The OSGi term is a trademark belonging to The OSGi Alliance. In order to comply with their guidelines, it was decided that the project name be changed to "Spring Dynamic Modules for OSGi Service Platforms" (aka Spring-DM). The new name is still pending final approval by the OSGi Alliance. The name change was the result of an amicable discussion between the OSGi Alliance and Interface21. Interface21 is a member of the OSGi Alliance, and the OSGi Alliance remain very supportive of the project.
org.springframework.osgi.*.internal packages are
meant (as the name implies) to be private and non-public package. Thus,
there is no documentation, support or compatibility guarantee for
them. In fact, the Spring Dynamic Modules bundle does not even export
them to prevent accidental usage.
If you find classes under this package, which you really, really depend on, then consider raising an issue on JIRA to have access opened up.
Spring Dynamic Modules requires at least Java 1.4, OSGi 4.0 and Spring 2.5. It might be possible to use Spring Dynamic Modules on a lower execution environment (such CDC) but it is not guaranteed to work. Both Spring and Spring Dynamic Modules rely on JavaBeans (java.beans package) which, unfortunately, is missing in most restricted environments. See this PDF for information on CDC profiles. Note that, Spring 2.5 also requires Java 1.4.
Nevertheless, experiences and feedback on running Spring-DM in restricted environments is welcomed - please use our mailing list.
There are no current plans to support other dynamic module frameworks.
See the requirements entry. The OSGi Service Platform is designed to run in very constrained environments however, Spring Dynamic Modules depends on the Spring Framework v2.5 which in turn depends on JDK 1.4. Thus Spring Dynamic Modules cannot run on more constrained environments (such as the OSGi Minimum Execution Environment) unless Spring itself also runs in those environments. There are no current plans to make such a version of Spring. However as existing OSGi developers adopt Spring Dynamic Modules to simplify creation of OSGi applications and the user base expands, the target audience can cover domains much broader than <em>enterprise Java applications</em>. In time this could create a large enough demand to justify the investment needed to allow Spring and Spring-DM to run in restricted environments.
Spring-DM requires an OSGi 4.0 platform. The framework has been tested on Equinox, Felix and Knopflerfish - in fact, the test suite is ran against all of them as part of our continuous integration process.
The best place to start is The Osgi Alliance home and developer pages which provide the OSGi specifications, introductions and many links and blogs on the topic. Please see the reference documentation appendix for more information.
In addition, all OSGi implementation websites host detailed, step-by-step tutorials and introduction.
If you discover any additional materials useful for OSGi newbies, please let us know to update the list. Thank you.
Please see the file called
readme-building.txt found in the source tree.
This exception is thrown only when running on Java 1.4 without backport-util-concurrent bundle installed.
OSGi platform is a concurrent environment. Beans from different application contexts can interact with each other creating cycles between their owning contexts. This means that the backing contexts have to be able to lookup and create/retrieve bean instances, all at the same time, on multiple threads. A traditional synchronised collection allows proper locking and thread coordination and prevents race conditions, but can cause very easily deadlocks.
Consider two contexts each containing two beans:
If both bean A and C are requested by two separate threads at
the same time, this scenario will deadlock since each thread waits for
the other one to release the "bean registry" lock even just for
reading. However, when using a concurrent collection, reading doesn't
require a lock so each thread can interact with the other context
without waiting for a lock. Java 1.5 and upwards provide concurrent
However, since Java 1.4 does not, backport-util-concurrent
library is required.
OSGi platforms do not change the way libraries work, it just enforces tighter classloading. Thus, you can, in most of the cases, use the same logging strategy used in non-OSGi environments.
Spring (and Spring-DM) use internally the commons-logging API which acts as an "ultra-thin bridge between different logging implementations". In OSGi, just like in a non-OSGi environment, Spring and Spring-DM delegate all logging (including initialisation) to the actual commons-logging API implementation.
Out of the box, SLF4J library is provided, which shares the same purpose as commons-logging but without the classloading discovery mechanism that causes loading issues, using static wiring (see the SLF4J site for more info). Please see this question for more details on why commons-logging jar is not used.
Spring-DM uses SLF4J on top of Log4J but this can be
easily changed. As part of log4j initialisation, a
configuration fille needs to be present in the bundle classpath. This
means that the configuration file has to be part of your bundle or one
of its attached fragments. Besides SLF4J, for another OSGi-aware
solution, one can try Pax
To learn more about log4j setup process, follow this link.
