THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Providing OSGi services
This pages explains how to publish OSGi services with iPOJO. It presents:
- service publication
- service properties publication and management
- service object creation and creation strategies
- service un-registration
- configuration property propagation
- the management of the exposition from the implementation class
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A simple example
The following code snippet shows a simple class implementing the FooService interface:
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{html} h1. Providing OSGi services _This pages explains how to publish OSGi services with iPOJO. It presents:_ * _service publication_ * _service properties publication and management_ * _service object creation and creation strategies_ * _service un-registration_ * _configuration property propagation_ * _the management of the exposition from the implementation class_ {div:class=toc} {toc:maxLevel=4|minLevel=2} {div} h2. A simple example The following code snippet shows a simple class implementing the {{FooService}} interface: {code} @Component @Provides public class FooProviderType1 implements FooService { private String m_foo = "foo"; public void foo() { System.out.println("foo " + m_foo); } } {code} |
To
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provide
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a
...
service,
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the
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implementation
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class
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MUST
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implement
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the
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service
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interface.
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In
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XML,
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to
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provide
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the
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service,
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the
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component
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type
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needs
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to
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contain
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the
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<provides/>
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element:
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{code:xml} <component className="...FooProviderType1"> <provides/> </component> {code} !ps-foo.png! The |
The <provides/>
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or
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@Provides
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suffice
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to
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declare
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that
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each
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instance
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of
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this
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type
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will
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provide
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the FooService (for more info about instances see How-to use iPOJO factories). The provided specifications can be discovered by analyzing the implementation class. By default, all implemented interface are published in the same service registration. iPOJO looks down the entire inheritance tree.
Service Publication
The provided service handler manages service publication. For each declared <provides/>, the handler registers a service. Since the @Provides annotation can be used only once, only one service is registered that provides all interfaces. The service is published as long as the instance is valid. If the instance becomes invalid, the service is removed from the service registry.
By default, it publishes all interfaces implemented by the implementation class of the component class. It collects all super-interfaces (interfaces implemented by implemented interfaces and by the super class). However, it is possible to explicitly declare which service specifications are published with the specifications attribute, such as:
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FooService. The provided specifications can be discovered by analyzing the implementation class. By default, all implemented interface are published in the same service registration. iPOJO looks down the entire inheritance tree. h2. Service Publication The provided service handler manages service publication. For each declared {{<provides/>}}, the handler registers a service. Since the @Provides annotation can be used only once, only one service is registered that provides all interfaces. The service is published as long as the instance is valid. If the instance becomes invalid, the service is removed from the service registry. By default, it publishes all interfaces implemented by the implementation class of the component class. It collects all super-interfaces (interfaces implemented by implemented interfaces and by the super class). However, it is possible to explicitly declare which service specifications are published with the {{specifications}} attribute, such as: {code} @Component @Provides(specifications={FooService.class}) public class FooProviderType1 implements FooService, Runnable { // ... } {code} {info:title=Change in the |
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In the 1.0.0 version and before, the {{
attribute was named {{
. |
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If you use the |
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If the implementation class does not implement any interface, you cannot provide a service. In this case, the handler throws an error. |
Service Properties
You can also attach properties to a service registration. Service properties are attached to published service and allow consumer filtering/selecting providers. A property can be attached to a field (contained in the component implementation class), and so can be handle dynamically.
Let's take a new example very closed of the last one:
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{info} {info:title=Specification checking} If you use the {{specifications}} attribute, the handler checks that all declared interfaces are really implemented by the implementation class. If an interface is not implemented, the handler logs a warning. {info} {info:title=No service} If the implementation class does not implement any interface, you cannot provide a service. In this case, the handler throws an error. {info} h2. Service Properties You can also attach properties to a service registration. Service properties are attached to published service and allow consumer filtering/selecting providers. A property can be attached to a field (contained in the component implementation class), and so can be handle dynamically. Let's take a new example very closed of the last one: {code} @Component @Provides public class FooProviderType1 implements FooService { @ServiceProperty(name="foo", value="Foo") private String m_foo; public void foo() { System.out.println("foo " + m_foo); m_foo = "bar"; } } {code} |
Using
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XML,
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it
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gives:
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} <component classname="...FooProviderType1"> <provides> <property name="foo" field="m_foo" value="Foo"/> </provides> </component> {code} |
The
...
declared
...
property
...
is
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attached
...
to
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the
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m_foo
...
field.
