jdk 9: big changes to make java smaller

© Copyright Azul Systems 2016

© Copyright Azul Systems 2015

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JDK 9: Big Changes To Make Java Smaller

Simon RitterDeputy CTO, Azul Systems

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API Structural 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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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

JDK 8 has 18 interfaces, 23 classes, 64 fields, 358 methods and 20 constructors that have been deprecated

–None have been removed–Until now

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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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Removed In JDK 9 Endorsed standard API override mechanism Extension mechanism

No longer required now we have a module system

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Most Popular Unsupported APIs1. sun.misc.BASE64Encoder2. sun.misc.Unsafe3. sun.misc.BASE64Decoder

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Oracle dataset based on internal application 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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JEP 260 Accessible Critical APIs sun.misc.Unsafe sun.misc.Signal sun.misc.SignalHandler sun.misc.Cleaner sun.reflect.Reflection.getCallerClass sun.reflect.ReflectionFactory

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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) -> sun.misc.Unsafe -> ...

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Project Jigsaw And Modules

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Goals For Project Jigsaw Make Java SE more scalable and flexible

– Internet of Things– Microservices

Improve security, maintainability and performance

Simplify construction, deployment and maintenance of large scale applications

Eliminate classpath hell

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Module Fundamentals Module is a grouping of code

– For Java this is a collection of packages Modules 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.Reptilecom.azul.zoop.theta.Zoocom.azul.zoop.theta.Lake

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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/Reptile.javacom/azul/zoop/theta/Zoo.javacom/azul/zoop/theta/Lake.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 transitive 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 to com.azul.app;} com.azul.zoop

com.azul.zoop.alpha

com.azul.zoop.betacom.azul.zoop.thetacom.azul.app only

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More Package Visibility

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

com.azul.zoop

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

REFLECTIONGENERAL

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Even More Package Visibilitymodule com.azul.zoop { requires com.azul.zeta; exports com.azul.zoop.alpha; exports com.azul.zoop.beta to com.azul.app; exports private com.azul.theta;} com.azul.zoop

com.azul.zoop.thetaREFLECTIONGENERAL

com.azul.zoop.alpha

com.azul.zoop.betacom.azul.app only

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Restricted Keywords

module requires requires; exports exports;

module {

}

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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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Java Accessibility (pre-JDK 9)

publicprotected<package>private

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Java Accessibility (JDK 9)

public to everyonepublic, but only to specific modulespublic only within a module protected<package>private

public ≠ accessible (fundamental change to Java)

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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

no impliedreadability=

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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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Using Modules

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Module Path

$ javac –modulepath dir1:dir2:dir3

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Compilation With Module Path

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$ javac –modulepath mods –d mods \ src/module-info.java \ src/com/azul/zoop/alpha/Name.java

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

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

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Application Execution

-modulepath can be abbreviated to -mp

$ java –mp mods –m com.azul.app/com.azul.app.Main

Azul application initialised!

module name main class

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Packaging With Modular JAR Filesmods/module-info.classmods/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 –-print-module-descriptor

com.azul.zoop requires com.azul.zeta requires mandated java.base requires java.sql main-class com.azul.zoop.Main

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Application Execution (JAR)

$ java –mp mylib:mods –m com.azul.app

Azul application initialised!

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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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Sample Applicationmyapp.jar

libgl.jar

mylib.jar

gluegen.jar jogl.jar

modulejava.base

modulejava.desktop

modulejava.datatransfer

modulejava.xml

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Run Application With Classpath

$ java –classpath \ lib/myapp.jar: \ lib/mylib.jar: \ lib/libgl.jar: \ lib/gluegen.jar: \ lib/jogl.jar: \ myapp.Main

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Sample Applicationmodule

myapp.jar

libgl.jar

modulemylib.jar

gluegen.jar jogl.jar

modulejava.base

modulejava.desktop

modulejava.datatransfer

modulejava.xml

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Application module-info.java

module myapp { requires mylib; requires java.base; requires java.sql; requires libgl; ???? requires gluegen; ???? requires jogl; ????}

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Sample Applicationmodule

myapp.jar

modulelibgl.jar

modulemylib.jar

modulegluegen.jar

modulejogl.jar

modulejava.base

modulejava.desktop

modulejava.datatransfer

modulejava.xml

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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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Application Module Dependenciesmodule

myapp.jar

modulelibgl.jar

modulemylib.jar

modulegluegen.jar

modulejogl.jar

modulejava.base

modulejava.desktop

modulejava.datatransfer

modulejava.xml

ImplicitExplicit

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Run Application With Modules

$ java –classpath \ lib/myapp.jar: \ lib/mylib.jar: \ lib/libgl.jar: \ lib/gluegen.jar: \ lib/jogl.jar: \ myapp.Main

$ java –mp mylib:lib –m myapp

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Advanced Details

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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)

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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

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

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Classloaders (Since JDK 1.2)

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Bootstrap classloader (Internal Class)Bootstrap Class Path

Extension classloader (URLClassLoader) Extension Mechanism

Application classloader (URLClassLoader) Class Path

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Classloaders (JDK 9)

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Bootstrap classloader (Internal Class) bootstrap class path

Platform classloader (Internal Class) JDK classes with specific permissions

Application classloader (Internal Class) Class & Module Path

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Services

module java.sql { requires transient java.logging; requires transient java.xml; exports java.sql; exports javax.sql; exports javax.transaction.xa; uses java.sql.Driver;}

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Services

module com.mysql.jdbc { requires java.sql; exports com.mysql.jdbc; provides java.sql.Driver with com.mysql.jdbc.Driver;}

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Summary

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

– Graphing of dependencies

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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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Zulu.org Azul binary distribution of OpenJDK source code Passed all TCK tests Completely FREE!

– Pay us if you’d like enterprise level support Just announced: Embedded Zulu support for ARM 32-bit

– Intel already supported– “Requires no licensing fee”

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

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Questions

Simon RitterDeputy CTO, Azul Systems

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