jdk 9: big changes to make java smaller
TRANSCRIPT
© 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 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 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
weak module com.azul.zoop { requires com.azul.zeta;}
com.azul.zoop
com.azul.zoop.alphacom.azul.zoop.beta com.azul.zoop.theta
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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 –pName: com.azul.zoopRequires: com.azul.zeta java.base [MANDATED] java.sqlMain 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 –[email protected]
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Linking An Application
$ jlink --modulepath $JDKMODS:$MYMODS \ --addmods com.azul.app –output myimage
$ myimage/bin/java –[email protected]@[email protected]@[email protected]@[email protected]
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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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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