1.0.3
service
element attributefilter
attributebean-name
attributecardinality
attributereference
element attributesreference
and OSGi Service DynamicsBundleContext
Application development has seen significant changes in the last years, moving towards a simpler, more agile, POJO-based programming model in order to keep a fast pace. Dependency injection and Aspect Oriented Programming, which were once bleeding edge ideas, are used on a daily basis by most developers to manage and simplify the complexity of their applications.
However, in terms of deployment, things have remained mainly unchanged. Even though code bases are divided into modules, whether logical, conceptual or physical, at runtime they are seen as one monolithic application in which, making a change (be it large or small), requires a restart. OSGi aims to change this by allowing applications to be divided into modules that can have different life cycles, dependencies and still exist as a whole.
Spring Dynamic Modules focuses on integrating Spring Framework powerful, non-invasive programming model and concepts with the dynamics and modularity of OSGi platform. It allows transparent exporting and importing of OSGi services, life cycle management and control.
While every effort has been made to ensure that this documentation is comprehensive and there are no errors, nevertheless some topics might require more explanation and some typos might have crept in. If you do spot any mistakes or even more serious errors and you can spare a few cycles during lunch, please do bring the error to the attention of the Spring Dynamic Modules team by raising an issue. Thank you.
This document is the reference guide for Spring Dynamic Modules. It defines Spring Dynamic Modules concepts and semantics, the syntax for the OSGi Service Platform based namespaces, the Dynamic Modules extender bundle and the OSGi manifest header entries defined by Dynamic Modules. For a tutorial introduction to building OSGi-based applications with Spring Dynamic Modules see our online page.
OSGi developers looking for an introduction to Spring should review the introductory articles on the springframework.org site.
Note: OSGi is a trademark of the OSGi Alliance. Project name is pending final approval from the Alliance.
Note: Please see the known issues page for Spring Dynamic Modules release.
The Spring Framework is the leading full-stack Java/JEE application framework. It provides a lightweight container and a non-invasive programming model enabled by the use of dependency injection, AOP, and portable service abstractions. The OSGi Service Platform offers a dynamic application execution environment in which modules (bundles) can be installed, updated, or removed on the fly. It also has excellent support for modularity and versioning.
Spring Dynamic Modules makes it easy to write Spring applications that can be deployed in an OSGi execution environment, and that can take advantage of the services offered by the OSGi framework. Spring's OSGi support also makes development of OSGi applications simpler and more productive by building on the ease-of-use and power of the Spring Framework. For enterprise applications, the combination of Spring Dynamic Modules and the OSGi platform provides:
Better separation of application logic into modules, with runtime enforcement of module boundaries
The ability to deploy multiple versions of a module (or library) concurrently
The ability to dynamically discover and use services provided by other modules in the system
The ability to dynamically install, update and uninstall modules in a running system
Use of the Spring Framework to instantiate, configure, assemble, and decorate components within and across modules.
A simple and familiar programming model for enterprise developers to exploit the features of the OSGi platform.
We believe that the combination of OSGi and Spring offers a comprehensive model for building enterprise applications.
Spring Dynamic Modules 1.0 supports JDK level 1.4 and above
and OSGi
R4 and above. Bundles deployed for
use with Spring Dynamic Modules should specify
"Bundle-ManifestVersion: 2"
in their manifest (OSGi R4).
We test against Equinox 3.2.2, Felix 1.0.1, and Knopflerfish 2.0.3 as part of our
continuous integration process.
This part of the reference documentation explains the core functionality offered by Spring Dynamic Modules.
Chapter 3, Bundles and Application Contexts describes the relationship between an OSGi Bundle and a Spring Application Context, and introduces the Spring Extender Bundle support for instantiating application contexts automatically.
Chapter 4, Packaging and Deploying Spring-based OSGi applications describes how to deploy the Spring Framework jar files in an OSGi environment, and how to reference external APIs from your application bundles should you need to do so. This chapter also explains some of the issues to be aware of when using existing enterprise libraries not designed for OSGi in an OSGi environment.
Chapter 5, The Service Registry describes how to export Spring beans as services in the OSGi service registry, and how to inject references to OSGi services into beans. This chapter also defines how the dynamic life-cycle of OSGi services and bundles is supported.
Chapter 6, Working with Bundles describes how to declare a bean that represents an OSGi bundle, including support for installing new bundles into the OSGi platform.
Chapter 7, Testing OSGi based Applications explains the integration testing support provided by Spring Dynamic Modules. This support enables you to write simple JUnit integration tests that can start up an OSGi environment, install the bundles needed for the integration test, execute the test case(s) inside of OSGi, and return the results to the runner. This makes it easy to integrate OSGi integration testing into any environment that can work with JUnit.
The unit of deployment (and modularity) in OSGi is the bundle (see section 3.2 of the OSGi Service Platform Core Specification). A bundle known to the OSGi runtime is in one of three steady states: installed, resolved, or active. Bundles may export services (objects) to the OSGi service registry, and by so doing make these services available for other bundles to discover and to use. Bundles may also export Java packages, enabling other bundles to import the exported types.
In Spring the primary unit of modularity is an application context, which contains some number of beans (objects managed by the Spring application context). Application contexts can be configured in a hierarchy such that a child application context can see beans defined in a parent, but not vice-versa. The Spring concepts of exporters and factory beans are used to export references to beans to clients outside of the application context, and to inject references to services that are defined outside of the application context.
There is a natural affinity between an OSGi bundle and a Spring application context. Using Spring Dynamic Modules, an active bundle may contain a Spring application context, responsible for the instantiation, configuration, assembly, and decoration of the objects (beans) within the bundle. Some of these beans may optionally be exported as OSGi services and thus made available to other bundles, beans within the bundle may also be transparently injected with references to OSGi services.
Spring Dynamic Modules provides an OSGi bundle
org.springframework.bundle.osgi.extender
. This
bundle is responsible for instantiating the Spring application contexts
for your application bundles. It serves the same purpose as the ContextLoaderListener
does for Spring web applications. Once the extender bundle is installed
and started it looks for any existing Spring-powered bundles that are
already in the ACTIVE state and creates application contexts on their
behalf. In addition, it listens for bundle starting events and
automatically creates an application context for any Spring-powered
bundle that is subsequently started. Section 4.1, “Bundle format and Manifest headers”
describes what the extender recognizes as a "Spring-powered bundle".
The extender bundle creates applications contexts asynchronously. This behaviour ensures that starting an OSGi Service Platform is fast and that bundles with service inter-dependencies do not cause deadlock on startup. A Spring-powered bundle may therefore transition to the STARTED state before its application context has been created. It is possible to force synchronous creation of application contexts on a bundle-by-bundle basis. See Section 4.1, “Bundle format and Manifest headers” for information on how to specify this behaviour.
If application context creation fails for any reason then the failure cause is logged. The bundle remains in the STARTED state. There will be no services exported to the registry from the application context in this scenario.
If an application context declares mandatory dependencies on the availability of certain OSGi services (see Chapter 5, The Service Registry) then creation of the application context is blocked until all mandatory dependencies can be satisfied through matching services available in the OSGi service registry. Since a service may come and go at any moment in an OSGi environment, this behaviour only guarantees that all mandatory services were available at the moment creation of the application context began. One or more services may subsequently become unavailable again during the process of application context creation. Chapter 5, The Service Registry describes what happens when a mandatory service reference becomes unsatisfied. In practice, for most enterprise applications built using Spring Dynamic Modules services, the set of available services and bundles will reach a steady state once the platform and its installed bundles are all started. In such a world the behaviour of waiting for mandatory dependencies simply ensures that bundles A and B, where bundle A depends on services exported by bundle B, may be started in any order.
A timeout applies to the wait for mandatory dependencies to be
satisfied. By default the timeout is set to 5 minutes, but this value
can be configured using the timeout
directive. See
Section 4.1, “Bundle format and Manifest headers” for details.
It is possible to change the application context creation semantics so that application context creation fails if all mandatory services are not immediately available upon startup (see section 4.1). When configured to not wait for dependencies, a bundle with unsatisfied mandatory dependencies will be stopped, leaving the bundle in the RESOLVED state.
Once the application context creation for a bundle has
completed, the application context object is automatically exported as
a service available through the OSGi Service Registry. The context is
published under the interface
org.springframework.context.ApplicationContext
(and
also all of the visible super-interfaces and types implemented by the
context). The published service has a service property named
org.springframework.context.service.name
whose
value is set to the bundle symbolic name of the bundle hosting the
application context. It is possible to prevent publication of the
application context as a service using a directive in the bundle's
manifest. See Section 4.1, “Bundle format and Manifest headers” for details.
Note: the application context is published as a service
primarily to facilitate testing, administration, and management.
Accessing this context object at runtime and invoking
getBean()
or similar operations is discouraged. The
preferred way to access a bean defined in another application context
is to export that bean as an OSGi service from the defining context,
and then to import a reference to that service in the context that
needs access to the service. Going via the service registry in this
way ensures that a bean only sees services with compatible versions of
service types, and that OSGi platform dynamics are respected.
OSGi is a dynamic platform: bundles may be installed, started, updated, stopped, and uninstalled at any time during the running of the framework.
When an active bundle is stopped, any services it exported during its lifetime are automatically unregistered and the bundle returns to the resolved state. A stopped bundle should release any resources it has acquired and terminate any threads. Packages exported by a stopped bundle continue to be available to other bundles.
A bundle in the resolved state may be uninstalled: packages that were exported by an uninstalled bundle continue to be available to bundles that imported them (but not to newly installed bundles).
A bundle in the resolved state may also be updated. The update process migrates from one version of a bundle to another version of the same bundle.
Finally of course, a resolved bundle can be started, which transitions it to the active state.
The OSGi PackageAdmin
refreshPackages
operation refreshes packages across
the whole OSGi framework or a given subset of installed bundles. During
the refresh, an application context in an affected bundle will be
stopped and restarted. After a refreshPackages
operation, packages exported by older versions of updated bundles, or
packages exported by uninstalled bundles, are no longer available.
Consult the OSGi specifications for full details.
When a Spring-powered bundle is stopped, the application context
created for it is automatically destroyed. All services exported by the
bundle will be unregistered (removed from the service registry) and the
normal application context tear-down life-cycle is observed
(org.springframework.beans.factory.DisposableBean
implementors
and destroy-method
callbacks are invoked on beans in the context).
If a Spring-powered bundle that has been stopped is subsequently re-started, a new application context will be created for it.
The Spring Framework defines a resource abstraction for loading
resources within an application context (see Spring's
resource abstraction). All resource loading is done through the
org.springframework.core.io.ResourceLoader
associated with the application
context. The org.springframework.core.io.ResourceLoader
is also
available to beans wishing to load resources programmatically. Resource paths with
explicit prefixes - for example "classpath:" are treated uniformly
across all application context types (for example, web application
contexts and classpath-based application contexts). Relative resource
paths are interpreted differently based on the kind of application
context being created. This enables easy integration testing outside
the ultimate deployment environment.
OSGi 4.0.x specification defines three different spaces from which a resource can be loaded. Spring-DM supports all of them through its dedicated OSGi-specific application context and dedicated prefixes:
Table 3.1. OSGi resource search strategies
OSGi search strategy | prefix | Explanation |
---|---|---|
Class Space | classpath: | Search the bundle classloader (the bundle and all imported packages). Forces the bundle to be resolved. |
JAR File (or JarSpace) | osgibundlejar: | Search only the bundle jar. Provides low-level access without requiring the bundle to be resolved. |
Bundle Space | osgibundle: | Search the bundle jar and its attached fragments (if there are any). Will never create a class loader or resolve the bundle. |
Please consult section 4.3.12 of the OSGi specification for an in depth explanation of the differences between them.
Note that if no prefix is specified, the bundle space will be used.
All of the regular Spring resource prefixes such as file:
and
http:
are also supported, as are the pattern matching wildcards.
Resources loaded using such prefixes may come from any location, they
are not restricted to being defined within the resource-loading bundle
or its attached fragments.
OSGi platforms may define their own unique prefixes for accessing
bundle contents. For example, Equinox defines the bundleresource:
and
bundlentry:
prefixes). These platform specific prefixes may also be
used with Spring OSGi, at the cost of course of tying yourself to a
particular OSGi implementation.
In general there is no need to depend on any OSGi APIs when using
the Spring Dynamic Modules support. If you do need
access to the OSGi BundleContext
object for your
bundle, then Spring makes this easy to do.
The OSGi application context created by the Spring extender will
automatically contain a bean of type BundleContext
and with name bundleContext
. You can inject a
reference to this bean into any bean in the application context either
by-name or by-type. In addition, Spring Dynamic Modules defines the
interface
org.springframework.osgi.context.BundleContextAware
:
public interface BundleContextAware { public void setBundleContext(BundleContext context); }
Any bean implementing this interface will be injected with a
reference to the bundle context when it is configured by Spring. If you
wish to use this facility within a bundle, remember to import the
package org.springframework.osgi.context
in your
bundle manifest.
The application context is bound to the bundle in which it lives. Thus, if the declaring bundle is being shutdown, the application context will be destroyed as well, all exported services being unregistered and all service imported dispose of.
Note however that a bundle can be closed individually or as part of a bigger event such as shutting down the entire OSGi platform. In this case or when the extender bundle is being closed down, the managed application contexts will be closed in a managed manner based on the service dependencies between them. Please see the next section for more details.
If the extender bundle is stopped, then all the application contexts created by the extender will be destroyed. Application contexts are shutdown in the following order:
Application contexts that do not export any services, or that export services that are not currently referenced, are shutdown in reverse order of bundle id. (Most recently installed bundles have their application contexts shutdown first).
