modularity of the java platform javaday (
TRANSCRIPT
Modularity of the Java Platform
Martin Toshev
Who am I
Software engineer @ EPAM Bulgaria
BG JUG governance board member (http://jug.bg)
OpenJDK contributor
Agenda
Modularity 101
Modularity on top of the platform: OSGi
Modularity of the platform: Jigsaw
OSGi and Jigsaw interoperability: Penrose
Modularity 101
Modularity 101
Standard Java libraries are modules - Hibernate, log4j and any library you can basically think of …
Build systems like Maven provide transparent management of modules
Modularity 101
• Benefits of modularization:
– smaller modules are typically tested easier than a monolithic application
– allows for easier evolution of the system - modules evolve independently
Modularity 101
• Benefits of modularization:
– development of the system can be split easier between teams/developers
– increased maintainability of separate modules
Modularity 101
The dependency mechanism used by the JDK introduces a number of problems that modular systems aim to solve:
–The "JAR hell" problem caused by shortcomings of the classloading process
Modularity 101
The dependency mechanism used by the JDK introduces a number of problems that modular systems aim to solve:
–The lack of dynamicity in managing dependent modules
–The lack of loose coupling between modules
Modularity 101
Module systems aim to solve the mentioned problems and typically provide:
• module management• module deployment• versioning• dependency management• module repositories• configuration management
Modularity on top of the platform: OSGi
Modularity on top of the platform: OSGi
OSGi (Open Service Gateway iniatiave) provides a specification for module systems implemented in Java
It is introduced as JSR 8 and JSR 291 to the Java platform
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: An OSGi runtime (module system) makes use of the Java classloading mechanism in order to implement a container for modular units (bundles) and is based on the OSGi spec - a series of standards by the OSGi Alliance. Many application servers are implemented using OSGi as a basis - it is also used in systems from a diversity of areas
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: An OSGi bundle is a just a JAR file that contains source code, bundle metadata and resources. A bundle may provide various services and components to the OSGi runtime. An OSGi runtime allows for bundles to be installed, started, stopped, updated and uninstalled without requiring a reboot
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: The OSGi Core spec defines a layered architecture that determines what is supported by the runtime – each layer defines a particular functionality supported by the runtime and the bundles
OSGi logical units: bundles services services registry life-cycle modules security execution environment
OSGi logical layers:
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: Bundles may export packages for use by other bundles or import packages exported by other bundles - this dependency mechanism is referred to as wire protocol and is provided by the Module layer of OSGi.
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: Bundles may publish services to the runtime and use already published services from the runtime – this dependency mechanism is provided by the Service layer of OSGI.
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: The MANIFEST.MF file of the bundle’s JAR file describes the metadata of the bundle
Manifest-Version: 1.0Bundle-ManifestVersion: 2Bundle-Name: SampleBundle-SymbolicName: com.sampleBundle-Version: 1.0.0.qualifierBundle-Activator: ua.org.javaday.seminar.demo.ActivatorBundle-Vendor: javaday.org.uaRequire-Bundle: org.java.jigsaw.core,org.java.jigsaw.extensionsBundle-RequiredExecutionEnvironment: JavaSE-1.7Service-Component: OSGI-INF/service.xmlImport-Package: ua.org.javaday.seminar.jigsaw.shared;version="1.0.0“Export-Package: ua.org.javaday.seminar.demo.utils
Modularity on top of the platform: OSGi
Q: So what is an OSGi runtime ?A: The runtime may implement extensions based on the OSGi Compendium spec that extends the OSGi Core spec. These could be: remote services
log service
HTTP service
device access service
configuration admin
metatype service
preferences service
user admin
wire admin
DMT admin service
IO connector service
provisioning service
UPnP device service
configuration admin
declarative services
event admin service
deployment admin
XML parser service
monitoring service
others
Modularity on top of the platform: OSGi
• OSGi continues to evolve …
Live DemoModularity on top of the platform: OSGi
Modularity of the platform: Jigsaw
Modularity of the platform: Jigsaw
When speaking of modularity we should also consider the entire runtime (rt.jar) and the JDK core libraries …
… and built-in support for improved "OSGi-like" modules in the Java platform
Modularity of the platform: Jigsaw
The JDK is monolithic …
Modularity of the platform: Jigsaw
• JDK 8 compact profiles provide smaller versions … (javac -profile <profile_name> or make profiles for an OpenJDK build)
compact 1 compact 2 compact 3
Modularity of the platform: Jigsaw
The aim of project Jigsaw is to provide a module system for the Java platform
Although deferred to JDK 9 some additional effort such as Compact Profiles and removed/ deprecated inter-library dependencies have been introduced in JDK8 as an intermediate solution
Modularity of the platform: Jigsaw
Modularization of the Java platform is a significant change that impacts the entire ecosystem - may even break existing projects
Modularity of the platform: Jigsaw
Draft 3 of Jigsaw requirements states that applications using only standard APIs must remain compatible
Draft 3 of Jigsaw requirements also mentions that some JDK-specific APIs must remain compatible but no concrete JDK APIs are listed yet
Modularity of the platform: Jigsaw
Q: So what is exactly project Jigsaw ?
