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/dispose-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.