...
This
...
property
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is
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published
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with
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the
...
name
...
foo
...
.
...
This
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property
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has
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a
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default
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value
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"Foo".
...
This
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value
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will
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be
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injected
...
into
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the
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m_foo
...
field,
...
when
...
this
...
field
...
asks
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for
...
a
...
value.
...
A
...
property
...
with
...
a
...
field
...
attribute
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does
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not
...
need
...
to
...
declare
...
a
...
type
...
(the
...
type
...
can
...
be
...
discovered
...
by
...
analyzing
...
the
...
implementation
...
class).
...
The
...
implementation
...
class
...
set
...
a
...
new
...
value
...
to
...
the
...
m_foo
...
field
...
in
...
the
...
code.
...
When
...
this
...
action
...
occurs,
...
the
...
service
...
publication
...
is
...
updated.
...
If
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a
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published
...
property
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value
...
becomes
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null
...
,
...
the
...
property
...
is
...
unpublished
...
since
...
it
...
has
...
a
...
new
...
value.
...
You
...
can
...
also
...
publish
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'static'
...
properties
...
(not
...
attached
...
to
...
a
...
field):
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} @Component @Provides(properties= { @StaticServiceProperty(name="static", type="java.lang.String", value="this is a static property") }) public class FooProviderType1 implements FooService { @ServiceProperty(name="foo", value="Foo") private String m_foo; public void foo() { System.out.println("foo " + m_foo); m_foo = "bar"; } } {code} |
The
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second
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property
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(
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Static
...
)
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is
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published
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as
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a
...
static
...
property.
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This
...
property
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is
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not
...
attached
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to
...
a
...
field,
...
so,
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we
...
need
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to
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declare
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the
...
property
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type.
...
All
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primitive
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types
...
or
...
objects
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can
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be
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used
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has
...
property
...
type
...
(for
...
object,
...
the
...
qualified
...
name
...
of
...
the
...
class
...
is
...
used
...
as
...
java.lang.String).
...
In
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XML,
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this
...
can
...
also
...
be
...
done:
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{code:xml} <component classname="...FooProviderType1"> <provides> <property name="foo" field="m_foo" value="Foo"/> <property name="static" type="java.lang.String" value="this is a static property"/> </provides> </component> {code} |
Properties
...
may
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have
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a
...
default
...
value
...
(set
...
using
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the
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value
...
attribute).
...
This
...
value
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will
...
be
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used
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as
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initial
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value.
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The
...
value
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can
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be
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given
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in
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the
...
instance
...
configuration.
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The
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default
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value
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will
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be
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overridden
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in
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this
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case:
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{code:xml} <instance component="...FooProviderType1"> <property name="foo" value="My New Foo Value"/> <property name="static" value="My Value For Static"/> </instance> {code} |
Properties
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can
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also
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be
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'mandatory'.
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Mandatories
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properties
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must
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receive
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a
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value
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from
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the
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instance
...
configuration.
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If
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the
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instance
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configuration
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forgets
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a
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mandatory
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properties,
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the
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configuration
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is
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rejected.
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Mandatory
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attribute
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let
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you
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be
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sure
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to
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receive
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the
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complete
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set
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of
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initialization
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values:
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} @Component @Provides public class MyComponent implements MyService { @ServiceProperty(name="username", mandatory=true) private String m_username; @Property(name="password", mandatory=true) private String m_password; //... } {code} |
For
...
the
...
previous
...
components:
...
(name=myname,
...
password=****)
...
- is
...
- a
...
- valid
...
- configuration
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(password=****)
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- is
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- an
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- invalid
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- configuration
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- that
...
- will
...
- be
...
- rejected
...
- by iPOJO
Advanced features
Service Serving & Object Creation
When a consumer requires the published service, the handler sends an object (from the component class) of the implementation class. By default, it is always the same POJO object. If no objects already exists, an instance is created.
However, the handler supports the OSGi Service Factory. In this case, for each requester bundle, the handler sends a new object. To activate this policy, add the strategy attribute in the provides element:
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iPOJO h2. Advanced features h3. Service Serving & Object Creation When a consumer requires the published service, the handler sends an object (form the component class) of the implementation class. By default, it is always the same POJO object. If no objects already exists, an instance is created. However, the handler supports the OSGi _Service Factory_. In this case, for each requester bundle, the handler sends a new object. To activate this policy, add the {{strategy}} attribute in the {{provides}} element: {code} @Component @Provides(strategy="SERVICE") public class MyComponent implements MyService { //... } {code} |
or:
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{code:xml} <provides strategy="SERVICE"/> {code} |
Other
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strategies
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are
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available:
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strategy="instance"
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- allows
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- creating
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- one
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- service
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- object
...