Modularity of the platform: Jigsaw
Q: So what is exactly project Jigsaw ?A: Project Jigsaw provides the basis for JSR 376: Java Platform Module System. Currently work on Jigsaw is being done for:
JEP 200 - define JDK modules (in a modules.xml file in the JDK repo)JEP 201 - reorganize JDK sources into modules and modify JDK buildJEP 220 - restructure JRE/JDK images to accommodate modules
Modularity of the platform: Jigsaw
Q: So what is exactly project Jigsaw ?A: Structure of JDK sources as defined by JEP 201:
oldsrc/{share,$OS}/{classes,native}/$PACKAGE/*.{java,c,h,cpp,hpp}
•newsrc/$MODULE/{share,$OS}/classes/$PACKAGE/*.java
native/include/*.{h,hpp}
$LIBRARY/*.{c,cpp}
conf/*
Modularity of the platform: Jigsaw
Q: So what is exactly project Jigsaw ?A: In the early exploratory phase of project Jigsaw there was a proof-of-concept implementation with JDK8 early-access builds (now dropped).
Modularity of the platform: Jigsaw
Q: So what was exactly the exploratory phase of Jigsaw ?A: Jigsaw POC provided a modularized version of JDK along with additional tools and language support for creating Jigsaw modules. JDK8 early-access builds provided two types of JDK:JDK modules image - all components are preinstalled as
modulesJDK base image + jmod packages - base JDK installation along
with additional Jigsaw modules of the JDK that can be installed on-demand using the jmod tool
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: A collection of Java classes, native libraries and other resources along with metadata that provides name and version of the module and dependencies on other modules
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Jigsaw resolves modules during build and installation.Jigsaw has no dynamics, no module lifecycle. The module system assumes the existence of a foundational module named java.base
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Module can use ("require") other modules and additionally specify version or version ranges for the module dependency - modules are loaded with different module classloaders
module ua.org.javaday.A @ 1.0 { requires ua.org.javaday.B @ [2.0, 3.0);
}
module ua.org.javaday.A { requires ua.org.javaday.B @ >= 1.0; requires ua.org.javaday.C @ < 2.0;}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Module versions are compared using a similar approach as the one used for Debian package versions … The intent is to be able to package a module as an OS-specific package (not applicable for Windows/Mac OS)
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Modules can also "require" optional modules - meaning that compilation succeeds even if the required module is missing
module ua.org.javaday.A { requires optional jdk-corba@8-ea;}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Modules can also "require" local modules - meaning that the local module is a kind of a "mixin" - it is loaded in the same classloader as the requiring module
module ua.org.javaday.A @ 1.0 { requires local ua.org.javaday.B @ [2.0, 3.0);
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: A module may export packages and classes
module ua.org.javaday.A @ 1.0 { requires ua.org.javaday.B @ [2.0, 3.0);exports ua.org.javaday.A.seminar.Sample;exports ua.org.javaday.A.seminar.samples.*;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Modules can explicitly specify which other modules can "require" them
module ua.org.javaday.A @ 2.0 { exports ua.org.javaday.A.seminar;permits ua.org.javaday.B;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Modules can logically provide other module names (aliases):
module ua.org.javaday.A @ 1.0 {provides ua.org.javaday.First @ 2.0;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Modules can have a single entry point
the main() method ua.org.javaday.A.Main is called when invoking:java -m ua.org.javaday.A
module ua.org.javaday.A @ 1.0 {permits ua.org.javaday.B;class ua.org.javaday.A.Main;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: Modules can define multiple views
the main() method ua.org.javaday.A.Main is called when invoking:java -m ua.org.javaday.A
module ua.org.javaday.A {exports ua.org.javaday.A.seminar;view ua.org.javaday.internal.view {
permits ua.org.javaday.B}
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: A module can declare that it provides a service
module ua.org.javaday.A { provides service ua.org.javaday.A.external.TestService with ua.org.javaday.A.external.TestServiceImpl;}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: A module can require a service
module ua.org.javaday.B { requires service ua.org.javaday.A.external.TestService }
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module in terms of the exploratory phase ?A: A service can also be required optionally
module ua.org.javaday.B { requires optional service ua.org.javaday.A.TestService; }
Modularity of the platform: Jigsaw
Q: So why not adopt OSGi (at least the module layer) for modularization of the Java platform ?
