關於headers的細節參見OSGi規范中的3.2節。一些OSGi實現框架可能會支持一些與眾不同的jar包，但 是這些jar包關於OSGi的格式還是不變的。
The Spring extender recognizes a bundle as "Spring-powered" and will create an associated application context when the bundle is started if one or both of the following conditions is true:
如果滿足以下兩個條件，Spring extender會通過一個bundle的具有"Spring-powered"的驗證，當這個 bundle啟動時會為其創建一個相關聯的application context：
The bundle classpath contains a folder META-INF/spring with one or more files in that folder with a '.xml' extension.
這個bundle的classpath包含一個目錄META-INF/spring，這個目錄中有一個或多個擴展名為'.xml'的 文件。
META-INF/MANIFEST.MF contains a manifest header Spring-Context.
這個bundle中的META-INF/MANIFEST.MF文件包含一個名為Spring-Context的header。
In addition, if the optional SpringExtender-Version header is declared in the bundle manifest, then the extender will only recognize bundles where the specified version constraints are satisfied by the version of the extender bundle (Bundle-Version). The value of the SpringExtender-Version header must follow the syntax for a version range as specified in section 3.2.5 of the OSGi Service Platform Core Specification.
另外，如果bundle的manifest聲明了可選header - SpringExtender-Version，那麼extender將僅僅認 可與之版本相符的指定版本約束的bundle（bundle的Bundle-Version）。SpringExtender-Version的值必 須遵循OSGi規范3.2.5節中指定的版本范圍。
In the absence of the Spring-Context header the extender expects every ".xml" file in the META-INF/spring folder to be a valid Spring configuration file, and all directives (see below) take on their default values.
在缺少Spring-Context的情況下，spring extender仍然認為所有META-INF/spring中".xml"的文件都 是spring的配置文件，所有的header都是默認值。
An application context is constructed from this set of files. A suggested practice is to split the application context configuration into at least two files, named by convention modulename-context.xml and modulename-osgi-context.xml. The modulename-context.xml file contains regular bean definitions independent of any knowledge of OSGi. The modulename-osgi -context.xml file contains the bean definitions for importing and exporting OSGi services. It may (but is not required to) use the Spring Dynamic Modules OSGi schema as the top-level namespace instead of the Spring 'beans' namespace.
application context就是根據這些文件(META-INF/spring中".xml"的文件)構造的。一個推薦的做法 是將application context配置文件至少分割成2個文件，習慣上命名為 [模塊名－context.xml] 和[模塊 名-osgi-context.xml]。modulename-context.xml文件包含了不依賴與OSGi相關的bean的定義（可以理解 為普通bean定義）。modulename-osgi-context.xml文件則定義那些引入或輸出OSGi服務的bean。這可能 需要使用Spring Dynamic Modules的OSGi schema做為頂級命名空間，取代spring的'bean'命名空間，但 這不是必須的。
以下是 Spring-Context的相關內容和配置，主要意思如下：
1.如果在Spring-Context指定了配置文件，那麼extender將忽略 META-INF/spring 中的配置文件，除 非明確指定。
2.可以用通配符，例如Spring-Context: osgi-*;
3.create-asynchronously=false（默認值是true） ，使用同步方式創建該bundle的application context。有一點需要注意，同步創建application context的過程是在OSGi的事件線程中進行的，它將阻 塞這個線程的事件發送，直到完成application context的初始化。如果這個過程中發生了錯誤，那麼將 出現一個FrameworkEvent.ERROR，但是bundle的狀態仍然還是ACTIVE。
4.wait-for-dependencies和timeout，從字面意思就能看出來了。
5.publish-context:=false（默認值是true)，不將application context作為一個服務發布。
The Spring-Context manifest header may be used to specify an alternate set of configuration files. The resource paths are treated as relative resource paths and resolve to entries defined in the bundle and the set of attached fragments. When the Spring-Context header defines at least one configuration file location, any files in META-INF/spring are ignored unless directly referenced from the Spring-Context header.
The syntax for the Spring-Context header value is:
Spring-Context-Value ::= context ( ',' context ) * context ::= path ( ';' path ) * (';' directive) *
This syntax is consistent with the OSGi Service Platform common header syntax defined in section 3.2.3 of the OSGi Service Platform Core Specification.
