jdk-9: modules and java linker

JDK-9 Modules and Java Linker (JLink)

G. Bhanu Prakash

Java Platform Team

Oracle India Private Limited

bhanu.prakash.gopularam@oracle.com

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Agenda 1. Modules

2. Module Dependencies

3. Jlink and Packaging

4. Jlink Plugins

5. Example Plugins 1. System Module Descriptor Plugin

2. Compress Plugin

3. Release-Info Plugin

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SAFE HARBOR STATEMENT

The following is intended to outline our general product direction. It is intended for information purpose only, and may not be incorporated in any contract. It is not a commitment to deliver any material, code, or

functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or

functionality described for Oracle’s products remains at the sole discretion of Oracle

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Jigsaw Problems Problems

Platform scalability (small devices)

Jar Hell or Classpath Hell

• Java runtime crashes with NoClassDefFoundError

• Shadowing of classes

Performance

• Startup

• Download

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Jigsaw Solutions Problems

Platform scalability

• Modularize JDK

Jar Hell or Classpath Hell

• Replace classpath with module dependencies

Performance

• Startup – install optimizations in module library

• Download - incremental modules in demand

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• What is Module

• Module-Info.java – Visibility Rules

• REQUIRES

• EXPORTS

• REQUIRES PUBLIC

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Modules

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“public” no longer means “accessible”

Modules

com.foo.app module-info.java module com.foo.app { requires com.foo.bar; requires java.sql; }

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Example: com.foo.app

Modules Example

com.foo.bar module com.foo.app { exports com.foo.bar; }

Actual Module Dependencies (com.foo.app)

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Transitive Dependencies (com.foo.app)

JDK Platform Modules

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How to compile modules

Inputs Jmods, Modular jar files

Exploded modules

1. Compile com.foo.bar (base)

javac -d mods\com.foo.bar

src\com.foo.bar\module-info.java

src\com.foo.bar\com\foo\bar\*.java

2. Compile com.foo.app (main application)

javac -modulepath mods

-d mods\com.foo.app

src\com.foo.app\module-info.java

src\com.foo.app\com\foo\app\*.java

Or

javac –modulesourcepath src –d mods …

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Create Modules

Create module com.foo.bar

jmod create

--class-path mods\com.foo.bar

com.foo.bar

Create module com.foo.app jmod create

--class-path mods\com.foo.app

com.foo.app

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Module Information

• jmod describe com.foo.bar com.foo.bar

requires mandated java.base

exports com.foo.bar

• jmod describe com.foo.app com.foo.app

requires com.foo.bar

requires mandated java.base

requires java.sql

conceals com.foo.app

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Linking

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Jlink and Packaging (JEP-282)

Brief History Jrecreate was introduced in Java 8 with EJDK (JavaSE Embedded)

Instead of binaries we ship the EJDK

Jlink Usage: Command line tool to link module modules into jimage file

generate runtime images

JEP-282: “Link time is an opportunity to do whole-world optimizations that are otherwise difficult at compile or costly at runtime”

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Jlink Packaging

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Legacy JDK image

JDK-9 Generated Image

Jlink Packaging

Create image file

jlink --output myimage

--addmods com.foo.app

--modulepath jdk-9b131\jmods;mods

>ls myimage

bin lib conf release

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App execution from Generated image

>myimage\bin\java -listmods

com.foo.app

com.foo.bar

java.base@9-ea

java.logging@9-ea

java.sql@9-ea

java.xml@9-ea

>java -m com.greetings/com.greetings.Main

Output: Greetings (com.foo.app.Main) : World (from com.foo.bar)

>java -m com.foo.app/com.foo.app.App2

Output: Exception:oracle.jdbc.driver.OracleDriver

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-modulepath mods Not required

Jlink Plugins

Image customization enabled using a set of predefined plugins

12 builtin plugins. Example: compress-resources

release-info

sort-resources

exclude-files

gen-installed-modules

replace-file

Programmatic access to jlink features

As per the JEP, the plugin API is strictly experimental

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Plugins and Image creation - WorkFlow

Optimizing Java startup Problem: Significant time spent parsing and validating

module-info.class for each module in system image itself

Solution: Implement jlink plugin to generate a pre-

validated system module graph

SystemModuleDescriptorPlugin

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--installed-modules Startup time

Disabled 510 ms

Enabled 220 ms

• Reduces memory use by a sizable amount

• This plugin is ON by default (--installed-modules on)

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Compress Plugin

LEVEL_0

StringSharingPlugin - Scans image classes constant pool (UTF-8 Strings)

LEVEL_1:

ZipPlugin(resFilter) - Zip compression of image classes

LEVEL_2:

StringSharingPlugin(resFilter)

ZipPlugin(resFilter)

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Compression level

Size (~)

None 28.5 MB

LEVEL_0 17.3 MB

LEVEL_1 11.7 MB

LEVEL_2 11.5 MB

Table: Jlink generated image size

Release-info Plugin

Normal JDK myimage>cat release

#Wed Aug 24 09:19:38 IST 2016 MODULES=java.sql,com.foo.bar,com.foo.app,java.logging,java.xml,java.base OS_VERSION=5.2 OS_ARCH=amd64 OS_NAME=Windows JAVA_VERSION=9-ea

With Release Plugin: jlink --release-info

add:build_type=fastdebug,source=oraclejdk,java_version=9+101 …

myimage2>cat release #Wed Aug 24 09:32:36 IST 2016 MODULES=java.sql,com.foo.bar,com.foo.app,java.logging,java.xml,java.base OS_VERSION=5.2 OS_ARCH=amd64 OS_NAME=Windows JAVA_VERSION=9-ea

build_type=fastdebug,source\=oraclejdk,java_version\=9+101

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Summary

• Accessibility is enforced by the compiler, VM, and Core Reflection

• Freedom to adopt modules at your own pace – Modularize the application

– Modularize the libraries

• Some libraries may require more changes to work as modules

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More Information

OpenJDK Project Jigsaw page

http://openjdk.java.net/project/jigsaw

mailto: jigsaw-dev@openjdk.java.net

Module Usage at Compile Time slides http://openjdk.java.net/projects/jigsaw/doc/ModulesAndJavac.pdf

Javadoc for Java Module java APIs:

http://cr.openjdk.java.net/~mr/jigsaw/api/

Modules in the Java Language and VM http://openjdk.java.net/projects/jigsaw/doc/lang-vm.html

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Thank You. Questions?

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