Modularity of the platform: Jigsaw
Q: So why not adopt OSGi (at least the module layer) for modularization of the Java platform ?A: As chief architect of the Java platform Mark Reinhold states: The OSGI module layer is not operative at compile time - it addresses modularity only during packaging, deployment and execution. It is also strictly build on top of the platform so it cannot be used to modularize it.
Modularity of the platform: Jigsaw
Q: So why not adopt OSGi (at least the module layer) for modularization of the Java platform ?A: However - according to Peter Kriens (former technical director at the OSGi Alliance and one of the key drivers behind the OSGi spec) Jigsaw is not typically needed an will introduce burden to the platform and modules can be introduced much easier:The only thing we need to add to the existing system is versioning information on the package and record this version in the class file
Live DemoModularity of the platform: Jigsaw
OSGi and Jigsaw interoperability: Penrose
OSGi and Jigsaw interoperability: Penrose
When speaking of JDK modules we should consider interoperability with existing module systems such as OSGi
The purpose of project Penrose is to explore interoperability between OSGi and Jigsaw
OSGi and Jigsaw interoperability: Penrose
Penrose is still in early stage of development …
Current work on project Penrose is deprecated due to the dropped proof-of-concept version of Jigsaw …
OSGi and Jigsaw interoperability: Penrose
Penrose goals:
–ensuring OSGi frameworks run unmodified in a Jigsaw-enabled runtime
–create modules/bundles that have both OSGi and Jigsaw metadata in them
–Jigsaw metadata can be extended with OSGi concepts–extend OSGi to read Jigsaw metadata
OSGi and Jigsaw interoperability: Penrose
Penrose goals:
–mapping Jigsaw metadata to OSGi metadata–resolve Jigsaw modules in an OSGi runtime–enhance OSGi to use Jigsaw APIs–more cross delegation between the two systems …
SummaryQ: Project Jigsaw - when ?
SummaryQ: Project Jigsaw - when ?A: Maybe when the Armagedon comes …
… or maybe in 2016 …
Summary
Q: Projects Jigsaw/Penrose - when ?A: Unless you …… discuss:http://mail.openjdk.java.net/mailman/listinfo/jigsaw-dev… and code:http://hg.openjdk.java.net/jigsaw
Q&A
Thank you
References
OSGi Alliancehttp://www.osgi.org/Main/HomePage
Jigsaw Projecthttp://openjdk.java.net/projects/jigsaw/
Penrose Projecthttp://openjdk.java.net/projects/penrose/
References
Modularity - what is it ?http://www.infoq.com/articles/modular-java-what-is-it/
Java modularity - why ?http://java.dzone.com/articles/java-modularity-2-why
Java JAR hell problemhttp://en.wikipedia.org/wiki/Java_Classloader#JAR_hell
References
Project Jigsaw: Phase Twohttp://mreinhold.org/blog/jigsaw-phase-two
Project Jigsaw: Goals & Requirements Draft 3http://openjdk.java.net/projects/jigsaw/goals-reqs/03
JSR 376: Java Platform Module Systemhttps://www.jcp.org/en/jsr/proposalDetails?id=376
References
Project Jigsaw: Exploratory Phasehttp://
openjdk.java.net/projects/jigsaw/exploratory-phase
References
Java Module System Requirementshttp://openjdk.java.net/projects/jigsaw/doc/draft-java-module-system-requirements-12
Project Jigsaw: The Big Picturehttp://cr.openjdk.java.net/~mr/jigsaw/notes/jigsaw-big-picture-01
Java 8 Modules Jigsaw and OSGihttp://www.slideshare.net/mfrancis/java-8-modules-jigsaw-and-osgi-neil-bartlett
References
Project Jigsaw: Late for the train http://mreinhold.org/blog/late-for-the-train-qa
Unbearable lightness of Jigsaw http://blog.osgi.org/2011/05/unbearable-lightness-of-jigsaw.html
Netbeans discussion on Jigsawhttp://wiki.netbeans.org/Jigsaw
References
Java Modularity - OSGi and Project Jigsawhttp://techdistrict.kirkk.com/2009/06/12/java-modularity-osgi-and-project-jigsaw/
The Modular Java Platform & Project Jigsaw http://www.jfokus.se/jfokus14/preso/Jigsaw.pdf
JAX 2013: A Project Jigsaw primerhttp
://jaxenter.com/a-project-jigsaw-primer-50029.html
References
JavaOne 2013: The Modular Java Platform and Project Jigsaw http://parleys.com/play/52549d02e4b0a43ac12124be/about
OpenJDK Penrose JavaOne 2012http://
www.slideshare.net/bosschaert/open-jdk-penrose-javaone-2012