- per
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- iPOJO
...
- instance using the service
- it is possible to create your own creation strategy by extending the
org.apache.felix.ipojo.handlers.providedservice.CreationStrategy
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- class
...
- and
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- by
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- indicating
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- the
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- qualified
...
- class
...
- name
...
- in
...
- the
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strategy
...
- attribute:
...
Code Block
...
@Component @Provides(strategy="org.acme.foo.MyCreationStrategy") public class MyComponent implements MyService { //... }
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Providing Several Services (XML
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only)
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In
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XML,
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you
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can
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declare
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several
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provides
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inside
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the
...
same
...
component.
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All those provided services will be managed individually, so will be published using several publication (i.e. org.osgi.frameowrk.ServiceRegistration). This case is useful when service properties are different for the different services.
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this provided service will be manage by the same handler but separately. Several services will be published (with different service registrations). This case is useful when service properties are different for the different services. {code:xml} <component classname="...FooProviderType1"> <provides specifications="...Foo"/> <provides specifications="...Bar"> <property name="foo" value="baz"/> </provides> </component> {code} !ps-foobar2.png! h3. Service Property Propagation The configuration handler has the possibility to propagate received properties to service publication. So, when the propagation is activated (on the {{properties}} element or on the {{@Component}} annotation), all properties received by the configuration handler will be propagated to all published service. If some properties are mapped on methods, these methods are invoked with the new value in argument. !ps-propagation.png! If an instance configuration contains properties starting with {{service.}}, they are automatically propagated. In the following example, the {{service.pid}} is automatically propagated. {code:xml} |
Service Property Propagation
The configuration handler has the possibility to propagate received properties to service publication. So, when the propagation is activated (on the properties element or on the @Component annotation), all properties received by the configuration handler will be propagated to all published services. If some properties are mapped on methods, these methods are invoked with the new value in argument.
If an instance configuration contains properties starting with service., they are automatically propagated. In the following example, the service.pid is automatically propagated.
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<instance component="...">
<property name="service.pid" value="my.pid"/>
</instance>
{code}
h3. |
Instance reconfiguration
iPOJO supports instance reconfiguration. When an instance is dynamically reconfigured and if the instance published service properties, the values are updated with the new configuration. For example, let's take the following component.
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@Component
@Instantiate
@Provides
public class MyComponent implements MyService {
@ServiceProperty(name="prop", value="initial")
private String myProp;
//...
}
|
The previous code also declares an instance (created without any configuration). This instance registers MyService with the service property prop=initial. If this instance is reconfigured using a configuration like: {prop="my value"}, the published properties will be updated with the new value, so prop=my value.
Publishing an abstract or concrete class as a Service
It is also possible to expose an abstract or concrete class as a service. To to this, just specify the published class in the specifications attribute:
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Instance reconfiguration iPOJO supports instance reconfiguration. When an instance is dynamically reconfigured, if the new configuration updates property values, these value are taken into account (both for field, and service publication). If some of these properties have methods, these methods are invoked with the new value in argument. h3. Publishing abstract and concrete class as services It is also possible to expose concrete and abstract class as services. To to this, just specify the published class in the {{specifications}} attribute: {code} @Component @Provides(specifications={...MyComponent}MyComponent.class) public class MyComponent { // ... } {code} |
or
...
in
...
XML:
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{code:xml} <component classname="...FooProviderType1"> <provides specifications="...AbstractFoo"/> </component> <component classname="...FooBarProviderType1"> <provides specifications="[...AbstractFoo, ...Bar]"/> </component> {code} |
As
...
illustrated
...
with
...
the
...
example
...
using
...
annotation,
...
the
...
component
...
can
...
also
...
publish
...
itself
...
as
...
a
...
service.
...
However,
...
such
...
practice
...
is not
...
recommended.
...
Controlling
...
the
...
service
...
exposition
...
from
...
the
...
implementation
...
class
...
To
...
control
...
the
...
exposition
...
of
...
the
...
published
...
service,
...
you
...
can
...
use
...
a
...
service
...
controller
...
.
...
