Introduction

Qwylt is…

  APIs for interacting with modules
    A dependency resolution environment
      SPIs for building module systems
        A platform for module systems to share classes and resources
          APIs for services & dependency injection systems

Qwylt is… a module system framework.

For most Java developers, Qwylt is a set of APIs for interacting with modules: installing them, finding them and loading classes and resources from them—with automatic dependency resolution. It assumes dependency declarations that are versioned and symbolic, eliminating the brittleness of existing 'classpath' solutions. It abstracts the notion of a 'module' such that many implementations are possible, including but not limited to OSGi. It provides a repository model for storing and sharing modules. It abstracts the idea of 'services', enabling easy use of both simple service patterns and dependency injection frameworks.

For applications that require extensibility, Qwylt eliminates the need for custom class loaders, storage and dependency management: a 'plugin' can simply be a module in a repository, easily found, loaded and used.

For diagnostic tools, Qwylt's rich reflective APIs provide a consistent view onto the class loading model, with events providing state change information.

For module system developers, the framework SPIs perform most of the heavy lifting, ensuring a consistent class loading model while leaving the metadata/data formats and storage details to the implementation.

For dependency injection system developers, Qwylt provides APIs, simple integration and an abstract service dependency model: modules can declare dependencies on services as easily as they can on other modules or packages.

For JVM vendors, Qwylt provides a platform for modularizing the JRE libraries, while enabling highly customized storage formats for optimizing performance.

Qwylt is not a module system implementation, and is therefore not a replacement for OSGi or any other existing module system. It is a new environment in which new and existing module systems can be expressed.

Finally, Qwylt supports multiple simultaneous module systems—it is a framework for interconnecting modules, within and across module systems…

Qwylt is… a module system fabric.

Features

Qwylt is composed of API and SPI classes that: The api classes fall in the following layers:

Runtime Module | ClassSpace | ServiceType | ServiceSpace
Discovery ModuleQuery | SearchPolicy | ModuleSystem
Storage ModuleRepository | ModuleArchive
Metadata Export | Import | Version | VersionRange | VersionList
Data ModuleResources

Examples

The following snippet searches a repository for all archives that export a specific package:
ModuleQuery query = ModuleQuery.exportsPackage("com.acme.explosives");
List<ModuleArchive> exporters = repository.findAll(query);
This snippet creates a custom query to search for archives that have errors:
ModuleQuery query = new ModuleQuery() {
    public boolean matches(ModuleArchive archive) {
        return archive.getError() != null;
    }
};
This snippet looks up a service implementation from a given module:
import com.acme.explosives.Explosive;
...
ServiceSpace services = acmeModule.getServiceSpace();
Explosive explosive = services.getService(Explosive.class);
This example shows how to execute the main class of a module specified by name and an optional version expression (e.g. "com.foo" or "com.foo@1.0"):
package util;

import java.lang.module.Module;
import java.lang.module.ModuleArchive;
import java.lang.module.ModuleQuery;
import static java.lang.module.ModuleQuery.*;
import java.lang.module.ModuleRepository;
import static java.lang.module.ModuleRepository.*;
import java.lang.module.ModuleSystem;
import java.lang.reflect.Method;

/**
 * A module launcher.
 */
public class Launcher {

    /**
     * Execute the main class from the selected module.
     *
     * @param moduleReference   The module name and optional version expression.
     * @param arguments         The arguments to the main method.
     * @throws Exception If a failure occurs.
     */
    public static void launch(String moduleReference,
                              String... arguments) throws Exception {

        // Use the root module system to parse the reference...

        ModuleSystem root = ModuleSystem.getRoot();
        ModuleQuery query = root.parseQuery(moduleReference);

        // Use the system repository to look up the archive...

        ModuleRepository repository = getSystemRepository();
        ModuleArchive archive = repository.find(query);
        if (archive == null) {
            throw new Exception(query + " not found.");
        }

        // Get the main class name...

        String mainClassName = archive.getMainClassName();
        if (mainClassName == null) {
            throw new Exception("No main class specified in " + archive);
        }

        // Instantiate the module. If dependencies have not yet
        // been resolved, this will do so or fail...

        Module module = archive.getModule();

        // Instantiate and invoke the main class...

        Class mainClass = module.loadClass(mainClassName);
        Method mainMethod = mainClass.getDeclaredMethod("main", String[].class);
        mainMethod.invoke(null, new Object[]{arguments});
    }
}

Documentation

Download

The current source distribution (v0.8-ea2) is available here.

Build Prerequisites

Installation

  1. Unzip the distribution file.
  2. Download/copy the following test/example dependency jars into the 'lib/' subdirectory. Newer versions of of these jars may be substituted, in which case the "set-external-properties" target in the build.xml file will need to be updated.

