The document discusses Project Jigsaw in JDK 9, which introduces modularity to Java, enhancing scalability, security, and maintainability. Key changes include the encapsulation of internal APIs and various structural updates to the JDK and JRE. The transition to a modular system involves new module declarations, dependencies, and application packaging requirements that developers will need to learn to adapt their code.

1. © Copyright Azul Systems 2016
© Copyright Azul Systems 2015
@speakjava azul.com
Project Jigsaw in JDK 9:
Modularity Comes To Java
Simon Ritter
Deputy CTO, Azul Systems
1

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4. © Copyright Azul Systems 2016
Agenda
§ API structure changes
§ Introduction to Jigsaw
§ Developing code with modules
§ Application migration
§ Resources
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5. © Copyright Azul Systems 2016
API Structure Changes

6. © Copyright Azul Systems 2016
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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7. © Copyright Azul Systems 2016
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
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8. © Copyright Azul Systems 2016
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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9. © Copyright Azul Systems 2016
Removed In JDK 9
§ Endorsed standard API override mechanism
§ Extension mechanism
§ No longer required now we have a module system
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10. © Copyright Azul Systems 2016
Binary Structure Of JDK/JRE
§ Potentially disruptive change
– Details in JEP 220
– Blurs the distinction between JRE and JDK
§ Implemented since late 2014
– Allow people to get used to new organisation
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11. © Copyright Azul Systems 2016
JDK Structure
bin
Pre-JDK 9 JDK 9
lib
tools.jar
jre
bin
rt.jar
lib
libconfbin
jre directory
tools.jar
rt.jar

12. © Copyright Azul Systems 2016
Most Popular Unsupported APIs
1. sun.misc.BASE64Encoder
2. sun.misc.Unsafe
3. sun.misc.BASE64Decoder
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Oracle dataset based on internal application code

13. © Copyright Azul Systems 2016
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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14. © Copyright Azul Systems 2016
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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15. © Copyright Azul Systems 2016
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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16. © Copyright Azul Systems 2016
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
...

17. © Copyright Azul Systems 2016
Introduction To Jigsaw And
Modules

18. © Copyright Azul Systems 2016
Goals For Project Jigsaw
§ Make Java SE more scalable and flexible
§ Improve security, maintainability and performance
§ Simplify construction, deployment and maintenance of
large scale applications
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19. © Copyright Azul Systems 2016
Modularity Specifications
§ Java Platform Module System
– JSR 376: Targeted for JDK 9 (no promises)
§ Java SE 9: New JSR will cover modularisation of APIs
§ OpenJDK Project Jigsaw
§ Reference implementation for JSR 376
§ JEP 200: The modular JDK
§ JEP 201: Modular source code
§ JEP 220: Modular run-time images
§ JEP 260: Encapsulate most internal APIs
§ JEP 261: Module system
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20. © Copyright Azul Systems 2016
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.Name
com.azul.zoop.alpha.Position
com.azul.zoop.beta.Animal
com.azul.zoop.beta.Zoo

21. © Copyright Azul Systems 2016
Module Declaration
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module com.azul.zoop {
}
module-info.java
com/azul/zoop/alpha/Name.java
com/azul/zoop/alpha/Position.java
com/azul/zoop/beta/Animal.java
com/azul/zoop/beta/Zoo.java

22. © Copyright Azul Systems 2016
Module Dependencies
module com.azul.zoop {
requires com.azul.zeta;
} com.azul.zoop
com.azul.zeta

23. © Copyright Azul Systems 2016
Module Dependencies
module com.azul.app {
requires com.azul.zoop
requires java.sql
}
com.azul.app
com.azul.zoop java.sql

24. © Copyright Azul Systems 2016
Module Dependency Graph
com.azul.app
java.base
java.sqlcom.azul.zoop
com.azul.zeta
java.xml java.logging

25. © Copyright Azul Systems 2016
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’);

26. © Copyright Azul Systems 2016
Module Readability Graph
com.azul.app
java.base
java.sqlcom.azul.zoop
com.azul.zeta
java.xml java.logging

27. © Copyright Azul Systems 2016
Package Visibility
module com.azul.zoop {
exports com.azul.zoop.alpha;
exports com.azul.zoop.beta;
}
com.azul.zoop
com.azul.zoop.alpha
com.azul.zoop.beta com.azul.zoop.theta

28. © Copyright Azul Systems 2016
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.app
reads

29. © Copyright Azul Systems 2016
Java Accessibility (pre-JDK 9)
public
protected
<package>
private

30. © Copyright Azul Systems 2016
Java Accessibility (JDK 9)
public to everyone
public, but only to specific modules
public only within a module
protected
<package>
private
public ≠ accessible (fundamental change to Java)

