1. Configuration for registering services：The tag:service
(1)BEAN REFERENCE
Spring DM also supports the use of an anonymous bean(inner bean) within the service tag, as
shown in the following:
<osgi:service id="testService" interface="com.manning.sdmia.springdm.service.TestService">
<bean class="com.manning.sdmia.springdm.service.impl.TestServiceImpl"/>
</osgi:service>
其中，bean：TestServiceImpl无Id,不能在Spring配置文件中其他地方使用。
(2) SERVICE INTERFACE SUPPORT
Because OSGi allows you to register services under several identifiers, Spring DM also provides
an inner interfaces tag that accepts a list of values, as shown in the following:
<osgi:service id="testService" ref="testServiceBean">
<osgi:interfaces>
<value>
com.manning.sdmia.springdm.service.TestService
</value>
<value>(...)</value>
</osgi:interfaces>
</osgi:service>
In addition to this explicit configuration of interfaces, Spring DM provides a mechanism to detect
values used for the interface attribute and interfaces tag. This mechanism is configured through
the auto-export attribute and provides alternative strategies to autodetect interfaces when the
interface attribute and interfaces tag are not specified, as described follow:
■ disabled：Default strategy where you need to explicitly specify values of the interface
attribute and interfaces tag；
■ interfaces：Strategy using all the interfaces implemented by the service；
■ class-hierarchy：Strategy using the class and all parent classes of the service；
■ all-classes：Corresponds to both the interfaces and class-hierarchy strategies。
示例：
<osgi:service id="testService" ref="testServiceBean" auto-export="interfaces"/>
(3) SERVICE PROPERTY SUPPORT,使用service-properties标签：
<osgi:service id="testService" ref="testServiceBean"
interface="com.manning.sdmia.springdm.service.TestService">
<osgi:service-properties>
<entry key="creationDate" value="2009-12-12"/>
(...)
</osgi:service-properties>
</osgi:service>
(4)MANAGING THE CLASSLOADING CONTEXT
If TCCL specified in the service registration configuration , Spring DM makes it possible during the
service call to see all the classes of the bundle that registers the service,When exporting a bean
as an OSGi service, Spring DM allows you to specify which classes are reachable from this
service based on the TCCL managed by Spring DM. At this level, either no classes, or classes
present in the bundle that registers service, will be reachable.This behavior can be configured
using the context-class-loader attribute of the service tag. For example:
<osgi:service id="testService" ref="testServiceBean"
interface="com.manning.sdmia.springdm.service.TestService"
context-class-loader="service-provider"/>
Context classloading strategies for the context-class-loader attribute:
■ unmanaged:This is the default strategy, where no context classloader management is done.
■ service-provider:This strategy allows the service implementation, during the service call, to
see all the classes of the bundle that registered the service.
(5)SERVICE-RANKING SUPPORT
Spring DM allows you to specify a rank for a service through the service tag’s ranking attribute.
This attribute is optional and its default value is 0. The following snippet shows how to use this
attribute:
<osgi:service id="testService" ref="testServiceBean"
interface="com.manning.sdmia.springdm.service.TestService" ranking="5" />
OSGi’s ranking feature is used when you’re trying to obtain a service reference and there’s more
than one service match. In this situation, the service with the highest ranking will match. The
ranking of services is also used by Spring DM as a tiebreaker in its shutdown algorithm.
(6)BUNDLE SCOPE
SpringDM提供了一个Bean Scope:bundle,而OSGi 规范也规定了一个借口：ServiceFactory，用于针对特定
的服务请求创建每个Bundle的服务实例；SpringDM实现这种机制没有使用OSGi规范中ServiceFactory接口，
而是使用bundle Scpoe来实现.