Shutting down the application contexts in step (1) may have released references these contexts were holding such that there are now additional application contexts that can be shutdown. If so, repeat step 1 again.
If there are no more active application contexts, we have finished. If there are active application contexts then there must be a cyclic dependency of references. The circle is broken by determining the highest ranking service exported by each context: the bundle with the lowest ranking service in this set (or in the event of a tie, the highest service id), is shut down. Repeat from step (1).
A traditional Spring application uses either a single application context, or a parent context containing service layer, data layer, and domain objects with a child context containing web layer components. The application context may well be formed by aggregating the contents of multiple configuration files.
When deploying an application to OSGi the more natural structure is to package the application as a set of peer bundles (application contexts) interacting via the OSGi service registry. Independent subsystems should be packaged as independent bundles or sets of bundles (vertical partitioning). A subsystem may be package in a single bundle, or divided into several bundles partitioned by layer (horizontal partitioning). A straightforward web application may for example be divided into four modules (bundles): a web bundle, service layer bundle, data layer bundle, and domain model bundle. Such an application would look like this:
In this example the data layer bundle yields a data layer application context that contains a number of internal components (beans). Two of those beans are made publicly available outside of the application context by publishing them as services in the OSGi service registry.
The service layer bundle yields a service layer application context that contains a number of internal components (beans). Some of those components depend on data layer services, and import those services from the OSGi service registry. Two of the service layer components are made externally available as services in the OSGi service registry.
The web component bundle yields a web application context that contains a number of internal components (beans). Some of those components depend on application services, and import those services from the OSGi service registry. Since the domain model bundle contributes only domain model types, but does not need to create any components of its own, it has no associated application context.
Each application module should be packaged as an OSGi bundle. A
bundle is essentially a jar file with a
META-INF/MANIFEST.MF
file containing a series of
headers recognized by the OSGi Service Platform. See the OSGi Service
Platform Core Specification section 3.2 for details. Some OSGi
implementations may support exploded jar files, but the format remains
the same.
The Spring extender recognizes a bundle as "Spring-powered" and will create an associated application context when the bundle is started and one or both of the following conditions is true:
The bundle path contains a folder
META-INF/spring
with one or more files in that
folder with a '.xml' extension.
META-INF/MANIFEST.MF
contains a manifest
header Spring-Context
.
In addition, if the optional
SpringExtender-Version
header is declared in the
bundle manifest, then the extender will only recognize bundles where the
specified version constraints are satisfied by the version of the
extender bundle (Bundle-Version
). The value of the
SpringExtender-Version
header must follow the syntax
for a version range as specified in section 3.2.5 of the OSGi Service
Platform Core Specification.
In the absence of the Spring-Context
header the
extender expects every ".xml" file in the
META-INF/spring
folder to be a valid Spring
configuration file, and all directives (see below) take on their default
values.
An application context is constructed from this set of files. A suggested practice is to split the application context configuration into at least two files, named by convention modulename-context.xml and modulename-osgi-context.xml. The modulename-context.xml file contains regular bean definitions independent of any knowledge of OSGi. The modulename-osgi-context.xml file contains the bean definitions for importing and exporting OSGi services. It may (but is not required to) use the Spring Dynamic Modules OSGi schema as the top-level namespace instead of the Spring 'beans' namespace.
The Spring-Context
manifest header may be used
to specify an alternate set of configuration files. The resource paths
are treated as relative resource paths and resolve to entries defined in
the bundle and the set of attached fragments. When the
Spring-Context
header defines at least one
configuration file location, any files in
META-INF/spring
are ignored unless directly
referenced from the Spring-Context
header.
The syntax for the Spring-Context
header value
is:
Spring-Context-Value ::= context ( ',' context ) * context ::= path ( ';' path ) * (';' directive) *
This syntax is consistent with the OSGi Service Platform common header syntax defined in section 3.2.3 of the OSGi Service Platform Core Specification.
For example, the manifest entry:
Spring-Context: config/account-data-context.xml, config/account-security-context.xml
will cause an application context to be instantiated using the
configuration found in the files
account-data-context.xml
and
account-security-context.xml
in the bundle jar
file.
A number of directives are available for use with the
Spring-Context
header. These directives are:
create-asynchronously (false|true): controls whether the application context is created asynchronously (the default), or synchronously.
For example:
Spring-Context: *;create-asynchronously:=false
Creates an application context synchronously, using all of the
"*.xml" files contained in the META-INF/spring
folder.
Spring-Context: config/account-data-context.xml;create-asynchrously:=false
Creates an application context synchronously using the
config/account-data-context.xml
configuration file.
Care must be taken when specifying synchronous context creation as the
application context will be created on the OSGi event thread, blocking
further event delivery until the context is fully initialized. If an
error occurs during the synchronous creation of the application context
then a FrameworkEvent.ERROR
event is raised. The bundle will still
proceed to the ACTIVE
state.
wait-for-dependencies (true|false): controls whether or not application context creation should wait for any mandatory service dependencies to be satisfied before proceeding (the default), or proceed immediately without waiting if dependencies are not satisfied upon startup.
For example:
Spring-Context: config/osgi-*.xml;wait-for-dependencies:=false
Creates an application context using all the files matching "osgi-*.xml" in the config directory. Context creation will begin immediately even if dependencies are not satisfied. This essentially means that mandatory service references are treated as though they were optional - clients will be injected with a service object that may not be backed by an actual service in the registry initially. See section 5.2 for more details.
timeout (300): the time to wait (in
seconds) for mandatory dependencies to be satisfied before giving up
and failing application context creation. This setting is ignored if
wait-for-dependencies:=false
is specified. The
default is 5 minutes (300 seconds).
For example:
Spring-Context: *;timeout:=60
Creates an application context that waits up to 1 minute (60 seconds) for its mandatory dependencies to appear.
publish-context (true|false): controls whether or not the application context object itself should be published in the OSGi service registry. The default is to publish the context.
For example:
Spring-Context: *;publish-context:=false
If there is no Spring-Context manifest entry, or no value is specified for a given directive in that entry, then the directive takes on its default value.
The Spring Dynamic Modules project provides an number of bundle artifacts that must be installed in your OSGi platform in order for the Spring extender to function correctly:
The extender bundle itself,
org.springframework.osgi.extender
The core implementation bundle for the Spring Dynamic Modules
support, org.springframework.osgi.core
The Spring Dynamic Modules I/O support library bundle,
org.springframework.osgi.io
In addition the Spring Framework provides a number of bundles that are required to be installed. As of release 2.5 of the Spring Framework, the Spring jars included in the Spring distribution are valid OSGi bundles and can be installed directly into an OSGi platform. The minimum required set of bundles is:
spring-core.jar (bundle symbolic name
org.springframework.bundle.spring.core
)
spring-context.jar (bundle symbolic name
org.springframework.bundle.spring.context
)
spring-beans.jar (bundle symbolic name
org.springframework.bundle.spring.beans
)
spring-aop.jar (bundle symbolic name
org.springframework.bundle.spring.aop
)
In additional the following supporting library bundles are required. OSGi-ready versions of these libraries are shipped with the Spring Dynamic Modules distribution.
aopalliance
backport-util (when running on JDK 1.4)
cglib-nodep (when proxying classes rather then interfaces, needed in most cases)
commons-logging API (SLF4J version highly recommended)
logging implementation such as log4j
Spring 2.0 introduced (among other things) easier XML configuration and extensible XML authoring. The latter gives the ability of creating custom schemas that are discovered automatically (in non-OSGi environment) by the Spring XML infrastructure by including them in the classpath. Spring-DM is aware of this process and supports it in OSGi environments so that custom schemas are available to bundles that use them without any extra code or manifest declaration.
All bundles deployed in the OSGi space (whether they are Spring-powered
or not) are scanned by Spring-DM for
custom Spring namespace declaration (by checking the bundle space forMETA-INF/spring.handlers
and
META-INF/spring.schemas
). If these are found, Spring-DM will make the schemas and the namespaces available through an OSGi
service that will be automatically used by Spring-powered bundles. This mean that if you deploy a bundle that uses a custom schema, all you have to do
is deploy the library that provides the namespace parser and the schema.
Bundles that embedded inside their classpath libraries that provide custom schemas will use these over those available in the OSGi space. However,
the namespaces of the embedded libraries will not shared with other bundles, that is, they will not be seen by any other bundle.
In short, with using Spring-DM, custom Spring namespaces are supported transparently without any additional work. Embedded namespace providers will have priority but will not be shared, as opposed to providers deployed as bundles which will be seen (and used) by others.
Refer to the OSGi Service Platform for details of the
Import-Package
and Export-Package
manifest headers. Your bundle will need an
Import-Package
entry for every external package that
the bundle depends on. If your bundle provides types that other bundles
need access to, you will need Export-Package
entries
for every package that should be available from outside of the
bundle.
Many enterprise application libraries assume that all of the types and resources that comprise the application are accessible through the context class loader. While most developers do not use the context class loader, the loader is used heavily by application servers, containers or applications that are multi-threaded.
In OSGi R4, the set of types and resources available through the context class loader is undefined. This means that the OSGi platform does not make a guarantee of the thread context class loader value or in other words, it does not manage it.
Thus code (for example libraries) that performs manual class loading or that generates new classes dynamically can cause problems when executed inside an OSGi environment.
Spring Dynamic Modules guarantees that during the creation of an application context on behalf of a given bundle, all of the types and resources on the bundle's classpath are accessible via the context class loader. Spring Dynamic Modules also allows you to control what is accessible through the context class loader when invoking external services and when servicing requests on exported services. See section 5 for details on this.
Work is underway in the OSGi R5 timeframe to provide standardized
support for dealing with generated classes and implicit class path
dependencies introduced by third-party libraries. In the interim you may
need to rely on workarounds such as the
DynamicImport-Package
manifest header, or the
facilities provided by specific OSGi implementations such as Equinox's
buddy mechanism. The Spring Dynamic Modules documentation contains more
details on known issues with common enterprise libraries and the
workarounds.
Your chosen OSGi platform implementation should be able to provide
you with a good deal of information about the current status of the OSGi
environment. For example, starting Equinox with the
-console
argument provides a command-line console
through which you can determine which bundles are installed and their
states, the packages and services exported by bundles, find out why a
bundle has failed to resolve, and drive bundles through the
lifecycle.
In addition, Spring itself and the Spring Dynamic Modules bundles
contain extensive logging instrumentation that can help you diagnose
problems. The recommended approach is to deploy the Simple Logging
Facade for Java (slf4j)
slf4j-api.jar and slf4j-log4j13.jar bundles (the jar files distributed
by the project are valid OSGi bundles). Then you simply need to create a
log4j.properties
file in the root of your bundle
classpath.
Note that Spring Dynamic Modules uses commons-logging API internally which means that its logging implementation is fully pluggable. Please see the FAQ and Resources pages for more information on other logging libraries besides log4j.
The OSGi service registry enables a bundle to publish objects to a shared registry, advertised via a given set of Java interfaces. Published services also have service properties associated with them in the registry.
Spring Dynamic Modules provides an osgi
namespace for Spring (see
Appendix F, Spring Dynamic Modules Schema) that can be used to export
Spring beans as OSGi services, and
to define references to services obtained via the service registry. The
namespace elements may be used nested inside another top-level namespace
(typically the Spring beans
namespace), or within the top-level
osgi
element.
The following example shows the use of the osgi
namespace within the familiar Spring beans element:
<?xml version="1.0" encoding="UTF-8"?>; <beans xmlns="http://www.springframework.org/schema/beans" (1) xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:osgi="http://www.springframework.org/schema/osgi" (2) xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd (3) http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi.xsd"> <osgi:service id="simpleServiceOsgi" ref="simpleService" (4) interface="org.xyz.MyService" /> </beans>
(1) | Use Spring Framework |
(2) | Import Spring Dynamic Modules schema and associate a prefix with its namespace ( |
(3) | Make sure to import Spring beans schema version 2.5. |
(4) | Use Spring Dynamic Modules elements using the declared namespace prefix (in this example |
Using the OSGi namespace as a top-level namespace, the same service would be declared as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans:beans (1) xmlns="http://www.springframework.org/schema/osgi" (2) xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans" (3) xsi:schemaLocation="http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> (4) <service id="simpleServiceOsgi" ref="simpleService" (5) interface="org.xyz.MyService" /> </beans:beans> (1)
(1) |
|
(2) | Use Spring Dynamic Modules schema as the default namespace. |
(3) | Import Spring Framework |
(4) | Make sure to import Spring beans schema version 2.5. |
(5) | Use Spring Dynamic Modules elements without any prefix. |
Using the OSGi namespace as a top-level namespace is particularly convenient when following the recommendation of Section 4.1, “Bundle format and Manifest headers” to use a dedicated configuration file for all OSGi-related declarations.
The service
element is used to define a bean
representing an exported OSGi service. At a minimum you must specify the
bean to be exported, and the service interface that
the service advertises.
For example, the declaration
<service ref="beanToPublish" interface="com.xyz.MessageService"/>
exports the bean with name beanToPublish
with
interface com.xyz.MessageService
. The published
service will have a service property with the name
org.springframework.osgi.bean.name
set to the name of
the target bean being registered (beanToPublish
in
this case).