Build and Test

Build qwylt.jar, example module system, example modules, tests and run all tests:
    > cd qwylt
    > ant
Remove all build artifacts:
    > ant clean
Build qwylt.jar:
    > ant build
Build and run tests:
    > ant test
Clean, build all and run tests:
    > ant clean test
Generate javadoc:
    > ant doc

Project Structure

    qwylt/
        doc/                    Generated javadoc
        lib/                    Test and example dependency libraries
        src/                    Project sources
            doc/                Document sources
            main/               The framework api and spi sources
            module-systems/     Example module system implementations
                jre.boot-1.0/   A module system representing the JRE
                org.animal-1.0/ A simple properties based module system
                org.zodiac-1.0/ A module system that wraps Equinox
            test/               Test sources
                module-src/     Test modules
                    animal/     Modules in the 'animal' module system format
                    zodiac/     Modules in the OSGi module system format

Acknowledgements

While this project was conceived and created over a very short time, the ideas have been brewing for far longer and have been shaped by many.

This project would not have been possible without the late JSR 277 and the many contributions of its fine expert group members and specification leads. I would particularly like to thank Stanley Ho for his dedicated leadership as well as his patience and thoughtfulness dealing with my suggestions; though the core ideas expressed here derive from my own contributions to 277, many important refinements belong to him. Thanks also to EG members Glyn Normington, Doug Lea, Richard Hall, Michal Cierniak, and Adrian Brock, all excellent collaborators who greatly helped my understanding of the problem domain, and Andy Piper, Daniel Leuck, Gordon Hirsch, Sam Pullara, Hani Suleiman, Brett Porter and Vladimir Strigun for their contributions to 277.

Thanks to Alex Buckley and Mark Reinhold of Sun, John Duimovich of IBM and, especially, my colleague Hal Hildebrand at Oracle for their early feedback, encouragement and willingness to explore possibilities.

Special thanks to Steve Harris, Dhiraj Mutreja and the rest of my management at Oracle; their trust opened many doors.

The banner image started off life as a section from one quilt from an amazing collection created by a very talented artist, Caryl Bryer Fallert; thanks to Caryl for permission to use her images.

Finally, thanks to the OSGi alliance and all who have made it such a huge success; there is no better view than from the shoulders of giants.

Contact

For comments or questions, please contact: bryan.atsatt@oracle.com

Release Notes

Version Date Author Changes
0.8-ea1 27-Jan-2010 Bryan Atsatt Added first cut at services layer.

Renamed java.module to java.lang.module.

0.7-ea2 21-Dec-2009 Bryan Atsatt Refactored Named to AttributeSource, added some accessor methods and AttributeMatcher subclass.

Introduced ScopedName (common scope values) and ExportMatcher subclass (adds version/attribute matchers).

Changed Export to extend ScopedName, and Import to extend ExportMatcher.

Removed ModuleArchive.getAliases(). Now archives must add self as module scoped export, and any aliases can be added in the same way.

0.7-ea1 13-Oct-2009 Bryan Atsatt Enabled covariant returns on methods using collections by switching to bounded wildcards.
0.6 16-Jul-2009 Bryan Atsatt Moved from com.oracle.module to java.module package, and moved query types under spi.

Added ModuleInfo and changed ModuleSystem to support multiple "terms" instead of a single name.

Refactored ClassSpace into ResourceSpace with ClassSpace as subclass.

Added ModuleSystem.validate(ModuleInfo) and ModuleSystem.resolve(ModuleInfo).

Added EventListener.LifeCycle, EventListener.Search and EventDispatcher and wired system to fire events.

Added ModuleArchive.releaseModule() and made newModule() public.

Re-wrote Configuration class to simplify and better define a boostrap process in which the root ModuleSystem is well defined, and each instantiated repository can host additional ModuleSystems.

Collapsed ModuleImport and PackageImport to Export, and PackageExport to Export.

Added java.module.spi.Launcher and ModuleSystem.parseQuery(). Updated example launcher.

Restructured example module systems into separate modules (plain jars for now).

Moved example modules under src/test.

0.5 10-Apr-2009 Bryan Atsatt Removed getClassLoader() from Module to make it possible for a Module instance to span multiple class loaders.

Changed ModuleRepository.getModuleSystem() to return a list to make it possible for one repository to support multiple ModuleSystems.

Updated Module and ModuleArchive to implement AnnotatedElement.

Updated AnimalRepository to support annotations and added test case.

0.4 21-Mar-2009 Bryan Atsatt Added example module system wrapping Equinox ('zodiac').
0.3 14-Mar-2009 Bryan Atsatt Refactored ExportedPackage into a base Export type and PackageExport.
0.2 13-Mar-2009 Bryan Atsatt Moved RootRepository and root class space instantiation to Configuration.
0.1 20-Feb-2009 Bryan Atsatt Initial release.

Project License

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