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© Copyright Azul Systems 2015

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Project Jigsaw in JDK 9:Modularity Comes To Java

Simon RitterDeputy CTO, Azul Systems

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API Structure Changes

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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

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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

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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

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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

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Reviewing Your Own Code jdeps tool

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

jdeps –jdkinternals path/myapp.jar

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

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Introduction To Jigsaw And Modules

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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

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com.azul.zoop

com.azul.zoop.alpha.Namecom.azul.zoop.alpha.Positioncom.azul.zoop.beta.Animalcom.azul.zoop.beta.Zoo

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Module Declaration

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module com.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

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Module Dependencies

module com.azul.zoop { requires com.azul.zeta;}

com.azul.zoop

com.azul.zeta

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Module Dependencies

module com.azul.app { requires com.azul.zoop requires java.sql}

com.azul.app

com.azul.zoop java.sql

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Module Dependency Graphcom.azul.app

java.base

java.sqlcom.azul.zoop

com.azul.zetajava.xml java.logging

explicitimplicit

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Readability v. Dependency

com.azul.app

java.sql

java.logging

module java.sql { requires public java.logging;}

Driver d = …Logger l = d.getParentLogger();l.log(“azul’);

Implied readability

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Module Implied Readability Graphcom.azul.app

java.base

java.sqlcom.azul.zoop

com.azul.zetajava.xml java.logging

explicitimplicitimplied

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Package Visibility

module com.azul.zoop { requires com.azul.zeta; exports com.azul.zoop.alpha; exports com.azul.zoop.beta;} com.azul.zoop

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

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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.zoopcom.azul.appreads

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JDK 8 Dependencies

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JDK 9 Platform Modules

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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.managementjava.security.jgss

java.naming

java.security.sasl

All modules depend on java.base

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JDK 9 Platform Modules

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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

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Developing Code With Modules

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

$ jar --create --file mylib/app.jar \ --main-class com.azul.app.Main \ -C mods .

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

app.jar

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JAR Files & Module Information

$ jar --file mylib/app.jar –pName: com.azul.zoopRequires: com.azul.zeta java.base [MANDATED] java.sqlMain class: com.azul.zoop.Main

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LinkingModular run-time

image

…confbin

jlink

$ jlink --modulepath $JDKMODS \ --addmods java.base –output myimage

$ myimage/bin/java –listmodsjava.base@9.0

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Linking An Application

$ jlink --modulepath $JDKMODS:$MYMODS \ --addmods com.azul.app –output myimage

$ 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 forinformation purposes only“It is not a goal of the module system to solve the version-

selection problem”

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Application Migration

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Typical Application (JDK 8)

jarjar

jar

JDK

jar

jarjarjar jar

jarjar

jar

jar

Cla

sspa

th

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Typical Application (JDK 9)

jarjar

jar

modulejava.base

modulejava.desktop

modulejava.datatransfer

modulejava.xml

jar

jarjarjar jar

jarjar

jar

jar

Unnamed module

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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

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Summary & Further Information

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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

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

www.zulu.org

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Questions

Simon RitterDeputy CTO, Azul Systems

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