The bean defined by the
service
element is of type
org.osgi.framework.ServiceRegistration
and is the
ServiceRegistration
object resulting from registering
the exported bean with the OSGi service registry. By giving this bean an
id you can inject a reference to the
ServiceRegistration
object into other beans if
needed. For example:
<service id="myServiceRegistration" ref="beanToPublish" interface="com.xyz.MessageService"/>
As an alternative to exporting a named bean, the bean to be
exported to the service registry may be defined as an anonymous inner
bean of the service element. Typically the top-level namespace would be
the beans
namespace when using this style:
<osgi:service interface="com.xyz.MessageService"> <bean class="SomeClass"> ... </bean> </osgi:service>
If the bean to be exported implements the
org.osgi.framework.ServiceFactory
interface then the
ServiceFactory
contract is honored as per section 5.6
of the OSGi Service Platform Core Specification. As an alternative to
implementing this OSGi API, Spring Dynamic Modules introduces a new bean
scope, the bundle
scope. When a bean with bundle
scope is exported as an OSGi service then one instance of the bean will
be created for each unique client (service importer) bundle that
obtains a reference to it through the OSGi service registry. When a
service importing bundle is stopped, the bean instance associated with
it is disposed. To declare a bean with bundle
scope
simply use the scope
attribute of the
bean
element:
<osgi:service ref="beanToBeExported" interface="com.xyz.MessageService"/> <bean id="beanToBeExported" scope="bundle" class="com.xyz.MessageServiceImpl"/>
The OSGi Service Platform Core Specification defines the term service interface to represent the specification of a service's public methods. Typically this will be a Java interface, but the specification also supports registering service objects under a class name, so the phrase service interface can be interpreted as referring to either an interface or a class.
There are several options for specifying the service
interface(s) under which the exported service is registered. The
simplest mechanism, shown above, is to use the
interface
attribute to specify a fully-qualified
interface name. To register a service under multiple interfaces the
nested interfaces
element can be used in place of
the interface
attribute.
<osgi:service ref="beanToBeExported"> <osgi:interfaces> <value>com.xyz.MessageService</value> <value>com.xyz.MarkerInterface</value> </osgi:interfaces> </osgi:service>
It is illegal to use both interface
attribute and
interfaces
element at the same time - use only one of them.
Using the auto-export
attribute you can avoid
the need to explicitly declare the service interfaces at all by analyzing the
object class hierarchy and its interfaces.
The auto-export
attribute can have one of four
values:
disabled
: the default value; no auto-detected of service
interfaces is undertaken and the interface
attribute or interfaces
element must be used
instead.
interfaces
: the service will be registered using all of the
Java interface types implemented by the bean to be exported
class-hierarchy
: the service will be registered using the
exported bean's implementation type and super-types
all-classes
: the service will be registered using the exported
bean's implementation type and super-types plus all interfaces
implemented by the bean.
auto-export
and interface(s)
option are not exclusive; both
can be used at the same time for fine grained control over the advertised interfaces if there is such
a need. However, the former option should be enough for most cases.
For example, to automatically register a bean under all of the interfaces that it supports you would declare:
<service ref="beanToBeExported" auto-export="interfaces"/>
Given the interface hierarchy:
public interface SuperInterface {} public interface SubInterface extends SuperInterface {}
then a service registered as supporting the
SubInterface
interface is not
considered a match in OSGi when a lookup is done for services
supporting the SuperInterface
interface. For this
reason it is a best practice to export all interfaces supported by the
service being registered explicitly, using either the
interfaces
element or
auto-export="interfaces"
.
As previously described, an exported service is always
registered with the service property
org.springframework.osgi.bean.name
set to the name
of the bean being exported. Additional service properties can be
specified using the nested service-properties
element. The service-properties
element contains
key-value pairs to be included in the advertised properties of the
service. The key must be a string value, and the value must be a type
recognized by OSGi Filters. See section 5.5 of the OSGi Service
Platform Core Specification for details of how property values are
matched against filter expressions.
The service-properties
element must contain
at least one nested entry
element from the Spring
beans namespace. For example:
<service ref="beanToBeExported" interface="com.xyz.MyServiceInterface"> <service-properties> <beans:entry key="myOtherKey" value="aStringValue"/> <beans:entry key="aThirdKey" value-ref="beanToExposeAsProperty"/> </service-properties> </service>
The Spring Dynamic Modules roadmap includes support for exporting properties registered in the OSGi Configuration Administration service as properties of the registered service. See Appendix E, Roadmap for more details.
Spring will manage explicit dependencies of a service element,
ensuring for example that the bean to be exported as a service is
fully constructed and configured before exporting it. If a service has
implicit dependencies on other components (including other service
elements) that must be fully initialized before the service can be
exported, then the optional depends-on
attribute
can be used to express these dependencies.
<service ref="beanToBeExported" interface="com.xyz.MyServiceInterface" depends-on="myOtherComponent"/>
The OSGi Service Platform Core Specification (most current
version is 4.1 at time of writing) does not specify what types and
resources are visible through the context class loader when an
operation is invoked on a service obtained via the service registry.
Since some services may use libraries that make certain assumptions
about the context class loader, Spring Dynamic Modules enables you to
explicitly control the context class loader during service execution.
This is achieved using the option
context-class-loader
attribute of the service
element.
The permissible values for the
context-class-loader
attribute are
unmanaged
(the default) and
service-provider
. When the
service-provider
value is specified, Spring Dynamic
Modules ensures that the context class loader can see all of the
resources on the class path of the bundle exporting the service.
When setting context-class-loader
to service-provider
, the service object will be proxied to
handle the class loader. If the service advertises any concrete class then CGLIB library is required .
When registering a service with the service registry, you may
optionally specify a service ranking (see section 5.2.5 of the OSGi
Service Platform Core Specification). When a bundle looks up a service
in the service registry, given two or more matching services the one
with the highest ranking will be returned. The default ranking value
is zero. To explicitly specify a ranking value for the registered
service, use the optional ranking
attribute.
<service ref="beanToBeExported" interface="com.xyz.MyServiceInterface" ranking="9"/>
As a summary, the following table lists the attributes names, possible values and a short description for each of them.
Table 5.1. OSGi <service> attributes
Name | Values | Description |
---|---|---|
interface | fully qualified class name (such as java.lang.Thread ) | the fully qualified name of the class under which the object will be exported |
ref | any bean name | Reference to the named bean to be exported as a service in the service registry. |
context-class-loader | unmanaged | service-provider | Defines how the context class loader will be managed when an operation is invoked on the
exported service. The default value is unmanaged which means that no management of
the context class loader is attempted. A value of service-provider guarantees that
the context class loader will have visibility of all the resources on the class path of
bundle exporting the service. |
auto-export | disabled | interfaces | class-hierarchy | all-classes | Enables Spring to automatically manage the set of service interfaces advertised for the
service. By default this facility is disabled . A value of interfaces advertises all
of the Java interfaces supported by the exported service. A value of class-hierarchy
advertises all the Java classes in the hierarchy of the exported service. A value of
all-classes advertises all Java interfaces and classes. |
ranking | any integer value | Specify the service ranking to be used when advertising the service. Default value is 0. |
The service defined by a service
element is
registered with the OSGi service registry when the application context
is first created. It will be unregistered automatically when the
bundle is stopped and the application context is disposed.
If you need to take some action when a service is unregistered
because its dependencies are not satisfied (or when it is registered),
then you can define a listener bean using the nested
registration-listener
element.
The declaration of a registration listener must use either the
ref
attribute to refer to a top-level bean
definition, or declare an anonymous listener bean inline. For
example:
<service ref="beanToBeExported" interface="SomeInterface"> <registration-listener ref="myListener" (1) registration-method="serviceRegistered" (2) unregistration-method="serviceUnregistered"/> (2) <registration-listener registration-method="register"> (3) <bean class="SomeListenerClass"/> (4) </registration-listener> </service>
(1) | Listener declaration referring to a top-level bean declaration. |
(2) | Indicate the |
(3) | Declare only a |
(4) | Nested listener bean declaration. |
The optional registration-method
and
unregistration-method
attributes specify the names
of the methods defined on the listener bean that are to be invoked
during registration and unregistration. A registration and unregistration
callback methods must have a signature matching one of the following formats:
public void anyMethodName(ServiceType serviceInstance, Map serviceProperties);
public void anyMethodName(ServiceType serviceInstance, Dictionary serviceProperties);
where ServiceType
can be any type compatible
with the exported service interface of the service.
The register callback is invoked when the service is initially registered at startup, and whenever it is subsequently re-registered. The unregister callback is invoked during the service unregistration process, no matter the cause (such as the owning bundle stopping).
Spring-DM will use the declared ServiceType
argument type
and invoke the registration/unregistration method only when a service of a compatible type
will be registered/unregistered.
serviceProperties
represents a map holding all the properties
of the registered/unregistered service. To preserve compatibility with the OSGi specification
this argument can be cast, if needed, to a java.util.Dictionary
.
While we discourage, it is possible to implement a Spring-DM specific interface, namely
org.springframework.osgi.service.exporter.OsgiServiceRegistrationListener
which avoids the need
to declare the registration-method
and unregistration-method
.
However, by implementing OsgiServiceRegistrationListener
, your code
becomes Spring-DM aware (which goes against the POJO philosophy).
It is possible for a listener to implement OsgiServiceRegistrationListener
interface and
declare custom methods. In this case, the Spring-DM interface methods will be called first, followed by the custom methods.
Spring Dynamic Modules supports the declaration of beans that represent services accessed via the OSGi Service Registry. In this manner references to OSGi services can be injected into application components. The service lookup is made using the service interface type that the service is required to support, plus an optional filter expression that matches against the service properties published in the registry.
For some scenarios, a single matching service that meets the
application requirements is all that is needed. The
reference
element defines a reference to a single
service that meets the required specification. In other scenarios,
especially when using the OSGi whiteboard
pattern, references to all available
matching services are required. Spring Dynamic Modules supports the
management of this set of references as a List
,
Set
collection.
The reference
element is used to define a
reference to a service in the service registry.
Since there can be multiple service matching a given description,
the service returned is the service that would be returned by a call to
BundleContext.getServiceReference
. This means that
the service with the highest ranking will be returned, or if there is
a tie in ranking, the service with the lowest service id (the service
registered first with the framework) is returned (please see Section 5
from the OSGi spec for more information on the service selection algorithm).
The interface
attribute identifies the service
interface that a matching service must implement. For example, the
following declaration creates a bean
messageService
, which is backed by the service
returned from the service registry when querying it for a service
offering the MessageService
interface.
<reference id="messageService" interface="com.xyz.MessageService"/>
Just like the service
declaration, when specifying
multiple interfaces, use the nested interfaces
element instead
of interface
attribute:
<osgi:reference id="importedOsgiService"> <osgi:interfaces> <value>com.xyz.MessageService</value> <value>com.xyz.MarkerInterface</value> </osgi:interfaces> </osgi:reference>
It is illegal to use both interface
attribute and
interfaces
element at the same time - use only one of them.
The bean defined by reference element implements all of the
advertised interfaces of the service that are visible to the bundle (called
greedy proxying).
If the registered service interfaces include Java class types (as
opposed to interface types) then support for these types is subject to
the restrictions of Spring's AOP implementation (see the Spring
Reference Guide). In short, if the specified interfaces are classes
(rather then interfaces), then cglib
library must be
available, and final
methods are not
supported.
The optional filter
attribute can be used
to specify an OSGi filter expression and constrains the service
registry lookup to only those services that match the given
filter.
For example:
<reference id="asyncMessageService" interface="com.xyz.MessageService" filter="(asynchronous-delivery=true)"/>
will match only OSGi services that advertise MessageService
interface and have the property named asynchronous-delivery
set to value true
.
The bean-name
attribute is a convenient
short-cut for specifying a filter expression that matches on the
bean-name
property automatically set when exporting a bean using the
service
element (see Section 5.1, “Exporting a Spring bean as an OSGi service”).
For example:
<reference id="messageService" interface="com.xyz.MessageService" bean-name="defaultMessageService"/>
will match only OSGi services that advertise MessageService
interface and have the property named org.springframework.osgi.bean.name
set
to value defaultMessageService
. In short, this means finding all Spring-DM exported
beans that implement interface MessageService
and are named
defaultMessageService
.
The cardinality
attribute is used to
specify whether or not a matching service is required at all times.
A cardinality value of 1..1
(the default)
indicates that a matching service must always be available. A
cardinality value of 0..1
indicates that a
matching service is not required at all times (see section 4.2.1.6
for more details). A reference
with cardinality
1..1
is also known as a
mandatory service reference and, by default,
application context creation is deferred until the reference is
satisfied.
The depends-on
attribute is used to specify
that the service reference should not be looked up in the service
registry until the named dependent bean has been
instantiated.
The OSGi Service Platform Core Specification (latest
version is 4.1 at time of writing) does not specify what types and
resources are visible through the context class loader when an
operation is invoked on a service obtained via the service registry.
Since some services may use libraries that make certain assumptions
about the context class loader, Spring Dynamic Modules enables you
to explicitly control the context class loader during service
invocation. This is achieved using the option
context-class-loader
attribute of the
reference
element.
The permissible values for the
context-class-loader
attribute are:
client
- during the service invocation,
the context class loader is guaranteed to be
able to see types on the classpath of the invoking bundle.
This is the default option.
service-provider
- during the service invocation,
the context class loader is guaranteed to be
able to see types on the classpath of the bundle exporting
the service.
unmanaged
- no context class loader
management will occur during the service invocation
As a summary, the following table lists the reference
element
attributes names, possible values and a short description for each of them.
