Post on 10-May-2015
description
Modularity of the Java Platform
Martin Toshev
BG JUG mailing list:https://groups.google.com/forum/#!forum/bg-jug
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 initiave) 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. 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: sample.ActivatorBundle-Vendor: QIVICONRequire-Bundle: org.eclipse.smarthome.core, com.qivicon.extensionsBundle-RequiredExecutionEnvironment: JavaSE-1.7Service-Component: OSGI-INF/service.xmlImport-Package: com.qivicon.services.hdm;version="3.0.0“Export-Package: com.sample.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
Q: What about Maven support for OSGi bundles ?
Modularity on top of the platform: OSGi
Q: What about Maven support for OSGi bundles ?A: Such a support is provided by the Tycho Maven plug-ins that provide support for packaging types, target platform definitions, interoperability with the Maven dependency mechanism and so on …
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
Q: So what is exactly project Jigsaw ?
Modularity of the platform: Jigsaw
Q: So what is exactly project Jigsaw ?A: Jigsaw will provide the basis for a Java Module System JSR
Modularity of the platform: Jigsaw
Q: So what is exactly project Jigsaw ?A: Project Jigsaw provides a modularized version of JDK along with additional tools and language support for creating Jigsaw modules. Currently early-access builds provide two types of JDK: JDK modules image - all components are preinstalled as
modules JDK 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: So what is exactly project Jigsaw ?A: No jre directory exists anymore in the JDK installation, rt.jar and tools.jar no longer exist. Modular JDK must be compatible with existing applications to a greater extend. Legacy applications are expected to run on a Jigsaw JDK if:
– they don't depend upon the internal structure of the JDK/JRE
– they use only supported APIs
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 ?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 org.bgjug.A @ 1.0 { requires org.bgjug.B @ [2.0, 3.0);
}
module org.bgjug.A { requires org.bgjug.B @ >= 1.0; requires org.bgjug.C @ < 2.0;}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Module versions are compared using a similar approach as the one used for Debian package versions …
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Modules can also "require" optional modules - meaning that compilation succeeds even if the required module is missing
module org.bgjug.A { requires optional jdk-corba@8-ea;}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?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 org.bgjug.A @ 1.0 { requires local org.bgjug.B @ [2.0,
3.0);}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: A module may export packages and classes
module org.bgjug.A @ 1.0 { requires org.bgjug.B @ [2.0, 3.0);exports org.bgjug.A.seminar.Sample;exports org.bgjug.A.seminar.samples.*;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Modules can explicitly specify which other modules can "require" them
module org.bgjug.A @ 2.0 { exports org.bgjug.A.seminar;permits org.bgjug.B;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Modules can logically provide other module names (aliases):
module com.bgjug.A @ 1.0 {provides com.bgjug.First @ 2.0;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Modules can have a single entry point
the main() method org.bgjug.A.Main is called when invoking:java -m org.bgjug.A
module org.bgjug.A @ 1.0 {permits org.bgjug.B;class org.bgjug.A.Main;
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: Modules can define multiple views
the main() method org.bgjug.A.Main is called when invoking:java -m org.bgjug.A
module org.bgjug.A {exports org.bgjug.A.seminar;view org.bgjug.internal.view {
permits org.bgjug.B}
}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: A module can declare that it provides a service
module org.bgjug.A { provides service org.bgjug.A.external.TestService with org.bgjug.A.external.TestServiceImpl;}
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: A module can require a service
module org.bgjug.B { requires service org.bgjug.A.external.TestService }
Modularity of the platform: Jigsaw
Q: What is a Jigsaw module ?A: A service can also be required optionally
module org.bgjug.B{ requires optional service org.bgjug.A.TestService;}
Modularity of the platform: Jigsaw
Q: How are modules compiled ?