The commons-logging project provides the commons-logging API
commons-logging-api-nn.jar) along with an
that provides a wrapper between the API and the actual logging libraries
used underneath (such as log4j, java.util.logging, etc). However, in
order to determine what implementation should be used, commons-logging
library tries to do some classloading-based discovery that is fragile
and can fail unexpectedly. In an strict classloading environment such
as OSGi, this mechanism adds unnecessary complexity - that's why we
decided to use SFL4J which is not just simpler and actively maintained
but is also OSGi-friendly out of the box.
If you have to use commons-logging (for example the jar is required by certain bundles) then try using the most recent version commons-logging version (1.1+) as it provides more options on the discovery process. Below are some settings that can be used to make commons-logging work inside an OSGi environment:
Unfortunately, commons-logging 1.0.x uses the thread context class loader (TCCL) always for loading
loggers implementations. Inside an OSGi environment, the TCCL is undefined and cannot be relied upon.
Since managing the TCCL is almost impossible as most loggers are defined as static fields that need to
resolved on class loading, using a different
LogFactory is advised. One can use
the org.apache.commons.logging.LogFactory system property to specify a different
log factory however, the commons-logging bundle should be able to load this class.
If using commons logging 1.1.x, one can turn off the tccl usage through use_tccl property, part of the commons-logging.properties file. http://commons.apache.org/logging/commons-logging-1.1/troubleshooting.html. Additionally, 1.1.x provides several system properties (such as org.apache.commons.logging.Log.allowFlawedContext, org.apache.commons.logging.Log.allowFlawedDiscovery and org.apache.commons.logging.Log.allowFlawedHierarchy) that can change the behavious of the discovery process. See the LogFactoryImpl javadoc for more details.
In our tests, commons logging 1.1.x can be used with reasonable success inside OSGi. We haven't been able to find a generic configuration for commons logging 1.0.x that works and that does not rely on fragile hacks dependent on the running environment.
It is completely up to you what logging implementation you want Spring-DM to use. To route log messages to the OSGi logging service, just use a commons-logging API implementation that delegates to the OSGi logging service, such as Pax Logging.
OSGi requires JARs to contain certain
MANIFEST.MF entries which indicate what classes are
required and shared by each archive. This means that tradition jars cannot be used inside an OSGi environment.
To solve the problem one can:
Wrap the necessary jars with proper OSGi manifest. While this can be done by hand, we strongly recommend Peter Kriens excellent bnd tool which can do this for you automatically. For Maven, see Felix maven-bundle-plugin.
Include the jar inside your OSGi bundle and include it in the bundle classpath through Bundle-ClassPath directive. See the OSGi specification for more information.
This problem is likely to be caused by bad class wiring. All 1.3+ JDKs include incomplete javax.transaction and javax.transaction.xa packages for usage inside ORB environments. To address the problem, use a proper JTA library which contains all the classes from the forementioned packages and exports them with a specific version to prevent confusion.
Spring-DM wraps JTA 1.1 library for OSGI environments which can be found at Spring snapshot repository. One can deploy this library and specify version 1.1 for javax.transaction* packages inside Import-Package header. By specifying the version, one can be sure that the proper package is used.
Note that JTA 1.1 is compatible with version 1.0.1.
autoExport flag, part of the service exporter, will discover and
include for exporting only the visible interfaces/classes implemented
by the service object. Consider class
GenericApplicationContext which implements among
org.springframework.beans.factory package) and
Depending on your OSGi imports, the exporting bundle can see
only one of the packages, none or both. Based on these visibility
settings, the exporter will only export the classes that are 'known'
to the exporting bundle. For example, if the exporting bundle sees
org.springframework.core.io but not
org.springframework.beans.factory, the service will
be exported as a
ResourceLoader but not as a
BeanFactory. In fact, exporting the object as a
BeanFactory will fail since the bundle doesn't see
this interface and thus doesn't know how to handle its contract.
This problem occurs on Spring DM versions up to 1.0 - consider upgrading to 1.0.1 or better. If you are stuck with 1.0 see below. When running an integration test, Spring-DM will duplicate the test instance and execute it inside OSGi. To avoid problems like this one, make sure you are using the same libraries (with the same version) as Spring-DM when running your test. This particular problem for example is caused by a JUnit 3.8.2 vs 3.8.x serialization compatibility. Make sure that you are using at least JUnit 3.8.2 for the execution of your tests.
The above error indicates that some classes, dependend on by others, have a different, incompatible version then the one required. Normally this occur with workspaces (such as Eclipse) that are corrupt or stale. Consider doing a complete clean build or, in case of Eclipse, creating a new workspace.