Modularization With Project Jigsaw in JDK 9

© Copyright Azul Systems 2016
@speakjava
Modularization with Project
Jigsaw in JDK 9
Simon Ritter
Deputy CTO, Azul Systems
1

Agenda
 JDK 9 API structure overview
 Introduction to Jigsaw and modules
 Developing code with modules
 Summary and further information
2

JDK 9 API Structure Overview
3

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
 See how long you can keep a project going for
4

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
5

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
6

JDK 9: Incompatible Changes
 Encapsulate most JDK internal APIs
 Remove a small number of supported APIs
– 6 in total, all add/remove PropertyChangeListener
 Change the binary structure of the JRE and JDK
 Remove the endorsed-standards override and extension
mechanism
 New version string format
 A single underscore will no longer be allowed as an
identifier in source code
7

Most Popular Unsupported APIs
1. sun.misc.BASE64Encoder
2. sun.misc.Unsafe
3. sun.misc.BASE64Decoder
8
Oracle dataset based on internal application code

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
9

JEP 260 Proposal
1. Encapsulate all non-critical JDK-internal APIs
2. Encapsulate all critical JDK-internal APIs, for which
supported replacements exist in JDK 8
3. 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
10

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
11

JDK Structure
bin
Pre-JDK 9 JDK 9
lib
tools.jar
jre
bin
rt.jar
lib
libconfbin
jre directory
tools.jar
rt.jar

Introduction to Jigsaw and Modules
13

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
14
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
15
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

Module Dependencies
requires com.azul.zeta;
} com.azul.zoop
com.azul.zeta

Module Dependencies
module com.azul.app {
requires com.azul.zoop;
requires java.sql;
}
com.azul.app
com.azul.zoop java.sql

Module Dependency Graph
com.azul.app
java.base
java.sqlcom.azul.zoop
com.azul.zeta
java.xml java.logging

Package Visibility
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

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

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’);

Module Readability Graph
com.azul.app
java.base
java.sqlcom.azul.zoop
com.azul.zeta
java.xml java.logging

Java Accessibility (pre-JDK 9)
public
protected
<package>
private

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)

JDK Platform Modules
25

Developing Code With Modules
26

Compilation
27
$ javac –d mods
src/zeta/module-info.java
src/zeta/com/azul/zeta/Vehicle.java
mods/zeta/mod-info.class
mods/zeta/com/azul/zeta/Vehicle.class
src/zeta/mod-info.java
src/zeta/com/azul/zeta/Vehicle.java

Module Path
$ javac –modulepath dir1:dir2:dir3

Compilation With Module Path
29
$ javac –modulepath mlib –d mods
src/zoop/module-info.java
src/zoop/com/azul/zoop/alpha/Name.java
mods/zoop/mod-info.class
mods/zoop/com/azul/zoop/alpha/Name.class
src/zoop/mod-info.java
src/zoop/com/azul/zoop/alpha/Name.java

Application Execution
 -modulepath can be abbreviated to -mp
$ java –modulepath mods –m com.azul.app/com.azul.app.Main
Azul application initialised!
module name main class

Packaging With Modular Jars
mods/app/mod-info.class
mods/app/com/azul/app/Main.class
$ jar --create --file mlib/app.jar
--main-class com.azul.app.Main
-C mods .
module-info.class
com/azul/zoop/Main.class
app.jar

Jar Files & Module Information
$ jar --file mlib/app.jar –p
Name:
com.azul.app
Requires:
com.azul.zoop
java.base [MANDATED]
java.sql
Main class:
com.azul.app.Main

Application Execution (JAR)
$ java –mp mlib:mods –m com.azul.app.Main
Azul application initialised!

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

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

Summary & Further Information
36

Summary
 Modularisation is a big change for Java
– JVM/JRE rather than language/APIs
– Public access isn’t necessarily the same
 Flexibility to define what is exported
 New linking capability to generate runtime image
 More to learn about converting existing code
 Will make all applications simpler to deploy and manage
37

Further Information
 openjdk.java.net
 openjdk.java.net/jeps
– 200, 201, 220, 260, 261
 openjdk.java.net/projects/jigsaw
 jcp.org
– JSR 376
 www.zulu.org (OpenJDK supported builds JDK 6, 7, 8, 9)
 www.azul.com (Zing JVM for low latency)
38

@speakjava
Modularization with Project
Jigsaw in JDK 9
Simon Ritter
Deputy CTO, Azul Systems
39

Modularization With Project Jigsaw in JDK 9

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