For example, the manifest entry:
Spring-Context: config/account-data-context.xml, config/account-security-context.xml
will cause an application context to be instantiated using the configuration found in the files account-data-context.xml and account-security-context.xml in the bundle jar file.
A number of directives are available for use with the Spring-Context header. These directives are:
create-asynchronously (false|true): controls whether the application context is created asynchronously (the default), or synchronously.
For example:
Spring-Context: *;create-asynchronously=false
Creates an application context synchronously, using all of the "*.xml" files contained in the META-INF/spring folder.
Spring-Context: config/account-data-context.xml;create-asynchrously:=false
Creates an application context synchronously using the config/account-data-context.xml configuration file. Care must be taken when specifying synchronous context creation as the application context will be created on the OSGi event thread, blocking further event delivery until the context is fully initialized. If an error occurs during the synchronous creation of the application context then a FrameworkEvent.ERROR event is raised. The bundle will still proceed to the ACTIVE state.
wait-for-dependencies (true|false): controls whether or not application context creation should wait for any mandatory service dependencies to be satisfied before proceeding (the default), or proceed immediately without waiting if dependencies are not satisfied upon startup.
For example:
Spring-Context: config/osgi-*.xml;wait-for-dependencies:=false
Creates an application context using all the files matching "osgi-*.xml" in the config directory. Context creation will begin immediately even if dependencies are not satisfied. This essentially means that mandatory service references are treated as though they were optional - clients will be injected with a service object that may not be backed by an actual service in the registry initially. See section 4.2 for more details.
timeout (300): the time to wait (in seconds) for mandatory dependencies to be satisfied before giving up and failing application context creation. This setting is ignored if wait- for-dependencies:=false is specified. The default is 5 minutes (300 seconds).
For example:
Spring-Context: *;timeout:=60
publish-context (true|false): controls whether or not the application context object itself should be published in the OSGi service registry. The default is to publish the context.
For example:
Spring-Context: *;publish-context:=false
If there is no Spring-Context manifest entry, or no value is specified for a given directive in that entry, then the directive takes on its default value.
3.2 Required Spring Framework and Spring Dynamic Modules Bundles
The Spring Dynamic Modules project provides an number of bundle artifacts that must be installed in your OSGi platform in order for the Spring extender to function correctly:
Spring Dynamic Modules提供了很多現成的bundle，要使用Spring extender必須將這些bundle安裝到 OSGi平台中:
The extender bundle itself, org.springframework.osgi.extender
The core implementation bundle for the Spring Dynamic Modules support, org.springframework.osgi.core
The Spring Dynamic Modules i/o support library bundle, ' org.springframework.osgi.io
In addition the Spring Framework provides a number of bundles that are required to be installed. As of release 2.5 of the Spring Framework, the Spring jars included in the Spring distribution are valid OSGi bundles and can be installed directly into an OSGi platform. The minimum required set of bundles is:
另外spring還提供了很多它自己的bundle，這些bundle可以直接被安裝到OSGi平台中。要使用spring 的最低要求需要以下幾個bundle:
spring-core.jar (bundle symbolic name org.springframework.core)
spring-context.jar (bundle symbolic name org.springframework.context)
spring-beans.jar (bundle symbolic name org.springframework.beans)
spring-aop.jar (bundle symbolic name org.springframework.aop)
In additional the following supporting library bundles are required. OSGi-ready versions of these libraries are shipped with the Spring Dynamic Modules distribution.
以下幾個bundle是spring的依賴bundle，可以在Spring Dynamic Modules的分發包中找到它們:
aopalliance
backport-util (for JDK 1.4)
cglib-nodep
commons-logging (SLF4J version highly recommended)
3.3 Importing and Exporting packages
Refer to the OSGi Service Platform for details of the Import-Package and Export-Package manifest headers. Your bundle will need an Import-Package entry for every external package that the bundle depends on. If your bundle provides types that other bundles need access to, you will need Export-Package entries for every package that should be available from outside of the bundle.
這部份是關於OSGi平台MANIFEST中Import-Package和Export-Package的細節描述。