A
...
service
...
controller
...
is
...
a
...
boolean
...
field
...
of
...
the
...
component
...
class.
...
The
...
injected
...
boolean
...
field
...
allows
...
the
...
code
...
to
...
impact
...
the
...
service
...
publication.
...
Setting
...
the
...
field
...
to
...
false
...
unregisters
...
the
...
service
...
from
...
the
...
service
...
registry.
...
Setting
...
it
...
back
...
to
...
true
...
re-publishes
...
the
...
service.
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{code:java} @Component @Provides public class ControllerCheckService implements FooService, CheckService { @ServiceController private boolean controller; // Service Controller public boolean foo() { return controller; } public boolean check() { System.out.println("Before : " + controller); controller = ! controller; // Change the publication System.out.println("After : " + controller); return controller; } } {code} |
Using
...
XML,
...
the
...
previous
...
component
...
description
...
is:
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{code:xml}
<component classname="org.apache.felix.ipojo.test.scenarios.component.controller.ControllerCheckService"
name="PS-Controller-1-default">
<provides>
<controller field="controller"/>
</provides>
</component>
|
The controller may have a value attribute setting the initial value. Setting this value to false disables the initial service registration:
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{code} The {{controller}} may have a value attribute setting the initial value. Setting this value to {{false}} disables the initial service registration: {code} @Component @Provides public class ControllerCheckService implements FooService, CheckService { @ServiceController(value=false) private boolean controller; // Service Controller public boolean foo() { return controller; } public boolean check() { System.out.println("Before : " + controller); controller = ! controller; // Change the publication System.out.println("After : " + controller); return controller; } } {code} |
If
...
several
...
interfaces
...
are
...
exposed,
...
the
...
controller
...
may
...
have
...
a
...
specification
...
attribute
...
indicating
...
the
...
impacted
...
service:
| Code Block |
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} @Component @Provides public class ControllerCheckService implements FooService, CheckService { @ServiceController(value=false, specification=FooService.class) private boolean controller; // Service Controller public boolean foo() { return controller; } public boolean check() { System.out.println("Before : " + controller); controller = ! controller; // Change the publication System.out.println("After : " + controller); return controller; } } {code} |
In
...
XML,
...
each
...
provides
...
can
...
have
...
one
...
controller
...
element.
| Code Block | ||||
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{code:xml} <component classname="org.apache.felix.ipojo.test.scenarios.component.controller.ControllerCheckService" name="PS-Controller-1-false"> <provides> <controller field="controller" value="false"/> </provides> </component> {code} h3. Being notified of the service registration and unregistration You can also be notified when the service is published and unpublished. This is done by specifying the two callbacks in the {{<provides/>}} element: {code:xml} |
Being notified of the service registration and unregistration
You can also be notified when the service is published and unpublished. This is done by specifying the two callbacks in the <provides/> element:
| Code Block | ||||
|---|---|---|---|---|
| ||||
<component
classname="org.apache.felix.ipojo.test.scenarios.component.callbacks.CallbacksCheckService"
name="PS-Callbacks-both-1">
<provides
specifications="org.apache.felix.ipojo.test.scenarios.ps.service.FooService"
post-unregistration="unregistered" post-registration="registered"/>
<provides
specifications="org.apache.felix.ipojo.test.scenarios.ps.service.CheckService"
post-unregistration="unregistered" post-registration="registered"/>
</component>
{code}
|
Or
...
by
...
using
...
the
...
@PostRegistration
...
and
...
@PostUnregistration
...
annotations:
| Code Block | ||||
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| ||||
{code:java} @PostRegistration public void registered(ServiceReference ref) { System.out.println("Registered"); } @PostUnregistration public void unregistered(ServiceReference ref) { System.out.println("Unregistered"); } {code} * The {{ |
- The
post-registration
...
- callback
...
- is
...
- called
...
- after
...
- the
...
- service
...
- publication
...
- The
post-unregistration
...
- callback
...
- is
...
- called
...
- after
...
- the
...
- service
...
- unpublication
...
Those
...
callback
...
methods
...
must
...
have
...
the
...
following
...
signature:
...
public
...
void
...
name(ServiceReference
...
ref)
...
.
...
So
...
they
...
receive
...
the
...
published
...
/
...
unpublished
...
service
...
reference.
...
The
...
callbacks
...
are
...
called
...
in
...
the
...
same
...
thread
...
as
...
the
...
publication
...
/
...
unpublication
...
itself.
...
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