql com.azul.zoop

com.azul.zeta java.xml java.logging

explicit implicit implied

Package Visibility

modulecom.azul.zoop{requirescom.azul.zeta;exportscom.azul.zoop.alpha;exportscom.azul.zoop.beta;}

com.azul.zoop

com.azul.zoop.alphacom.azul.zoop.beta com.azul.zoop.theta

Accessibility § For a package to be visible

– The package must be exported by the containing module – The containing module must be read by the using module

§ Public types from those packages can then be used

com.azul.zoop com.azul.app

Java Accessibility (pre-JDK 9)

publicprotected<package>private

Java Accessibility (JDK 9)

publictoeveryonepublic,butonlytospecificmodulespubliconlywithinamoduleprotected<package>private

public ≠ accessible (fundamental change to Java)

JDK 8 Dependencies

JDK 9 Platform Modules

java.se

java.compact3

java.compact2

java.compact1

java.scripting

java.instrument

java.base

java.logging

java.sql

java.sql.rowset

java.xml

java.desktop

java.rmi

java.prefs java.datatransfer

java.compiler

java.management java.security.jgss

java.naming

java.security.sasl

All modules depend on java.base

JDK 9 Platform Modules

java.se.ee java.se

java.xml.bind

java.corba

java.compiler

java.desktop

java.annotations.common

java.rmi

java.datatransfer

java.management

java.xml.ws

java.naming

java.transaction

java.activation

All modules depend on java.base

Developing Code With Modules

Compilation

$javac–dmods\src/zeta/module-info.java\src/zeta/com/azul/zeta/Vehicle.java

mods/zeta/module-info.classmods/zeta/com/azul/zeta/Vehicle.class

src/zeta/module-info.javasrc/zeta/com/azul/zeta/Vehicle.java

Module Path

$javac–modulepathdir1:dir2:dir3

Compilation With Module Path

$javac–modulepathmods–dmods\src/zoop/module-info.java\src/zoop/com/azul/zoop/alpha/Name.java

mods/zoop/module-info.classmods/zoop/com/azul/zoop/alpha/Name.class

src/zoop/module-info.javasrc/zoop/com/azul/zoop/alpha/Name.java

Application Execution

§ -modulepath can be abbreviated to -mp

$java–mpmods–mcom.azul.app/com.azul.app.MainAzulapplicationinitialised!

module name main class

Packaging With Modular JAR Files mods/zoop/module-info.classmods/zoop/com/azul/app/Main.class

$jar--create--filemylib/app.jar\--main-classcom.azul.app.Main\-Cmods.

module-info.classcom/azul/app/Main.class

app.jar

JAR Files & Module Information

$jar--filemylib/app.jar–pName:com.azul.zoopRequires:com.azul.zetajava.base[MANDATED]java.sqlMainclass:com.azul.zoop.Main

Application Execution (JAR)

$java–mpmylib:mods–mcom.azul.appAzulapplicationinitialised!

Linking Modular run-time

… conf bin

$jlink--modulepath$JDKMODS\--addmodsjava.base–outputmyimage$myimage/bin/java–listmodsjava.base@9.0

Linking An Application

$jlink--modulepath$JDKMODS:$MYMODS\--addmodscom.azul.app–outputmyimage$myimage/bin/java–listmodsjava.base@9.0java.logging@9.0java.sql@9.0java.xml@9.0com.azul.app@1.0com.azul.zoop@1.0com.azul.zeta@1.0

Version numbering for information purposes only “It is not a goal of the module system to solve the version-

selection problem”

Application Migration

Typical Application (JDK 8)

jar jar

jar jar jar jar

jar jar

Typical Application (JDK 9)

jar jar

module java.base

module java.desktop

module java.datatransfer

module java.xml

jar jar jar jar

jar jar

Unnamed module

Sample Application myapp.jar

lwjgl.jar

mylib.jar

gluegen-rt.jar jogl-all.jar

module java.base

module java.desktop

module java.xml

Run Application With Classpath

$java–classpath\lib/myapp.jar:\lib/mylib.jar:\lib/liblwjgl.jar:\lib/gluegen-rt.jar:\lib/jogl-all.jar:\myapp.Main

Sample Application module

myapp.jar

lwjgl.jar

module mylib.jar

gluegen-rt.jar jogl-all.jar

module java.base

module java.desktop

module java.xml

Application module-info.java

modulemyapp{requiresmylib;requiresjava.base;requiresjava.sql;requireslwjgl;????requiresgluegen-rt;????requiresjogl-all;????}

Sample Application module

myapp.jar

module lwjgl.jar

module mylib.jar

module gluegen-rt.jar

module jogl-all.jar

module java.base

module java.desktop

module java.xml

Automatic Modules § Real modules § Simply place unmodified jar file on module path

– Rather than classpath § No changes to JAR file § Module name derived from JAR file name § Exports all its packages

– No selectivity § Automatically requires all modules on the module path

Application Module Dependencies module

myapp.jar

module lwjgl.jar

module mylib.jar

module gluegen-rt.jar

module jogl-all.jar

module java.base

module java.desktop

module java.xml

Implicit Explicit

Run Application With Modules

$java–classpath\lib/myapp.jar:\lib/mylib.jar:\lib/liblwjgl.jar:\lib/gluegen-rt.jar:\lib/jogl-all.jar:\myapp.Main$java–mpmylib:lib–mmyapp

Advanced Stuff

Modular Jar Files And JMODs § Modular jar files are simple

– Standard jar file possibly with module-info.class file – Can use existing (unmodified) jar files

§ JMOD files – More complex module files – Used for modules in the JDK – Can include native files (JNI), configuration files and other

data – Based on zip file format (pending final details - JEP 261)

jmod Command

§ Create can specify several details: – Main class – Native libraries and commands – Configuration data – OS name, version and machine architecture

§ Details included in module-info.class file

jmod(create|list|describe)<options><jmod-file>

Classloaders (Since JDK 1.2)

Bootstrap classloader (Internal Class) Bootstrap Class Path

Extension classloader (URLClassLoader) Extension Mechanism

Application classloader (URLClassLoader) Class Path

Classloaders (JDK 9)

Bootstrap classloader (Internal Class) bootstrap class path

Platform classloader (Internal Class) JDK classes with specific permissions

Application classloader (Internal Class) Class & Module Path

Summary & Further Information

Tooling Support § NetBeans leads the way § Early Access NetBeans 9 available § Support for module-info.java file

– Graphing of dependencies

NetBeans Tooling

Summary § Modularisation is a big change for Java

– JVM/JRE rather than language/APIs § Potentially disruptive changes to exposure of non-public APIs

– Is it safe? § Developing modular code will require some learning

– Not a huge change, though

Further Information § openjdk.java.net § openjdk.java.net/jeps § openjdk.java.net/projects/jigsaw §  jcp.org

§ www.zulu.org

@speakjava azul.com

Questions

Simon Ritter Deputy CTO, Azul Systems

Project Jigsaw in JDK 9: Modularity Comes To Java · Project Jigsaw in JDK 9: Modularity Comes To...

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