Table 5.2. OSGi <reference> attributes
Name | Values | Description |
---|---|---|
interface | fully qualified class name (such as java.lang.Thread ) | The fully qualified name of the class under which the object will be exported. |
filter | OSGi filter expression (such as ((asynchronous-delivery=true) ) | OSGi filter expression that is used to constrain the set of matching services in the service registry. |
bean-name | any string value | Convenient shortcut for specifying a filter expression that matches on the bean-name property that is automatically advertised for beans published using the <service> element. |
context-class-loader | client | service-provider | unmanaged | Defines how the context class loader is managed when invoking operations on a service
backing this service reference. The default value is client which means that the context
class loader has visibility of the resources on this bundle's classpath. Alternate
options are service-provider which means that the context class loader has visibility of
resources on the bundle classpath of the bundle that exported the service, and unmanaged
which does not do any management of the context class loader. |
cardinality | 0..1 | 1..1 | Defines the required cardinality of the relationship to the backing service. If not specified,
the default-cardinality attribute will apply. A value is '1..1' means that a backing service
must exist (this is a mandatory service reference). A value of '0..1' indicates that it is
acceptable to be no backing service (an optional service reference). |
timeout | any positive long | The amount of time (in milliseconds) to wait for a backing service to be
available when an operation is invoked. If not specified, the default-timeout attribute will apply.
|
The bean defined by the reference
element
is unchanged throughout the lifetime of the application context
(the object reference remains constant). However, the OSGi service
that backs the reference may come and go at any time. For a
mandatory service reference (cardinality 1..1
),
creation of the application context will block until a matching
service is available. For an optional service reference
(cardinality 0..1
), the
reference bean will be created immediately, regardless of whether or
not there is currently a matching service.
When the service backing a reference
bean
goes away, Spring Dynamic Modules tries to replace the backing
service with another service matching the reference criteria. An
application may be notified of a change in backing service by
registering a listener
. If no matching service is
available, then the reference
is said to be
unsatisfied. An unsatisfied mandatory service
causes any exported service (service
bean) that
depends on it to be unregistered from the service registry until
such time as the reference is satisfied again. See
Section 5.5, “Relationship between the service exporter and service importer” for more information.
When an operation is invoked on an unsatisfied
reference
bean (either optional or mandatory),
the invocation blocks until the reference becomes satisfied. The
optional timeout
attribute of the
reference
element enables a timeout value (in
milliseconds) to be specified. If a timeout value is specified and
no matching service becomes available within the timeout period, an
unchecked ServiceUnavailableException
is
thrown.
Spring-DM can automatically convert a managed OSGi service to
service reference. That is, if the property into which a reference bean
is to be injected, has type ServiceReference
(instead of the service
interface supported by the reference), then the managed OSGi
ServiceReference
for the service will be injected
in place of the service itself:
public class BeanWithServiceReference { private ServiceReference serviceReference; private SomeService service; // getters/setters ommitted }
<reference id="service" interface="com.xyz.SomeService"/> <bean id="someBean" class="BeanWithServiceReference"> <property name="serviceReference" ref="service"/> (1) <property name="service" ref="service"/> (2) </bean>
(1) | Automatic managed service to |
(2) | Managed service is injected without any conversion |
ServiceReference
is managed by Spring-DM and will change
at the same time as the referenced backing OSGi service instance.
Sometimes an application needs access not simply to any service
meeting some criteria, but to all services
meeting some criteria. Spring-DM allows the matching services may be held in a
List
or Set
(optionally sorted).
The difference between using a List
and a
Set
to manage the collection is one of equality.
Two or more services published in the registry (and with distinct
service ids) may be "equal" to each other, depending on the
implementation of equals used by the service implementations. Only one
such service will be present in a set, whereas all services returned
from the registry will be present in a list. For more details on collections,
see this
tutorial.
The set
and list
schema elements
are used to define collections of services with set or list semantics
respectively.
These elements support the attributes
interface
, filter
,
bean-name
, cardinality
, and
context-class-loader
, with the same semantics as for
the reference
element. The allowable values for the
cardinality
attribute are 0..N
and 1..N
.
A cardinality value of
0..n
indicates that it is permissible for their to
be no matching services. A cardinality value of
1..n
indicates that at least one matching service
is required at all times. Such a reference is considered a
mandatory reference and any exported services
from the same bundle (service
defined beans) that
depend on a mandatory reference will automatically be unregistered
when the reference becomes unsatisfied, and reregistered when the
reference becomes satisfied again.
The bean defined by a list
element is of type
java.util.List
. The bean defined by a
set
element is of type
java.util.Set
.
The following example defines a bean of type List
that
will contain all registered services supporting the
EventListener
interface:
<list id="myEventListeners" interface="com.xyz.EventListener"/>
The members of the collection defined by the bean are managed dynamically by Spring. As matching services are registered and unregistered in the service registry, the collection membership will be kept up to date. Each member of the collection supports the service interfaces that the corresponding service was registered with and that are visible to the bundle.
Spring-DM supports sorted collections as well, both for set and list.
It is possible to specify a sorting order using either the
comparator-ref
attribute, or the nested
comparator
element. The
comparator-ref
attribute is used to refer to a
named bean implementing java.util.Comparator
. The
comparator
element can be used to define an inline
bean. For example:
<set id="myServices" interface="com.xyz.MyService" comparator-ref="someComparator"/> <list id="myOtherServices" interface="com.xyz.OtherService"> <comparator> <beans:bean class="MyOtherServiceComparator"/> </comparator> </list>
To sort using a natural ordering instead of an explicit
comparator, you can use the natural-ordering
element inside of comparator
. You need to specify
the basis for the natural ordering: based on the service references,
following the ServiceReference
natural ordering
defined in the OSGi Core Specification section 6.1.2.3; or based on
the services themselves (in which case the services must be
Comparable
).
<list id="myServices" interface"com.xyz.MyService"> <comparator><natural-ordering basis="services"/></comparator> </list> <set id="myOtherServices"interface="com.xyz.OtherService"> <comparator><natural-ordering basis="service-references"/></comparator> </set>
For a sorted set, a SortedSet
implementation will be created.
However, since JDK API do not provide a dedicated SortedList
interface,
the sorted list will implement only the List
interface.
list
and set
elements support all the attributes available to
reference
element except the timeout
attribute.
See the following table as a summary of the list
and set
element
attribute names, possible values and a short description for each of them.
Table 5.3. <list>/<set> attributes
Name | Values | Description |
---|---|---|
interface | fully qualified class name (such as java.lang.Thread ) | The fully qualified name of the class under which the object will be exported. |
filter | OSGi filter expression (such as ((asynchronous-delivery=true) ) | OSGi filter expression that is used to constrain the set of matching services in the service registry. |
bean-name | any string value | Convenient shortcut for specifying a filter expression that matches on the bean-name property that is automatically advertised for beans published using the <service> element. |
context-class-loader | client | service-provider | unmanaged | Defines how the context class loader is managed when invoking operations on a service
backing this service reference. The default value is client which means that the context
class loader has visibility of the resources on this bundle's classpath. Alternate
options are service-provider which means that the context class loader has visibility of
resources on the bundle classpath of the bundle that exported the service, and unmanaged
which does not do any management of the context class loader. |
cardinality | 0..N | 1..N | Defines the required cardinality of the relationship to the backing service. If not specified,
the default-cardinality attribute will apply. A value is '1..N' means that a backing service
must exist (this is a mandatory service reference). A value of '0..N' indicates that it is
acceptable to be no backing service (an optional service reference). |
comparator-ref | any string value | Named reference to a bean acting as comparator for the declaring collection. Declaring a comparator automatically makes the declaring collection sorted. |
The table below lists the attributes available for the comparator/natural
sub element.
Table 5.4. collection <comparator> attributes
Name | Values | Description |
---|---|---|
basis | service | service-reference | Indicate the element on which natural ordering should apply - service for considering
the service instance and service-reference for considering the service reference instead of the service. |
A collection of OSGi services will change its content during the lifetime of the application context since it needs to reflect the state of the OSGi space. As service are registered and unregistered, they will be added or removed from the collection.
While a reference
declaration will try to
find a replacement if the backing service is unregistered, the collection
will simply remove the service from the collection.
Like reference
, a collection with cardinality 1..N
is said to be mandatory while a collection with cardinality 0..N
is referred to as being optional.
If no matching service is available then only mandatory collections become
unsatisfied.
That is if no service is available invoking an operation on:
ServiceUnavailableException
.Just like reference
, mandatory collections
will trigger the unregistration of any exported service that depends
upon it. See
Section 5.5, “Relationship between the service exporter and service importer” for more information.
The recommend way of traversing a collection is by using an Iterator
.
However, since OSGi services can come and go, the content of the managed service collection will be adjusted
accordingly. Spring-DM will transparently update all Iterator
s held by
the user so it is possible to safely traverse the collection while it is being modified. Moreover, the
Iterator
s will reflect all the changes made to the collection, even if
they occurred after the Iterator
s were created (that is during the iteration).
Consider a case where a collection shrinks significantly (for example a big number of OSGi
services are shutdown) right after an iteration started.
To avoid dealing with the resulting 'dead' service references,
Spring-DM iterators do not take collection snapshots (that can be inaccurate)
but rather are updated on each service event so they reflect the latest collection state,
no matter how fast or slow the iteration is.
It is important to note that a service update will only influence Iterator
operations that are executed after the event occurred. Services already returned by the iterator will not be
updated even if the backing service has been unregistered. As a side note, if an operation is invoked on
such a service that has been unregistered, a ServiceUnavailableException
will be thrown.
To conclude, while a reference
declaration will search for candidates in case the
backing service has been unregistered, a service collections will not replace unregistered services returned
to the user. However, it will remove the unregistered services from the collection so future iterations will not
encounter them.
Please note that the Iterator
contract is guaranteed meaning that
next()
method always obey the result of the previous
hasNext()
invocation.
Table 5.5. Dynamic service collection Iterator
contract
hasNext() returned value | next() behaviour |
---|---|
true | Always return a non-null value, even when the collection has shrunk as services when away. |
false | per Iterator contract, NoSuchElementException is thrown.
This applies even if other services are added to the collection |
The behaviour described above, offers a consistent view over the collection even if its structure changes during iteration.
To simply refresh the iterator, call hasNext()
again. This will force the
Iterator
to check again the collection status for its particular entry in the iteration.
In addition, any elements added to the collection during iteration over a sorted collection will only be visible if the iterator has not already passed their sort point.
Whether you are using reference
or set
or list
, Spring Dynamic
Modules will manage the backing service. However there are cases
where the application needs to be aware when the backing service
is updated.
Such applications, that need to be aware of when the service
backing a reference
bean is bound and unbound, can
register one or more listeners using the nested
listener
element.
This element is available on both reference
and
set
, list
declarations.
In many respects, the service importer listener declaration
is similar to the service exporter listener declaration
(Section 5.1.7, “Service registration and unregistration lifecycle”).
The listener
element refers to a bean (either by name,
or by defining one inline)
that will receive bind and unbind notifications. If this bean
implements Spring-DM's
org.springframework.osgi.service.importer.OsgiServiceLifecycleListener
interface, then the bind
and
unbind
operations in this interface will be
invoked. Instead of implementing this interface (or in addition),
custom bind and unbind callback methods may be named.
An example of declaring a listener that implements
OsgiServiceLifecycleListener
:
<reference id="someService" interface="com.xyz.MessageService"> <listener ref="aListenerBean"/> </reference>
An example of declaring an inline listener bean with custom bind and unbind methods:
<reference id="someService" interface="com.xyz.MessageService"> <listener bind-method="onBind" unbind-method="onUnbind"> <beans:bean class="MyCustomListener"/> </listener> </reference>
If the listener bean implements the
OsgiServiceLifecycleListener
interface
and the listener definition specifies custom
bind and unbind operations then both the
OsgiServiceLifecycleListener
operation and the
custom operation will be invoked, in that order.
The signature of a custom bind or unbind method must be one of:
public void anyMethodName(ServiceType service, Dictionary properties); public void anyMethodName(ServiceType service, Map properties); public void anyMethodName(ServiceReference ref);
where ServiceType
can be any type. Please note that
bind and unbind callbacks are invoked only
if the backing service matches the type declared in the method signature(
ServiceType
). If you want the callbacks to be called
no matter the type, use java.lang.Object
as a
ServiceType
.
The properties
parameter contains the set of properties
that the service was registered with.
If the method signature has a single argument of type
ServiceReference
then the
ServiceReference
of the service will be passed to
the callback in place of the service object itself.
When the listener is used with a reference
declaration:
reference
becomes unsatisfied).When the listener is used with a collection declaration (set
or
list
):
Again note that service collections there is no notion of service rebind: services are added or removed from the collection.
Bind and unbind callbacks are made synchronously as part of
processing an OSGi serviceChanged
event for the
backing OSGi service, and are invoked on the OSGi thread that
delivers the corresponding OSGi
ServiceEvent
.
The table below lists the attributes available for the reference
listener
sub element.
Table 5.6. OSGi <listener> attributes
Name | Values | Description |
---|---|---|
ref | bean name reference | Name based reference to another bean acting as listener. |
bind-method | string representing a valid method name | The name of the method to be invoked when a backing service is bound. |
unbind-method | string representing a valid method name | The name of the method to be invoked when a backing service is bound. |
While the importer listener provides access to the OSGi service bound at a certain point, it is important to note that the given argument is not
the actual service but a proxy. This can have subtle side effects especially with regards to service class name
and identity. The reason behind using a proxy is to prevent the listener from holding strong reference to the service (which can disappear
at any point). Listeners interested in tracking certain services should not rely on instance equality (==
). Object equality
(equals
/hashcode
) can be used but only if the backing service has exposed the aforementioned methods
as part of its contract (normally by declaring them on a certain published interface/class). If these methods are not published, the proxy will invoke its own method, not the targets. This is on purpose since,
while the proxy tries to be as transparent as possible, it is up to the developer to define the desired semantics.
Thus, it is recommended (especially for reference
importers) to do tracking based on just the service interface/contract
(not identity), service properties (see org.osgi.framework.Constants#SERVICE_ID
) or service notification (bind/unbind).