The configuration of the service factory feature using bundle scope must be done on the bean (in
the bean tag) in order to export the bean as a service. It is not done on the service exporter (the
service tag of the osgi namespace). The following snippet shows this:
<osgi:service id="testService" ref="testServiceBean"
interface="com.manning.sdmia.springdm.service.TestService"/>
<bean id=" testServiceBean" scope="bundle"
class="com.manning.sdmia.springdm.service.impl.TestServiceImpl">
(...)
</bean>
2. Configuration for referencing services(using a single service.)
(1)SERVICE INTERFACE SUPPORT
<osgi:reference id="testService">
<osgi:interfaces>
<value>
com.manning.sdmia.springdm.service.TestService
</value>
<value>(...)</value>
</osgi:interfaces>
</osgi:reference>
(2)SERVICE AVAILABILITY IN REFERENCING
The availability attribute of the reference tag allows you to configure whether or not service is
optional, and it accepts the values listed follow:
Values for the availability attribute：
■ optional:This value specifies that the service is optional and doesn’t need to be available all
the time.
■ mandatory:This is the default value, which specifies that the service is mandatory for the
component to function correctly. The service must always be present for the component’s
execution.
注意：Before Spring DM version 2, the availability attribute was named cardinality . In that
context, the value 0..1 was the equivalent of the optional value, and 1.. was the equivalent
of mandatory.
Setting the value for the availability attribute specifies how Spring DM should behave during
service matching and, more particularly, when the service can’t be immediately resolved.
Different behaviors of Spring DM depending on service availability ：
■ On Spring container startup
Availability：mandatory
Description：The container waits until the service is available before completing its startup.
If the service isn’t available after the specified timeout, the container throws a
ServiceUnavailableException exception and the container isn’t started.
Availability：optional
Description：The container starts even if the referenced service isn’t available.
■ Spring container started
Availability：mandatory
Description：On a service call, if the service isn’t available, the container waits until the service
becomes available to execute the call. If the service isn’t available after the specified timeout,
the container throws a ServiceUnavailableException exception.
Availability：mandatory
Description：It behaves in the same way as on Spring container startup.
示例：
<osgi:reference id="testService" interface="com.manning.sdmia.springdm.service.TestService"
availability="optional" />
<osgi:reference id="testService" interface="com.manning.sdmia.springdm.service.TestService"
timeout="1000" depends-on="anotherBean"/>
(3)CLASSLOADER MANAGEMENT
As with service exporting, Spring DM provides support to automatically manage the TCCL when
calling a referenced service. Spring DM allows a service call invocation to see all the classes of
the calling bundle, or of the bundle that registered the service, through the setting of the TCCL.
When referencing an OSGi service, Spring DM allows you to specify which classes are reachable
from this service by setting the context classloader. At this level, either no classes, or classes
present in the bundle that either registers or calls the service, will be reachable.
The class visibility can be configured using the context-class-loader attribute of the service tag.
<osgi:reference id="testService" interface="com.manning.sdmia.springdm.service.TestService"
context-class-loader="service-provider" />
Context classloading strategies for the context-class-loader attribute :
■ Strategy:client
Description:This default strategy allows the implementation to see all the classes of the calling
component during the service call.
■ Strategy: service-provider
Description:This strategy allows the service implementation to see all the classes of the bundle
that registered the service during its call.
■ Strategy:unmanaged
Description:This strategy performs no context classloader management.
注意：Classloader management for services can be configured both when registering and
referencing services. Spring DM will always override the reference setting if the service setting
is configured.
(4)SERVICE SELECTION
Spring DM allows you to specify fine-grained selection of services at the level of the reference
element. Two attributes are available:
■ filter: can be used as an expression to select a subset of services to be matched.
■ bean-name: allows you to select the service with the bean-name property set. For this to work,
the service must have been registered using Spring DM or a tool that also uses the bean-name
property.
The following snippet shows how to select the service corresponding to the TestService interface
and having a creationDate attribute with the value 2009-12-12:
<osgi:reference id="testService" interface="com.manning.sdmia.springdm.service.TestService"
filter="(creationDate='2009-12-12')"/>.