31. © Copyright Azul Systems 2016
JDK Platform Modules
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32. © Copyright Azul Systems 2016
Developing Code With
Modules

33. © Copyright Azul Systems 2016
Compilation
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$ javac –d mods
src/zeta/module-info.java
src/zeta/com/azul/zeta/Vehicle.java
mods/zeta/module-info.class
mods/zeta/com/azul/zeta/Vehicle.class
src/zeta/module-info.java
src/zeta/com/azul/zeta/Vehicle.java

34. © Copyright Azul Systems 2016
Module Path
$ javac –modulepath dir1:dir2:dir3

35. © Copyright Azul Systems 2016
Compilation With Module Path
33
$ javac –modulepath mods –d mods
src/zoop/module-info.java
src/zoop/com/azul/zoop/alpha/Name.java
mods/zoop/module-info.class
mods/zoop/com/azul/zoop/alpha/Name.class
src/zoop/module-info.java
src/zoop/com/azul/zoop/alpha/Name.java

36. © Copyright Azul Systems 2016
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

37. © Copyright Azul Systems 2016
Module Diagnostics
$ java –Xdiag:resolver –mp mods –m com.azul.zoop/com.azul.zoop.Main

38. © Copyright Azul Systems 2016
Packaging With Modular Jars
mods/zoop/module-info.class
mods/zoop/com/azul/app/Main.class
$ jar --create --file myLib/app.jar
--main-class com.azul.zoop.Main
-C mods .
module-info.class
com/azul/zoop/Main.class
app.jar

39. © Copyright Azul Systems 2016
Jar Files & Module Information
$ jar --file myLib/app.jar –p
Name:
com.azul.zoop
Requires:
com.azul.zeta
java.base [MANDATED]
java.sql
Main class:
com.azul.zoop.Main

40. © Copyright Azul Systems 2016
Application Execution (JAR)
$ java –mp myLib:mods –m com.azul.zoop.Main
Azul application initialised!

41. © Copyright Azul Systems 2016
Linking
Modular run-time
image
…confbin
jlink
$ jlink --modulepath $JDKMODS
--addmods java.base –output myimage
$ myimage/bin/java –listmods
java.base@9.0

42. © Copyright Azul Systems 2016
Linking An Application
$ jlink --modulepath $JDKMODS:$MYMODS
--addmods com.azul.app –output myimage
$ myimage/bin/java –listmods
java.base@9.0
java.logging@9.0
java.sql@9.0
java.xml@9.0
com.azul.app@1.0
com.azul.zoop@1.0
com.azul.zeta@1.0
Version numbering for
information purposes
only

43. © Copyright Azul Systems 2016
Application Migration

44. © Copyright Azul Systems 2016
Typical Application (JDK 8)
jar
jar
jar
JDK
jar
jarjar
jar jar
jar
jar
jar
jar

45. © Copyright Azul Systems 2016
Typical Application (JDK 9)
jar
jar
jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml
jar
jarjar
jar jar
jar
jar
jar
jar

46. © Copyright Azul Systems 2016
Sample Application
myapp.jar
lwjgl.jar
mylib.jar
gluegen-rt.jar jogl-all.jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml

47. © Copyright Azul Systems 2016
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

48. © Copyright Azul Systems 2016
Sample Application
module
myapp.jar
lwjgl.jar
module
mylib.jar
gluegen-rt.jar jogl-all.jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml

49. © Copyright Azul Systems 2016
Application module-info.java
module myapp {
requires mylib;
requires java.base;
requires java.sql;
requires lwjgl; ????
requires gluegen-rt; ????
requires jogl-all; ????
}

50. © Copyright Azul Systems 2016
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.datatransfer
module
java.xml

51. © Copyright Azul Systems 2016
Automatic Modules
§ Real modules
§ Reuse an existing JAR without change
§ Module name derived from JAR file name
§ Exports all its packages
– No selectivity
§ Requires all modules accessible from the module path
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52. © Copyright Azul Systems 2016
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.datatransfer
module
java.xml

53. © Copyright Azul Systems 2016
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 –mp mylib:lib –m myapp

54. © Copyright Azul Systems 2016
Summary & Further Information

55. © Copyright Azul Systems 2016
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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56. © Copyright Azul Systems 2016
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”
54

57. © Copyright Azul Systems 2016
Further Information
§ openjdk.java.net
§ openjdk.java.net/jeps
§ openjdk.java.net/projects/jigsaw
§ jcp.org
55

58. © Copyright Azul Systems 2016
© Copyright Azul Systems 2015
@speakjava azul.com
Questions
Simon Ritter
Deputy CTO, Azul Systems
56

59. Watch the video with slide
synchronization on InfoQ.com!
http://www.infoq.com/presentations/
jigsaw-jdk-9