It is sometime useful for an imported service to know which bundle is using it
at a certain time. To help with this scenarion, in Spring-DM imported services publish
the importing bundle BundleContext
through
LocalBundleContext
class. Each time a method on the importer is invoked,
the caller BundleContext
will be made available, using
a ThreadLocal
, through getInvokerBundleContext()
.
Please be careful when using this class since it ties your code to Spring-DM API.
As mentioned above, Spring-DM exporter and importer allow listeners to be used for receiving notifications on when services are bound, unbound, registered or unregistered. Below you can find some guidance advices when working with listeners:
java.util.Map
instead of java.util.Dictionary
class. The first is an interface while the latter is a deprecated, abstract class. To preserve compatibility, Spring-DM
will pass to the listeners a Map
implementation that can be casted, if needed, to a
Dictionary
.There are cases where an exporter/importer listener needs a reference back to the bean it is defined on:
<bean id="listener" class="cycle.Listener"> (1) <property name="target" ref="importer" /> (2) </bean> <osgi:reference id="importer" interface="SomeService"> (3) <osgi:listener bind-method="bind" ref="listener" /> (4) </osgi:reference>
(1) | Listener bean |
(2) | Dependency listener -> importer |
(3) | Importer declaration |
(4) | Dependency importer -> listener |
The declaration above while valid, creates a dependecy between the listener
and the importer it is defined upon.
In order to create the importer, the listener
has to be resolved and created but in order to do that,
the importer called service
needs to be retrieved (instantiated and configured). This cycle needs to be broken
down so that at least one bean can be fully created and configured. This scenario is supported by Spring-DM
for both exporter and importers however, if the listener is defined as a nested bean, the cycle cannot be resolved:
<osgi:reference id="importer" interface="SomeService"> (1) <osgi:listener bind-method="bind"> (2) <bean class="cycle.Listener"> (3) <property name="target" ref="importer" /> (4) </bean> </osgi:listener> </osgi:reference>
(1) | OSGi service importer |
(2) | Dependency between importer -> listener |
(3) | Nested listener declaration |
(4) | Dependency nested listener -> importer |
The example above will fail since service
bean cannot be initialized as it depends on the
listener. The same cycle was seen before but in this case there is subtle yet big different from
the container perspective - the listener is declared as a nested/inner-bean (hence the missing bean id
).
Inner beans have the same life cycle as their declaring parents and do not have any name. By definition, they are not tracked
by the container and are simply created on demand. Since the importer cannot be partially created and the nested listener cannot
be cached, the container cannot break the cycle and create the beans. While the two configurations shown above seem similar, one works
while the other does not. Another reason to not use cycles unless you really, really have to.
To conclude, if you need inside the listener to hold a reference to the exporter/importer on which the listener is declared,
either declare the listener as a top-level bean (as shown before) or consider doing dependency lookup.
However, the latter approach requires extra contextual information such as the BeanFactory
to use and the bean
name and is more fragile then dependency injection.
For those interested in the technical details, neither the exporter and importer cannot be partially initialized since
they require the application context ClassLoader
which is requested through the
BeanClassLoaderAware
which relies on a buit-in BeanPostProcessor
which is applied only after the bean has been configured and is ready for initialization. If the ClassLoader
was not required then the exporter/importer could have been partially initialized and the case above supported.
The osgi
namespace allows offers two
global attributes for specifying default behaviours for all
importers declared in that file.
Thus, when using the osgi
namespace to enclose
set
, list
or
reference
elements, one can use:
default-timeout
-
can be used to specify the default timeout (in milliseconds) for all
importer elements that do not explicitly specify one. For
example:
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:osgi="http://www.springframework.org/schema/osgi" (1) osgi:default-timeout="5000"> (2) <reference id="someService" interface="com.xyz.AService" .../> (3) <reference id="someOtherService" interface="com.xyz.BService" timeout="1000" .../> (4) </beans:beans>
(1) | Declare |
(2) | Declare |
(3) | This |
(4) | This |
default-cardinality
-
can be used to specify the default cardinality for all
importer elements that do not explicitly specify one.
Possible values are 0..X
and 1..X
where X
is substituted at runtime to 1
for reference
elements or N
for collection types such as set
or list
.
Consider the following example:
<beans:beans xmlns="http://www.springframework.org/schema/osgi" (1) xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans" (2) xmlns:osgi="http://www.springframework.org/schema/osgi" (3) osgi:default-cardinality="0..X" (4) default-lazy-init="false"> (5) <reference id="someService" interface="com.xyz.AService"/> (6) <set id="someSetOfService" interface="com.xyz.BService"/> (7) <list id="anotherListOfServices" interface="com.xyz.CService" cardinality="1..N"/> (8) </beans:beans>
(1) | Declare Spring Dynamic Modules schema as the default namespace. |
(2) | Import Spring Framework beans schema and associate a prefix with its namespace
( |
(3) | Import Spring Dynamic Modules schema and associate a prefix with its namespace
( |
(4) | Declare |
(5) |
|
(6) |
The |
(7) |
The |
(8) | The |
The default-*
attributes allow for concise and shorter declarations as well
as easy propagation of changes (such as increasing or decreasing the timeout).
An exported service may depend, either directly or indirectly,
on other services in order to perform its function. If one of these
services is considered a mandatory dependency
(has cardinality 1..x
) and the
dependency can no longer be satisfied
(because the backing service has gone away and there is no suitable
replacement available) then the exported service that depends on it
will be automatically unregistered from the service registry - meaning
that it is no longer available to clients. If the mandatory dependency
becomes satisfied once more (by registration of a suitable service),
then the exported service will be re-registered in the service
registry.
This automatic unregistering and re-registering of exported
services based on the availability of mandatory dependencies only
takes into account declarative dependencies. If exported service
S
depends on bean A
, which in
turn depends on mandatory imported service M
, and
these dependencies are explicit in the Spring configuration file as
per the example below, then when M
becomes
unsatisfied S
will be unregistered. When
M
becomes satisfied again, S
will be re-registered.
<osgi:service id="S" ref="A" interface="SomeInterface"/> <bean id="A" class="SomeImplementation"> <property name="helperService" ref="M"/> </bean> <!-- the reference element is used to refer to a service in the service registry --> <osgi:reference id="M" interface="HelperService" cardinality="1..1"/>
If however the dependency from A
on
M
is not established through configuration as shown
above, but instead at runtime through for example passing a reference
to M
to A
without any
involvement from the Spring container, then Spring Dynamic Modules
will not track this dependency.
Spring-DM offers a dedicated schema element for interacting with existing
bundles or for installing new ones. While it is not intended to be used as a replacement
for proper OSGi services, the bundle
element offers a very
easy way of executing actions on bundles based on the lifecycle of the application
context.
The bundle
element defines a bean of type
org.osgi.framework.Bundle
. It provides a simple way to
work directly with bundles, including driving their lifecycle. In the
simplest case all you need to do is specify the
symbolic-name
of the bundle you are interested
in:
<bundle id="aBundle" symbolic-name="org.xyz.abundle"/>
The bean aBundle
can now be injected into any property of
type Bundle
.
If the needed bundle is not installed, one can use location
attribute
to indicate install or/and the action
/destroy-action
attributes
provide declarative control over the bundle's lifecycle. The location
attribute is
used to specify a URL where the bundle jar file artifact can be found. The
action
attribute specifies the lifecycle operation to
be invoked on the bundle object. The supported action values are
install
, start
,
update
, stop
, and
uninstall
. These actions have the same semantics as the
operations of the corresponding names defined on the
Bundle
interface (see the OSGi Service Platform Core
Specification), with the exception that pre-conditions are weakened to
allow for example a start action to be specified against a bundle that
is not currently installed (it will be installed first).
The following table shows how actions are interpreted for the given Bundle states:
Table 6.1. <bundle> action
values
Action | UNINSTALLED | INSTALLED/RESOLVED | ACTIVE |
---|---|---|---|
START | installs and starts the bundle | starts the bundle | no action taken, bundle already started |
UPDATE | installs the bundle and then updates it (`Bundle.update()`) | updates the bundle | updates the bundle |
STOP | no action taken | no action taken | bundle is stopped |
UNINSTALL | no action taken | bundle is uninstalled | bundle is stopped and then uninstalled |
For example:
<!-- ensure this bundle is installed and started -->; <bundle id="aBundle" symbolic-name="org.xyz.abundle" location="http://www.xyz.com/bundles/org.xyz.abundle.jar" action="start"/>
The following table lists the bundle
element attributes names,
possible values and a short description for each of them.
Table 6.2. <bundle> attributes
Name | Values | Description |
---|---|---|
symbolic-name | any valid symbolic-name String | The bundle symbolic name of the bundle object. Normally used when interacting with an already installed bundle. |
location | String that can be converted into an URL | Location used to install, update or/and identify a bundle. |
action | start | stop | install | uninstall | update | Lifecyle action to drive on the bundle. The action is executed at startup. |
destroy-action | (same as action) | Lifecyle action to drive on the bundle. The action is executed at shutdown. |
The samples that ship with the Spring Dynamic Modules project
include further support for a virtual-bundle
element
that can be used to create and install OSGi bundles on the fly from
existing artifacts.
By following best practices and using the Spring Dynamic Modules
support, your bean classes should be easy to unit test as they will have
no hard dependencies on OSGi, and the few OSGi APIs that you may interact
with (such as BundleContext
) are interface-based
and easy to mock. Whether you want to do unit testing or
integration testing, Spring-DM can ease your task.
Even though most OSGi API are interfaces and creating mocks using a specialized
library like EasyMock is fairly
simple, in practice the amount of code of setting the code (especially on JDK 1.4)
becomes cumbersome. To keep the tests short and concise, Spring-DM provides OSGi
mocks under org.springframework.osgi.mock
package.
It's up to you to decide whether they are useful or not however, we make extensive use of them inside Spring-DM test suite. Below you can find a code snippet that you are likely to encounter in our code base:
private ServiceReference reference; private BundleContext bundleContext; private Object service; protected void setUp() throws Exception { reference = new MockServiceReference(); bundleContext = new MockBundleContext() { public ServiceReference getServiceReference(String clazz) { return reference; } public ServiceReference[] getServiceReferences(String clazz, String filter) throws InvalidSyntaxException { return new ServiceReference[] { reference }; } public Object getService(ServiceReference ref) { if (reference == ref) return service; super.getService(ref); } }; ... } public void testComponent() throws Exception { OsgiComponent comp = new OsgiComponent(bundleContext); assertSame(reference, comp.getReference()); assertSame(object, comp.getTarget()); }
As ending words, experiment with them and choose whatever style or library you feel most confortable with. In our test suite we use the aforementioned mocks, EasyMock library and plenty of integration testing (see below).
In a restricted environment such as OSGi, it's important to test the visibility and versioning of your classes, the manifests or how your bundles interact with each other (just to name a few).
To ease integration testing, the Spring Dynamic Modules project provides a test class hierarchy
(based on org.springframework.osgi.test.AbstractOsgiTests
) that
provides support for writing regular JUnit
test cases that are then
automatically executed in an OSGi environment.
In general, the scenario supported by Spring-DM testing framework is:
start the OSGi framework (Equinox, Knopflerfish, Felix)
install and start any specified bundles required for the test
package the test case itself into a on the fly
bundle,
generate the manifest (if none is provided) and install it in the OSGi
framework
execute the test case inside the OSGi framework
shut down the framework
passes the test results back to the originating test case instance that is running outside of OSGi
By following this sequence it is trivial to write JUnit-based integration tests for OSGi and have them integration into any environment (IDE, build (ant, maven), etc.) that can work with JUnit.
The rest of this chapter details (with examples) the features offered by Spring-DM testing suite.
While the testing framework contains several classes that offer specific
features, it is most likely that your test cases will extend
org.springframework.osgi.test.AbstractConfigurableBundleCreatorTests
(at least
this is what we use in practice).
Let's extend this class and interact with the OSGi platform through
the bundleContext
field:
public class SimpleOsgiTest extends AbstractConfigurableBundleCreatorTests { public void testOsgiPlatformStarts() throws Exception { System.out.println(bundleContext.getProperty(Constants.FRAMEWORK_VENDOR)); System.out.println(bundleContext.getProperty(Constants.FRAMEWORK_VERSION)); System.out.println(bundleContext.getProperty(Constants.FRAMEWORK_EXECUTIONENVIRONMENT)); } }
Simply execute the test as you normally do with any JUnit test. On Equinox 3.2.x, the output is similar to:
Eclipse 1.3.0 OSGi/Minimum-1.0,OSGi/Minimum-1.1,JRE-1.1,J2SE-1.2,J2SE-1.3,J2SE-1.4}
It's likely that you will see other log statements made by the testing framework during your test execution by these can be disabled and have only an informative value as they don't affect your test execution.
Note that you did not have to create any bundle, write any MANIFEST or bother with imports or exports, let alone starting and shutting down the OSGi platform. The testing framework takes care of these automatically when the test is executed.
Let's do some quering and figure out what the environment in which the tests run is.
A simple way to do that is to query the BundleContext
for the installed bundles:
public void testOsgiEnvironment() throws Exception { Bundle[] bundles = bundleContext.getBundles(); for (int i = 0; i < bundles.length; i++) { System.out.print(OsgiStringUtils.nullSafeName(bundles[i])); System.out.print(", "); } System.out.println(); }
The output should be similar to:
OSGi System Bundle, asm.osgi, log4j.osgi, spring-test, spring-osgi-test, spring-osgi-core, spring-aop, spring-osgi-io, slf4j-api, spring-osgi-extender, etc... TestBundle-testOsgiPlatformStarts-com.your.package.SimpleOsgiTest,
As you can see, the testing framework installs the mandatory requirements required for running the test such as the Spring, Spring-DM, slf4j jars among others.