Modularity of the platform: Jigsaw
Q: How are modules compiled ?A: The javac compiler is extended with a ModulePath - the equivalent of ClassPath but for module dependencies(-modulepath option)For javac the -d option (that specifies the output directory):
– outputs to legacy single-module structure if ClassPath is set
– outputs to multi-module structure if ModulePath is set
Modularity of the platform: Jigsaw
Q: How are modules managed ?
Modularity of the platform: Jigsaw
Q: How are modules managed ?A: Modules can be added to module libraries. Various tools are added to support creation of modules, module libraries and module repositories and packaging of artifacts:
– jmod - for managing modules and module libraries– jpkg - for packaging modules (uses pack200 compression)
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.For compile-time resolution of OSGi dependencies during development IDEs (such as Eclipse) and build tooling (such as Maven) provide a mechanism for specifying a target platform which is collection of bundles used to provide compile-time dependencies
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
Modularity of the platform: Jigsaw
Q: What about IDE support for Jigsaw module development ?
Modularity of the platform: Jigsaw
Q: What about IDE support for Jigsaw module development ?A: It is still an early stage to consider possible IDE support - IDE vendors outline use cases for Jigsaw usage in order to consider how to extend their IDEs with Jigsaw support (valid mostly for NetBeans - Eclipse and IntelliJ are still idle).However - according to Peter Kriens the structure of a JDK module (especially the module-info.java file) will increase effort needed to support modules in the various IDEs and build tools
Modularity of the platform: Jigsaw
Q: What about Maven support for Jigsaw module development ?
Modularity of the platform: Jigsaw
Q: What about Maven support for Jigsaw module development ?A: Still at a very early stage of discussion - but most probably Maven will provide build-in support for Jigsaw modules and module dependency resolution from upstream Jigsaw repositories
Modularity of the platform: Jigsaw
Q: What about Maven support for Jigsaw module development ?A: According the Peter Kriens:And not to forget the build tools, they will start having to interpret the module-info file and link to the appropriate module system to find their class path. Today, a build tool tells the compiler its class path, in the future it would first have to compile or interpret the Java file. This alone will probably kill 90% of the ant scripts because the class path is used in other places then compiling. Also maven will have to start to interact with this
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 …
OSGi and Jigsaw interoperability: Penrose
• Penrose goals:
– ensuring OSGi frameworks run unmodified in an 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 module info
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 repositories and APIs– more cross delegation between the two systems …
OSGi and Jigsaw interoperability: Penrose
• Since module-info.java is compiled to module-info.class this implies that class file must be parsed in order to read metadata
• Penrose proposes a simpler JSON format (module-info.json) that can be used to generate both Jigsaw and OSGi metadata
OSGi and Jigsaw interoperability: Penrose
MANIFEST.MF (OSGi)
module-info.java (Jigsaw)
module org.bgjug @ 1.0 {exports org.bgjug.external;
}
Manifest-Version: 1.0Bundle-ManifestVersion: 2Bundle-Name: org.bgjugBundle-SymbolicName: org.bgjugBundle-RequiredExecutionEnvironment: JavaSE-1.7Export-Package: org.bgjug.external;version="1.0.0"
module-info.json (Penrose)"module" : { "name" : "org.bgjug", "version": 1.0, "exports" : [{
"name" : "org.bgjug.external", "org.osgi.version" :
"1.0.0" }]
}
module-info.json (Penrose)
Summary
Q: Projects Jigsaw/Penrose - when ?
Summary
Q: Projects Jigsaw/Penrose - when ?A: Maybe when the Armagedon comes …
Summary
Q: Projects Jigsaw/Penrose - when ?A: Unless you …… discuss:http://mail.openjdk.java.net/mailman/listinfo/penrose-devhttp://mail.openjdk.java.net/mailman/listinfo/jigsaw-devhttp://mail.openjdk.java.net/mailman/listinfo/penrose-discuss… and code:http://hg.openjdk.java.net/jigsawhttp://hg.openjdk.java.net/penrose
Q&A
Thank you
Bulgarian JUG mailing list:https://groups.google.com/forum/#!forum/bg-jug
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
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