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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
...
provide
...
a
...
service,
...
the
...
implementation
...
class
...
MUST
...
implement
...
the
...
service
...
interface.
...
In
...
XML,
...
to
...
provide
...
the
...
service,
...
the
...
component
...
type
...
needs
...
to
...
contain
...
the
...
<provides/>
...
element:
Code Block | ||||
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| ||||
{code:xml} <component className="...FooProviderType1"> <provides/> </component> {code} !ps-foo.png! The {{<provides/>}} or {{@Provides}} suffice to declare that each instance of this type will provide the FooService (for more info about instances see [FELIX: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. 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 /> </component> |
The <provides/>
or @Provides
suffice to declare that each instance of this type will provide 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:
Code Block |
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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 |
Info | ||
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}
In the 1.0.0 version and before, the {{
attribute was named {{
. |
Info | ||
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If you use the |
Info | ||
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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:
Code Block |
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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
...
XML,
...
it
...
gives:
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{code:xml} <component classname="...FooProviderType1"> <provides> <property name="foo" field="m_foo" value="Foo"/> </provides> </component> {code} |
The
...
declared
...
property
...
is
...
attached
...
to
...
the
...
m_foo
...
field.
...
This
...
property
...
is
...
published
...
with
...
the
...
name
...
foo
...
.
...
This
...
property
...
has
...
a
...
default
...
value
...
"Foo".
...
This
...
value
...
will
...
be
...
injected
...
into
...
the
...
m_foo
...
field,
...
when
...
this
...
field
...
asks
...
for
...
a
...
value.
...
A
...
property
...
with
...
a
...
field
...
attribute
...
does
...
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
...
a
...
published
...
property
...
value
...
becomes
...
null
...
,
...
the
...
property
...
is
...
unpublished
...
since
...
it
...
has
...
a
...
new
...
value.
...
You
...
can
...
also
...
publish
...
'static'
...
properties
...
(not
...
attached
...
to
...
a
...
field):
Code Block |
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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
...
second
...
property
...
(
...
Static
...
)
...
is
...
published
...
as
...
a
...
static
...
property.
...
This
...
property
...
is
...
not
...
attached
...
to
...
a
...
field,
...
so,
...
we
...
need
...
to
...
declare
...
the
...
property
...
type.
...
All
...
primitive
...
types
...
or
...
objects
...
can
...
be
...
used
...
has
...
property
...
type
...
(for
...
object,
...
the
...
qualified
...
name
...
of
...
the
...
class
...
is
...
used
...
as
...
java.lang.String).
...
In
...
XML,
...
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
...
have
...
a
...
default
...
value
...
(set
...
using
...
the
...
value
...
attribute).
...
This
...
value
...
will
...
be
...
used
...
as
...
initial
...
value.
...
The
...
value
...
can
...
be
...
given
...
in
...
the
...
instance
...
configuration.
...
The
...
default
...
value
...
will
...
be
...
overridden
...
in
...
this
...
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
...
can
...
also
...
be
...
'mandatory'.
...
Mandatories
...
properties
...
must
...
receive
...
a
...
value
...
from
...
the
...
instance
...
configuration.
...
If
...
the
...
instance
...
configuration
...
forgets
...
a
...
mandatory
...
properties,
...
the
...
configuration
...
is
...
rejected.
...
Mandatory
...
attribute
...
let
...
you
...
be
...
sure
...
to
...
receive
...
the
...
complete
...
set
...
of
...
initialization
...
values:
Code Block |
---|
} @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
...
(password=****)
...
- is
...
- an
...
- invalid
...
- configuration
...
- 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:
Code Block |
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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 (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: {code} @Component @Provides(strategy="SERVICE") public class MyComponent implements MyService { //... } {code} |
or:
Code Block | ||||
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| ||||
{code:xml} <provides strategy="SERVICE"/> {code} |
Other
...
strategies
...
are
...
available:
...
strategy="instance"
...
- allows
...
- creating
...
- one
...
- service
...
- object
...
- per
...
- iPOJO
...
- instance
...
- using
...
- the
...
- service
...
- it
...
- is
...
- possible
...
- to
...
- create
...
- your
...
- own
...
- creation
...
- strategy
...
- by
...
- extending
...
- the
...
org.apache.felix.ipojo.handlers.providedservice.CreationStrategy
...
- class
...
- and
...
- by
...
- indicating
...
- the
...
- qualified
...
- class
...
- name
...
- in
...
- the
...
strategy
...
- attribute:
...
Code Block
...
@Component @Provides(strategy="org.acme.foo.MyCreationStrategy") public class MyComponent implements MyService { //... }
...
Providing Several Services (XML
...
only)
...
In
...
XML,
...
you
...
can
...
declare
...
several
...
provides
...
inside
...
the
...
same
...
component.
...
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.
Code Block | ||||
---|---|---|---|---|
| ||||
{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 services. 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.
Code Block | ||||
---|---|---|---|---|
| ||||
<instance component="...">
<property name="service.pid" value="my.pid"/>
</instance>
{code}
h3. Instance reconfiguration
|
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.
Code Block | ||||
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| ||||
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. {code:java} @Component @Instantiate @Provides public class MyComponent implements MyService { @ServiceProperty(name="prop", value="initial") private String myProp; //... } {code} |
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:
Code Block |
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}}. h3. 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: {code} @Component @Provides(specifications=MyComponent.class) public class MyComponent { // ... } {code} |
or
...
in
...
XML:
Code Block | ||||
---|---|---|---|---|
| ||||
{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.
Code Block | ||||
---|---|---|---|---|
| ||||
{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:
Code Block | ||||
---|---|---|---|---|
| ||||
{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:
Code Block |
---|
{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 |
---|
} @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 | ||||
---|---|---|---|---|
| ||||
{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 | ||||
---|---|---|---|---|
| ||||
{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.
...
Include Page | ||||
---|---|---|---|---|
|
...