Besides the Spring-DM jars and the test itself is highly likely that you depend on several libraries or your own code for the integration test.
Consider the following test that relies on Apache Commons Lang:
import org.apache.commons.lang.time.DateFormatUtils; ... public void testCommonsLangDateFormat() throws Exception { System.out.println(DateFormatUtils.format(new Date(), "HH:mm:ssZZ")); } }
Running the test however yields an exception:
java.lang.IllegalStateException: Unable to dynamically start generated unit test bundle ... Caused by: org.osgi.framework.BundleException: The bundle could not be resolved. Reason: Missing Constraint: Import-Package: org.apache.commons.lang.time; version="0.0.0" ... ... 15 more
The test requires org.apache.commons.lang.time
package but there is no bundle
that exports it. Let's fix this by installing a commons-lang bundle.
One can specify the bundles that she wants
to be installed using getTestBundlesNames
or getTestBundles
method. The first one returns an array of String that indicate the bundle
name, package and versioning through as a String while the latter returns an array of
Resource
s that can be used directly for installing the bundles.
That is, use getTestBundlesNames
when you rely on somebody else to locate
(the most common case) the bundles and getTestBundles
when you want to
locate the bundles yourself.
By default, the test suite uses the local maven2
repository to locate the artifacts. The locator expects the bundle String to be a comma separated
values containing the artifact group, name, version and (optionally) type.
It's likely that in the future, various other locators will be available. One can plug in their own
locator through the org.springframework.osgi.test.provisioning.ArtifactLocator
interface.
Let's fix our integration test by installing the required bundle (and some extra osgi libraries):
protected String[] getTestBundlesNames() { return new String[] { "org.springframework.osgi, cglib-nodep.osgi, 2.1.3-SNAPSHOT", "org.springframework.osgi, jta.osgi, 1.1-SNAPSHOT", "org.springframework.osgi, commons-lang.osgi, 2.3-SNAPSHOT" }; }; }
Rerunning the test should show that these bundles are now installed in the OSGi platform.
The testing framework allows a lot of customization to be made. This chapter details some of the existing hooks that you might want to know about. However, these are advanced topics as they increase the complexity of your test infrastructure.
There are cases where the auto-generated test manifest does not suite the needs of the test. For example the manifest requires some different headers or a certain package needs to be an optional import.
For simple cases, one can work directly with the generated manifest - in the example below, the bundle class path is being specified:
protected Manifest getManifest() { // let the testing framework create/load the manifest Manifest mf = super.getManifest(); // add Bundle-Classpath: mf.getMainAttributes().putValue(Constants.BUNDLE_CLASSPATH, ".,bundleclasspath/simple.jar"); return mf; }
Another alternative is to provide your own manifest by overriding getManifestLocations()
:
protected String getManifestLocation() { return "classpath:com/xyz/abc/test/MyTestTest.MF"; }
However each manifest needs the following entry:
“Bundle-Activator: org.springframework.osgi.test.JUnitTestActivator”since without it, the testing infrastructure cannot function properly. Also, one needs to import JUnit, Spring and Spring-DM specific packages used by the base test suite:
Import-Package: junit.framework, org.osgi.framework, org.apache.commons.logging, org.springframework.util, org.springframework.osgi.service, org.springframework.osgi.util, org.springframework.osgi.test, org.springframework.context
Failing to import a package used by the test class will cause the test to fail with a
NoDefClassFoundError
error.
By default, for the on-the-fly bundle, the testing infrastructure uses all the classes, xml and properties files
found under ./target/test-classes
folder. This matches the project layout for maven which is used
(at the moment by Spring-DM). These settings can be configured in two ways:
programmatically by overriding AbstractConfigurableBundleCreatorTests
getXXX
methods.
declaratively by creating a properties file having a similar name with the test case. For example, test
com.xyz.MyTest
will have the properties file named com/xyz/MyTest-bundle.properties
.
If found, the following properties will be read from the file:
Table 7.1. Default test jar content settings
Property Name | Default Value | Description |
---|---|---|
root.dir | file:./target/test-classes | the root folder considered as the jar root |
include.patterns | /**/*.class, /**/*.xml, /**/*.properties | Comma-separated string of Ant-style patterns |
manifest | (empty) | manifest location given as a String. By default it's empty meaning the manifest will be created by the test framework rather then being supplied by the user. |
This option is handy when creating specific tests that need to include certain resources (such as localization files or images).
Please consult AbstractConfigurableBundleCreatorTests
and
AbstractOnTheFlyBundleCreatorTests
tests for more customization hooks.
A useful feature of the testing framework represents the automatic creation of the test manifest based on the test bundle content. The manifest creator component uses byte-code analysis to determine the packages imported by the test classes so that it can generate the proper OSGi directives for them. Since the generated bundle is used for running a test, the creator will use the following assumptions:
No packages will be exported.
The on-the-fly bundle is used for running a test which (usually) consumes OSGi packages for its execution. This behaviour can be changed by customizing the manifest.
Split packages (i.e. classes from the same package can come from different bundles) are not supported.
This means that packages present in the test framework are considered complete and no Import-Package
entry will be generated for them.
To avoid this problem, consider using sub-packages or moving the classes inside one bundle. Note that split packages are discouraged due to the
issues associated with them (see the OSGi Core spec, Chapter 3.13 - Required Bundles).
The test bundle contains only test classes.
The byte-code parser will look only at the test classes hierarchy. Any other class included in the bundle, will not be considered so no imports will be generated for it. Consider customizing the manifest yourself or attaching the extra code as inner classes to the test class. A future version of Spring-DM might alleviate this problem by inspecting all classes included in the test bundle.
The reason behind the lack of such features is the byte-code parser is aimed to be simple and fast at creating test manifests - it is not meant as a general-purpose tool for creating OSGi artifacts.
Spring-DM testing suite builds on top of Spring testing classes. To create an application context
(OSGi specific), one should just override getConfigLocations[]
method and indicate
the location of the application context configuration. At runtime, an OSGi application context will be created
and cached for the lifetime of the test case.
protected String[] getConfigLocations() { return new String[] { "/com/xyz/abc/test/MyTestContext.xml" }; }
The testing framework supports out of the box, three OSGi 4.0 implementations namely: Equinox, Knopflerfish and Felix. To be used, these should be in the test classpath. By default, the testing framework will try to use Equinox platform. This can be configured in several ways:
programmatically through getPlatformName()
method
Override the aforementioned method and indicate the fully qualified name of
the Platform
interface implementation. Users can use the Platforms
class to specify one of the supported platforms:
protected String getPlatformName() { return Platforms.FELIX; }
declaratively
through org.springframework.osgi.test.framework
system property.
If this property is set, the testing framework will use its value as a fully qualified name of a Platform implementation. It that fails, it will fall back to Equinox after logging a warning message. This option is useful for building tools (such as ant or maven) since it indicates a certain target environment without changing and test code.
A built-in feature of the testing framework is the ability to wait until all dependencies are deployed before
starting the test execution. Since the OSGi platforms are concurrent by nature, installing a bundle doesn't mean that
all its services are running. By running a test before its dependency services are fully initialized can cause sporadic
errors that pollute the test results. By default, the testing framework inspects all bundles installed by the user and,
if they are Spring-powered bundles, waits until they are fully started (that is their application context is published
as an OSGi service). This behaviour can be disabled by overriding shouldWaitForSpringBundlesContextCreation
method. Consult AbstractSynchronizedOsgiTests
for more details.
Considering all the functionality offered by the testing framework, one might wonder if this doesn't become a performance bottleneck. First, it's worth noting that all the work done automatically by the testing infrastructure has to be done anyway (such as creating the manifest or creating a bundle for the test or installing the bundles). Doing it manually simply simply does not work as it's too error prone and time consuming. In fact, the current infrastructure started as way to do efficient, automatic testing without worrying about deployment problems and redundancy.
As for the numbers, the current infrastructure has been used internally for the last half a year - our integration tests (around 120) run in about 3:30 on a laptop. Most of this time is spent on starting and stopping the OSGi platform: the "testing framework" takes around 10% (as shown in our profiling so far). For example, the manifest generation has proved to take less then 0.5 seconds in general, while the jar creation around 1 second.
However, we are working on making it even faster and smarter so that less configuration options are needed and the contextual information available in your tests is used as much as possible. If you have any ideas or suggestion, feel free to use our issue tracker or/and mailing list.
Hopefully this chapter showed how Spring-DM testing infrastructure can simplify OSGi integration testing and how it can be customized. Consider consulting the javadocs for more information.
Various appendixes outside the reference documentation.
Appendix A, Compendium Services describes the support provided for the OSGi Compendium Services, including the Configuration Admin service. While the support is included in the 1.0 distribution, it is not guaranteed (yet) to be maintained in a backward-compatible form in future point releases.
Appendix B, Extensions describes extensions that are included in the 1.0 distribution, but are not guaranteed to be maintained in a backward-compatible form in future point releases. We anticipate these features moving into the core specification over time.
Appendix C, Eclipse Plug-in Development integration describes how to integrate Spring-DM with Eclipse Plug-in Development Environment.
Appendix D, Spring Dynamic Modules Maven Archetype describes the Spring-DM Maven 2 archetype usage.
Appendix E, Roadmap describes some features that are included in the 1.0 distribution but are still considered early-access. The externals of these features may change in future releases. This appendix also discusses other planned features for which no implementation yet exists.
Appendix F, Spring Dynamic Modules Schema defines the schemas provided by Spring Dynamic Modules.
The OSGi Service Platform Service Compendium specification defines a
number of additional services that may be supported by OSGi
implementations. Spring Dynamic Modules supports an additional
"compendium" namespace that provides support for some of these services.
By convention, the prefix osgix
is used for this
namespace.
<?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns="http://www.springframework.org/schema/osgi" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:osgix="http://www.springframework.org/schema/osgi-compendium" xmlns:beans="http://www.springframework.org/schema/beans" xsi:schemaLocation="http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi.xsd http://www.springframework.org/schema/osgi-compendium http://www.springframework.org/schema/osgi-compendium/spring-osgi-compendium.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- use the OSGi namespace elements directly --> <service id="simpleServiceOsgi" ref="simpleService" interface="org.xyz.MyService" /> <!-- qualify compendium namespace elements --> <osgix:property-placeholder persistent-id="com.xyz.myapp"/> </beans:beans>
At present this namespace provides support for the Configuration Admin service. Support for other compendium services may be added in future releases.
Spring Dynamic Modules provides support for sourcing bean
property values from the OSGi Configuration Administration service.
This support is enabled via the
property-placeholder
element. The property
placeholder element provides for replacement of delimited string
values (placeholders) in bean property expressions with values sourced
from the configuration administration service. The required
persistent-id
attribute specifies the persistent
identifier to be used as the key for the configuration dictionary. The
default delimiter for placeholder strings is "${...}".
Given the declarations:
<osgix:property-placeholder persistent-id="com.xyz.myapp"/> <bean id="someBean" class="AClass"> <property name="timeout" value="${timeout}"/> </bean>
Then the timeout
property of
someBean
will be set using the value of the
timeout
entry in the configuration dictionary
registered under the com.xyz.myapp
persistent
id.
The placeholder strings are evaluated at the time that the bean
is instantiated. Changes to the properties made via Configuration
Admin subsequent to the creation of the bean do
not result in re-injection of property values.
See the managed-service
and
managed-service-reference
elements documented in
appendix B if you require this level of integration. The
placeholder-prefix
and
placeholder-suffix
attributes can be used to change
the delimiter strings used for placeholder values.
It is possible to specify a default set of property values to be
used in the event that the configuration dictionary does not contain
an entry for a given key. The defaults-ref
attribute can be used to refer to a named bean of
Properties
or Map
type. Instead
of referring to an external bean, the
default-properties
nested element may be used to
define an inline set of properties.
<osgix:property-placeholder persistent-id="com.xyz.myapp"> <default-properties> <property name="productCategory" value="E792"/> <property name="businessUnit" value="811"/> </default-properties> </osgix:property-placeholder>
The persistent-id
attribute must refer to the
persistent-id of an OSGi ManagedService
, it is a
configuration error to specify a factory persistent id referring to a
ManagedServiceFactory
.
Support for directly accessing configuration objects and their associated dictionaries, and for instantiating beans directly from configuration objects is on the Spring Dynamic Modules road map. See Appendix E, Roadmap for more information.
This appendix describes extensions to the core functionality that are shipped with the 1.0 distribution, but are not guaranteed to have backwards compatibility across point releases. We anticipate these features migrating into the core specification in future releases.
The
org.springframework.osgi.extensions.annotation
bundle
that ships with Spring Dynamic Modules provides early access to
annotation-based support for injecting references to OSGi services. JDK
1.5 or above is required to use this feature.
Bean class (setter) methods may be annotated with
org.springframework.osgi.extensions.annotation.ServiceReference
.
By default the property type of the annotated property is used to look
up a service with a matching service interface in the OSGi service
registry and inject the result. For example, given the
configuration:
<bean id="annotationDriven" class="MyAnnotationDrivenBeanClass">
and the class declaration:
public class MyAnnotationDrivenBeanClass { @ServiceReference public void setMessageService(MessageService aService) { ... } }
then a service lookup for services implementing the
MessageService
interface will be performed, and the
best match (using the same algorithm as documented for the
reference
element) will be injected.
The ServiceReference
annotation class has a
number of attributes that can be used to control the service lookup (for
example, to specify a filter string) that mirror the options provided by
the reference
element. See the javadoc for more
information.
Eclipse PDE “provides comprehensive OSGi tooling, which makes it an ideal environment for component programming, not just Eclipse plug-in development”. In fact, Eclipse IDE is built on top of OSGi and uses at its core the Equinox OSGi implementation. Moreover, all the Eclipse plug-ins are OSGi bundles. This makes Eclipse with PDE a very attractive tool for creating OSGi bundles. While Spring Dynamic Modules artifacts can be integrated as normal libraries, through Spring IDE, Spring-DM can be installed as a target platform ready to be used with PDE.
The following steps illustrate how to install Spring IDE extension for OSGi and how to use it in your project. Please see Spring IDE installation page for information on its requirement and install process.
Set up nightly update site
At the moment, the OSGi extension is available only on Spring-IDE nightly builds update site. Add it to the Eclipse configuration by opening the software update menu:
and create a new update site pointing to http://www.springide.org/updatesite_nightly
Select Spring IDE OSGi extension
After using the nightly update site and performing the update, Eclipse will show the search results. Unfold the Extension menu and select Spring IDE OSGi Extension
:
and proceed with the instalation.
Select Spring Dynamic Modules Target Platform
Once the plug-in has been installed, Spring Dynamic Modules can be selected as a PDE target platform. Select Window/Preferences/Plug-in Development and then Target Platform.
Select the Spring-DM version that you desire from the Pre-defined Target (1) drop box and press Load Target (2). Eclipse will load the target and all bundles defined by it - this includes Spring-DM bundles and all of its dependencies (SLF4J is used for logging). The configuration can be customised appropriately by removing and adding bundles.
In its current form, the plug-in offers two predefined targets - one for the stable released versions and one for the SNAPSHOT/nightly Spring DM jars. The latter does not contain any jars as it is expected for the user to download them manually. Simply locate the path where the plug-ins should be located (3), enter that folder and do a
mvn install
The latest Spring-DM SNAPSHOT will be downloaded along with all of its dependencies. Simply click on the reload button (4) and Eclipse will pick up the bundles.
Select PDE perspective
Once the installation is completed just select the PDE perspective:
and the Spring-DM and its dependencies should be available in the plug-ins view:
As part of the distribution, Spring-DM provides a Maven archetype which creates the basic structure of a Java project that uses Spring DM, especially useful to new users. To run the archetype (and create the new project), simply run the following command line:
mvn archetype:create \ -DarchetypeGroupId=org.springframework.osgi \ -DarchetypeArtifactId=spring-osgi-bundle-archetype \ -DarchetypeVersion=${version} \ -DgroupId=<your-project-groupId> \ -DartifactId=<your-project-artifactId> \ -Dversion=<your-project-version>
\
is used as a convenience to break the long line into smaller piecesThe result of the command, is a Maven 2 project that defines a simple bean, configures it using
src/main/resources/META-INF/spring/bundle-context.xml
and src/main/resources/META-INF/spring/bundle-context-osgi.xml
and provides unit and (out of the OSGi container) integration tests. The project is packaged as an OSGi bundle.
Notice that by default, the project does not contain a MANIFEST.MF for your project. The Maven infrastructure will generate it, through Apache Felix bundle plug-in. To do that, run the following (from the project root):
mvn package
META-INF
folder
while Spring configuration files under src/main/resources/META-INF
directory.This will compile your project, pack it as a jar and create the OSGi manifest based on your classes under /META-INF
folder (so
that users running Eclipse PDE can use it right away. To generate the manifest, without creating the OSGi bundle, simply run:
mvn org.apache.felix:maven-bundle-plugin:manifest
META-INF/MANIFEST.MF
for OSGi bundle automatically generatedsrc/main/resources/META-INF/spring/bundle-context.xml
is a Spring configuration file that defines the simple bean.src/main/resources/META-INF/spring/bundle-context-osgi.xml
is a spring configuration file ready for you to add bean
definitions from the osgi namespace (services, references etc.)BeanImplTest
case defined to unit test the simple beanBeanIntegrationTest
defined to fire up the non-osgi portions of the application context configuration and test
outside of OSGiBeanOgiIntegrationTest
defined to fire up the osgi portions of the application context configuration and test
inside of OSGi.project
, .classpath
, and build.properties
files created to enable use of this
project directly inside eclipse as a PDE plugin projectThis appendix documents features on the Spring Dynamic Modules roadmap. The design of these features specified here is subject to change. As a most up to date source, please see our issue tracker.
It should be possible to easily instantiate a bean from
the configuration information stored for a
ManagedService
, and a set of beans from the configuration information
stored for a
ManagedServiceFactory
. In addition, updates to the configuration information
should be propagated to beans created in this way.
The
managed-service
element is used to define a bean based on the
configuration information stored under a given
persistent id. It has two mandatory attributes,
class
and
persistent-id
. The
persistent-id
attribute is used to specify the persistent id to be
looked up in the configuration administration service,
class
indicates the Java class of the bean that will be
instantiated.
A simple declaration of a managed service bean would look as follows:
<osgix:managed-service id="myService" class="com.xyz.MessageService" persistent-id="com.xyz.messageservice"/>
The properties of the managed-service
bean
are autowired by name based on the configuration found under the given
persistent id. It is possible to declare regular Spring bean
property
elements within the
managed-service
declaration. If a property value is
defined both in the configuration object stored in the Configuration
Admin service, and in a nested property
element,
then the value from Configuration Admin takes precedence. Property
values specified via property
elements can
therefore be treated as default values to be used if none is available
through Configuration Admin.
It is possible for the configuration data stored in
Configuration Admin to be updated once the bean has been created. By
default, any updates post-creation will be ignored. To receive
configuration updates, the update-strategy
attribute can be used with a value of either
bean-managed
or
container-managed
.
The default value of the optional
update-strategy
attribute is
none
. If an update strategy of
bean-managed
is specified then the
update-method
attribute must also be used to
specify the name of a method defined on the bean class that will be
invoked if the configuration for the bean is updated. The update
method must have one of the following signatures:
public void anyMethodName(Map properties) public void anyMethodName(Map<String,?> properties); // for Java 5 public void anyMethodName(Dictionary properties);
When an update strategy of container-managed
is specified then the container will autowire the bean instance by
name based on the new properties received in the update. For
container-managed
updates, the bean class must
provide setter methods for the bean properties that it wishes to have
updated. Container-managed updates cannot be used in conjunction with
constructor injection. Before proceeding to autowire based on the new
property values, a lock is taken on the bean instance. This lock is
released once autowiring has completed. A class may therefore
synchronize its service methods or otherwise lock on the bean instance
in order to have atomic update semantics.
The managed-service-factory
element is
similar to the managed-service
element, but instead
defines a set of beans, one instance for each configuration stored
under the given factory pid. It has two mandatory attributes,
factory-pid
and class
.
A simple managed-service-factory
declaration
would look as follows:
<osgix:managed-service-factory id="someId" factory-pid="org.xzy.services" class="MyServiceClass"/>
This declaration results in the creation of zero or more beans,
one bean for each configuration registered under the given factory
pid. The beans will have synthetic names generated by appending "-"
followed by the persistent id of the configuration object as returned
by Configuration Admin, to the value of the id
attribute used in the declaration of the
managed-service-factory
. For example,
someId-config.admin.generated.pid
.
Over time new configuration objects may be added under the
factory pid. A new bean instance is automatically instantiated
whenever a new configuration object is created. If a configuration
object stored under the factory pid is deleted, then the corresponding
bean instance will be disposed (this includes driving the
DisposableBean
callback if the bean implements
DisposableBean
). The option
destroy-method
attribute of the
managed-service-factory
element may be used to
specify a destroy callback to be invoked on the bean instance. Such a
method must have a signature:
public void anyMethodName();
It is also possible for the configuration of an existing bean to
be updated. The same update-strategy
and
update-method
attributes are available as for the
managed-service
element and with the same semantics
(though obviously only the bean instance whose configuration has been
updated in Configuration Admin will actually be updated). The same
client-locking semantics also apply when using the
container-managed
update strategy
If you need to work directly with the configuration data stored
under a given persistent id or factory persistent id, the easiest way
to do this is to register a service that implements either the
ManagedService
or
ManagedServiceFactory
interface and specify the pid
that you are interested in as a service property. For example:
<service interface="org.osgi.service.cm.ManagedService" ref="MyManagedService"> <service-properties> <entry key="service.pid" value="my.managed.service.pid"/> </service-properties> </service> <bean id="myManagedService" class="com.xyz.MyManagedService"/>
and where the class MyManagedService
implements
org.osgi.service.cm.ManagedService
.
We intend to provide support for automatic publication of service properties sourced from the Configuration Admin service under a given persistent id. This support has yet to be designed but may look as follows:
<service ref="toBeExported" interface="SomeInterface"> <osgix:config-properties persistent-id="pid"/> </service>
Issues to be considered are scoping of a subset of properties to be published (public/private), and automatic updates to published service properties if the value is updated via config admin.
Note that named properties can easily be published as service
properties already without this support, simply by using the
property-placeholder
support.
The current specification does not provide for access to the
ServiceReference
objects for services in a managed
collection (i.e. obtained via a set
or
list
declaration). A future release of Spring Dynamic
Modules will provide an easy means of gaining access to these
references.
A future release of Spring Dynamic Modules may offer the following additional guarantee with respect to application context creation and start levels:
Application context creation happens asynchronously. However, the
extender bundle does guarantee that the creation of all application
contexts for bundles at start level n
will be
complete before the creation of any application context at start level
m
, where m > n
. Care must
therefore be taken not to introduce any mandatory dependencies on
services exported by bundles with higher start levels or a deadlock will
be introduced.
In a similar vein, when shutting down the extender bundle,
application contexts at start level m
will be shut
down before application contexts at start level n
,
where m > n
.
A key part of the roadmap for the next release of Spring Dynamic
Modules is built-in support for building web applications out of OSGi
bundles. This will be supported using both an HttpService
provided by a bundle installed into the running OSGi framework, and also by embedding
an OSGi container inside an existing servlet container. Pioneering work
has been done by Martin
Lippert, Bernd
Kolb, and Gerd Wutherich amongst others. Please see our mailing list archive
for more information.
Care needs to be taken when using JPA or Hibernate under OSGi as the persistence engines must have visibility of the persistent types and mapping files. The Spring Dynamic Modules project will be investigating an extension model to make managing this easier when persistent configuration is split across several bundles. See Peter Krien's blog entry on the topic for an insight into the issues.
Also, the project aims to simplify deployment of JDBC drivers and
pooling libraries that at the moment require special DynamicImport-Package
.
While OSGi 4.0 is currently required, work is underway to take advantage of the new features available in 4.1. SpringSource is an active participant in the OSGi Enterprise Expert Group and we hope to help many of the ideas found in the Spring Dynamic Modules project to make their way into the OSGi R5 specification. Spring Dynamic Modules would obviously seek to support any such standards at that point in time.
<?xml version="1.0" encoding="UTF-8" standalone="no"?> <xsd:schema xmlns="http://www.springframework.org/schema/osgi" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:beans="http://www.springframework.org/schema/beans" xmlns:tool="http://www.springframework.org/schema/tool" targetNamespace="http://www.springframework.org/schema/osgi" elementFormDefault="qualified" attributeFormDefault="unqualified" version="1.0"> <xsd:import namespace="http://www.springframework.org/schema/beans"/> <xsd:import namespace="http://www.springframework.org/schema/tool"/> <xsd:annotation> <xsd:documentation><![CDATA[ Namespace support for the core services provided by Spring Dynamic Modules. ]]></xsd:documentation> </xsd:annotation> <xsd:attributeGroup name="defaults"> <xsd:annotation> <xsd:documentation><![CDATA[Defaults for Spring-DM OSGi declarations.]]> </xsd:documentation> </xsd:annotation> <!-- attributes --> <xsd:attribute name="default-timeout" type="xsd:long" default="30000"> <xsd:annotation> <xsd:documentation><![CDATA[ Default timeout (in milliseconds) for all reference (service importers) elements that do not explicitly specify one. Default value is 300000 ms (5 minutes). ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="default-cardinality" type="TdefaultCardinalityOptions" default="1..X"> <xsd:annotation> <xsd:documentation><![CDATA[ Default cardinality (of the relationship to the backing service(s)) for all OSGi references (singular or collections) elements that do not explicitly specify one. Default value is '1..X' (resolved to '1..1' for osgi:reference and '1..N' for osgi:list/set) which means that a backing service must exist (this is a mandatory service reference). A value of '0..X' (resolved to '0..1' for osgi:reference and '0..N' for osgi:list/set) indicates that it is acceptable to be no backing service (an optional service reference). ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:attributeGroup> <xsd:simpleType name="TdefaultCardinalityOptions"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="1..X"> <xsd:annotation> <xsd:documentation><![CDATA[ A backing service must exist (this is a mandatory service reference). ]]></xsd:documentation> </xsd:annotation> </xsd:enumeration> <xsd:enumeration value="0..X"> <xsd:annotation> <xsd:documentation><![CDATA[ A backing service can be missing (this is an optional service reference). ]]></xsd:documentation> </xsd:annotation> </xsd:enumeration> </xsd:restriction> </xsd:simpleType> <!-- reference --> <xsd:element name="reference" type="TsingleReference"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines a reference to a service obtained via the OSGi service registry. ]]></xsd:documentation> </xsd:annotation> </xsd:element> <xsd:complexType name="Treference"> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <xsd:sequence minOccurs="0" maxOccurs="unbounded"> <xsd:element name="interfaces" type="beans:listOrSetType" minOccurs="0" maxOccurs="1"> <xsd:annotation> <xsd:documentation><![CDATA[ The set of service interfaces to advertise in the service registry. ]]></xsd:documentation> </xsd:annotation> </xsd:element> <xsd:element name="listener" type="Tlistener" minOccurs="0" maxOccurs="unbounded"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines a listener that will receive notification when a service backing this reference is bound or unbound. ]]></xsd:documentation> </xsd:annotation> </xsd:element> </xsd:sequence> <xsd:attribute name="interface" use="optional" type="xsd:token"> <xsd:annotation> <xsd:documentation><![CDATA[ The service interface that the services obtained via the registry are required to support. By convention this is a Java interface type, but may also be a (non-final) class type. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:expected-type type="java.lang.Class" /> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:attribute> <xsd:attribute name="filter" use="optional" type="xsd:string"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines an OSGi filter expression that is used to constrain the set of matching services in the service registry. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="depends-on" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Used to refer to the name of another bean that this bean depends on. Ensures that the service registry look-up does not happen until after the dependent bean has been created (most commonly used to refer to a bundle bean). ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="bean-name" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Convenient shortcut for specifying a filter expression that matches on the bean-name property that is automatically advertised for beans published using the service element. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="context-class-loader" type="TreferenceClassLoaderOptions" default="client"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines how the context class loader is managed when invoking operations on a service backing this service reference. The default value is 'client' which means that the context class loader has visibility of the resources on this bundle's classpath. Alternate options are 'service-provider' which means that the context class loader has visibility of resources on the bundle classpath of the bundle that exported the service, and 'unmanaged' which does not do any management of the context class loader. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:extension> </xsd:complexContent> </xsd:complexType> <xsd:simpleType name="TreferenceClassLoaderOptions"> <xsd:restriction base="xsd:NMTOKEN"> <xsd:enumeration value="client"/> <xsd:enumeration value="service-provider"/> <xsd:enumeration value="unmanaged"/> </xsd:restriction> </xsd:simpleType> <xsd:complexType name="Tlistener"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines a listener that will be notified when the service backing the enclosing service reference element is bound or unbound. Use either the 'ref' attribute or a nested bean declaration for the listener bean. ]]></xsd:documentation> </xsd:annotation> <xsd:sequence minOccurs="0" maxOccurs="1"> <!-- nested bean declaration --> <xsd:any namespace="##other" minOccurs="1" maxOccurs="1" processContents="skip"/> </xsd:sequence> <!-- shortcut for bean references --> <xsd:attribute name="ref" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Refers by name to the bean that will receive bind and unbind events ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="bind-method" type="xsd:token" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ The name of the method to be invoked when a backing service is bound. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="unbind-method" type="xsd:token" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ The name of the method to be invoked when a backing service is unbound. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:complexType> <!-- single reference --> <xsd:complexType name="TsingleReference"> <xsd:complexContent> <xsd:extension base="Treference"> <xsd:attribute name="cardinality" use="optional" type="TsingleReferenceCardinality"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines the required cardinality of the relationship to the backing service. If not specified, the default-cardinality attribute will apply. A value is '1..1' means that a backing service must exist (this is a mandatory service reference). A value of '0..1' indicates that it is acceptable to be no backing service (an optional service reference). ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="timeout" use="optional" type="xsd:long"> <xsd:annotation> <xsd:documentation><![CDATA[ For a 'reference' element, the amount of time (in milliseconds) to wait for a backing service to be available when an operation is invoked. If not specified, the default-timeout attribute will apply. See also the default-timeout attribute of the osgi element. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:extension> </xsd:complexContent> </xsd:complexType> <xsd:simpleType name="TsingleReferenceCardinality"> <xsd:restriction base="xsd:token"> <xsd:enumeration value="1..1"/> <xsd:enumeration value="0..1"/> </xsd:restriction> </xsd:simpleType> <!-- reference collections (set, list) --> <xsd:element name="list" type="TreferenceCollection"> <xsd:annotation> <xsd:documentation source="java:org.springframework.osgi.service.importer.support.OsgiServiceCollectionProxyFactoryBean"><![CDATA[ Defines a bean of type 'List' that contains all of the services matching the given criteria. The list members are managed dynamically as matching backing services come and go. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:exports type="java.util.List"/> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:element> <xsd:element name="set" type="TreferenceCollection"> <xsd:annotation> <xsd:documentation source="java:org.springframework.osgi.service.importer.support.OsgiServiceCollectionProxyFactoryBean"><![CDATA[ Defines a bean of type 'Set' that contains all of the services matching the given criteria. The set members are managed dynamically as matching backing services come and go. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:exports type="java.util.Set"/> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:element> <xsd:complexType name="TreferenceCollection"> <xsd:complexContent> <xsd:extension base="Treference"> <xsd:sequence minOccurs="0" maxOccurs="1"> <xsd:element name="comparator" type="Tcomparator"> <xsd:annotation> <xsd:documentation source="java:java.util.Comparator"><![CDATA[ Used to define an inline bean of type Comparator that will be used to sort the matching services. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:expected-type type="java.util.Comparator" /> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:element> </xsd:sequence> <xsd:attribute name="comparator-ref" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Used to refer to a named bean implementing the Comparator interface that will be used to sort the matching services. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="cardinality" use="optional" type="TcollectionCardinality"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines the required cardinality of the relationship to the backing services. If not specified, the default-cardinality attribute will apply. A value of '1..N' means that at least one backing service must exist (this is a mandatory service reference. A value of '0..N' indicates that it is acceptable for there to be no backing service (an optional service reference). ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:extension> </xsd:complexContent> </xsd:complexType> <xsd:complexType name="Tcomparator"> <xsd:annotation> <xsd:documentation source="java:java.util.Comparator"><![CDATA[ Used to define an inline bean of type Comparator that will be used to sort the matching services. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:exports type="java.util.Comparator" /> </tool:annotation> </xsd:appinfo> </xsd:annotation> <xsd:choice> <xsd:element name="natural" type="TnaturalOrdering"/> <xsd:sequence minOccurs="1" maxOccurs="1"> <!-- nested bean declaration --> <xsd:any namespace="##other" minOccurs="1" maxOccurs="1" processContents="skip"/> </xsd:sequence> </xsd:choice> </xsd:complexType> <xsd:complexType name="TnaturalOrdering"> <xsd:attribute name="basis" type="TorderingBasis" use="required"/> </xsd:complexType> <xsd:simpleType name="TorderingBasis"> <xsd:restriction base="xsd:token"> <xsd:enumeration value="service"/> <xsd:enumeration value="service-reference"/> </xsd:restriction> </xsd:simpleType> <xsd:simpleType name="TcollectionCardinality"> <xsd:restriction base="xsd:token"> <xsd:enumeration value="1..N"/> <xsd:enumeration value="0..N"/> </xsd:restriction> </xsd:simpleType> <!-- service --> <xsd:element name="service" type="Tservice"/> <xsd:complexType name="Tservice"> <xsd:annotation> <xsd:documentation source="java:org.springframework.osgi.service.exporter.support.OsgiServiceFactoryBean"><![CDATA[ Exports the reference bean as a service in the OSGi service registry. The bean defined by this element is of type org.osgi.framework.ServiceRegistration. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:exports type="org.osgi.framework.ServiceRegistration"/> </tool:annotation> </xsd:appinfo> </xsd:annotation> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <xsd:sequence minOccurs="0" maxOccurs="1"> <xsd:element name="interfaces" type="beans:listOrSetType" minOccurs="0"> <xsd:annotation> <xsd:documentation><![CDATA[ The set of service interfaces to advertise in the service registry. ]]></xsd:documentation> </xsd:annotation> </xsd:element> <xsd:element name="service-properties" minOccurs="0" type="beans:mapType"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines the service properties. ]]></xsd:documentation> </xsd:annotation> </xsd:element> <xsd:element name="registration-listener" type="TserviceRegistrationListener" minOccurs="0" maxOccurs="unbounded"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines a listener that will be notified when this service is registered or unregistered in the OSGi service registry. ]]></xsd:documentation> </xsd:annotation> </xsd:element> <!-- nested bean declaration --> <xsd:any namespace="##other" minOccurs="0" maxOccurs="1" processContents="skip"/> </xsd:sequence> <xsd:attribute name="interface" type="xsd:token" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines the interface to advertise for this service in the service registry. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:expected-type type="java.lang.Class" /> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:attribute> <xsd:attribute name="ref" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Refers to the named bean to be exported as a service in the service registry. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="depends-on" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Used to ensure that the service is not exported to the registry before the named bean has been created. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="context-class-loader" type="TserviceClassLoaderOptions" default="unmanaged"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines how the context class loader will be managed when an operation is invoked on the exported service. The default value is 'unmanaged' which means that no management of the context class loader is attempted. A value of 'service-provider' guarantees that the context class loader will have visibility of all the resources on the class path of bundle exporting the service. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="auto-export" type="TautoExportModes" default="disabled"> <xsd:annotation> <xsd:documentation><![CDATA[ Enables Spring to automatically manage the set of service interfaces advertised for the service. By default this facility is disabled. A value of 'interfaces' advertises all of the Java interfaces supported by the exported service. A value of 'class-hierarchy' advertises all the Java classes in the hierarchy of the exported service. A value of 'all-classes' advertises all Java interfaces and classes. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="ranking" type="xsd:int" default="0"> <xsd:annotation> <xsd:documentation><![CDATA[ Specify the service ranking to be used when advertising the service. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:extension> </xsd:complexContent> </xsd:complexType> <xsd:complexType name="TserviceRegistrationListener"> <xsd:annotation> <xsd:documentation><![CDATA[ Defines a listener that will be notified when the bean is registered or unregistered in the OSGi Service Registry. Use either the 'ref' attribute or a nested bean declaration for the listener bean. ]]></xsd:documentation> </xsd:annotation> <xsd:sequence minOccurs="0" maxOccurs="1"> <!-- nested bean declaration --> <xsd:any namespace="##other" minOccurs="1" maxOccurs="1" processContents="skip"/> </xsd:sequence> <!-- shortcut for bean references --> <xsd:attribute name="ref" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Refers by name to the bean that will receive register and unregister events. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="registration-method" type="xsd:token" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ The name of the method to be invoked when the service is registered. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="unregistration-method" type="xsd:token" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ The name of the method to be invoked when the service is unregistered. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:complexType> <xsd:simpleType name="TserviceClassLoaderOptions"> <xsd:restriction base="xsd:token"> <xsd:enumeration value="service-provider"/> <xsd:enumeration value="unmanaged"/> </xsd:restriction> </xsd:simpleType> <xsd:simpleType name="TautoExportModes"> <xsd:restriction base="xsd:token"> <xsd:enumeration value="disabled"/> <xsd:enumeration value="interfaces"/> <xsd:enumeration value="class-hierarchy"/> <xsd:enumeration value="all-classes"/> </xsd:restriction> </xsd:simpleType> <!-- bundle --> <xsd:element name="bundle" type="Tbundle"> <xsd:annotation> <xsd:documentation source="java:org.springframework.osgi.bundle.BundleFactoryBean"><![CDATA[ Defines a bean representing a Bundle object. May be used to drive bean lifecycle transitions. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:exports type="org.osgi.framework.Bundle"/> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:element> <xsd:complexType name="Tbundle"> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <!-- optional nested bean declaration --> <xsd:sequence minOccurs="0" maxOccurs="1"> <xsd:any namespace="##other" minOccurs="1" maxOccurs="1" processContents="lax"> <xsd:annotation> <xsd:documentation><![CDATA[ OSGi bundle to work with. ]]></xsd:documentation> <xsd:appinfo> <tool:annotation> <tool:expected-type type="org.osgi.framework.Bundle" /> </tool:annotation> </xsd:appinfo> </xsd:annotation> </xsd:any> </xsd:sequence> <xsd:attribute name="symbolic-name" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ The bundle symbolic name of the bundle object. Normally used when interacting with an already installed bundle. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="depends-on" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Indicates that this bundle object should not be created until the named bean has been created. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="location" type="xsd:string" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Location used to install, update or/and identify a bundle. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="action" type="TbundleAction" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Lifecyle action to drive on the bundle. 'start' starts the bundle, installing if necessary. 'stop' stops the bundle if it is currently ACTIVE. 'install' installs the bundle if it is currently uninstalled. 'uninstall' stops the bundle if needed, and then uninstalls it. 'update' installs the bundle if needed, and then invokes the Bundle.update() operation. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="destroy-action" type="TbundleAction" use="optional"> <xsd:annotation> <xsd:documentation><![CDATA[ Lifecyle action to drive on the bundle. 'start' starts the bundle, installing if necessary. 'stop' stops the bundle if it is currently ACTIVE. 'install' installs the bundle if it is currently uninstalled. 'uninstall' stops the bundle if needed, and then uninstalls it. 'update' installs the bundle if needed, and then invokes the Bundle.update() operation. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> <xsd:attribute name="start-level" type="xsd:int" use="optional" default="0"> <xsd:annotation> <xsd:documentation><![CDATA[ Start level to set for the bundle. ]]></xsd:documentation> </xsd:annotation> </xsd:attribute> </xsd:extension> </xsd:complexContent> </xsd:complexType> <xsd:simpleType name="TbundleAction"> <xsd:restriction base="xsd:token"> <xsd:enumeration value="start"/> <xsd:enumeration value="stop"/> <xsd:enumeration value="install"/> <xsd:enumeration value="uninstall"/> <xsd:enumeration value="update"/> </xsd:restriction> </xsd:simpleType> </xsd:schema>
Spring Dynamic Modules would like to thank (in alphabetical order) to : Bill Gallagher, Olivier Gruber, Richard S. Hall, BJ Hargrave, Peter Kriens, Martin Lippert, Jeff McAffer, Glyn Normington, Gerd Wuetherich for their contributions in the development of this specification.
In addition to this reference documentation, there exist a number of other resources that may help you learn how to use OSGi and Spring Dynamic Modules. These additional, third-party resources are enumerated in this section.