关于headers的细节参见OSGi规范中的3.2节。一些OSGi实现框架可能会支持一些与众不同的jar包，但是这些jar包关于OSGi的格式还是不变的。
51CTO编辑推荐：OSGi入门与实践全攻略
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:
如果满足以下两个条件，Spring extender会通过一个bundle的具有"Spring-powered"的验证，当这个bundle启动时会为其创建一个相关联的application context：
The bundle classpath contains a folder META-INF/spring with one or more files in that folder with a '.xml' extension.
这个bundle的classpath包含一个目录META-INF/spring，这个目录中有一个或多个扩展名为'.xml'的文件。
META-INF/MANIFEST.MF contains a manifest header Spring-Context.
这个bundle中的META-INF/MANIFEST.MF文件包含一个名为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声明了可选header - SpringExtender-Version，那么extender将仅仅认可与之版本相符的指定版本约束的bundle（bundle的Bundle-Version）。SpringExtender-Version的值必须遵循OSGi规范3.2.5节中指定的版本范围。
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的情况下，spring extender仍然认为所有META-INF/spring中".xml"的文件都是spring的配置文件，所有的header都是默认值。
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就是根据这些文件(META-INF/spring中".xml"的文件)构造的。一个推荐的做法是将application context配置文件至少分割成2个文件，习惯上命名为 [模块名－context.xml] 和[模块名-osgi-context.xml]。modulename-context.xml文件包含了不依赖与OSGi相关的bean的定义（可以理解为普通bean定义）。modulename-osgi-context.xml文件则定义那些引入或输出OSGi服务的bean。这可能需要使用Spring Dynamic Modules的OSGi schema做为***命名空间，取代spring的'bean'命名空间，但这不是必须的。
以下是 Spring-Context的相关内容和配置，主要意思如下：
1.如果在Spring-Context指定了配置文件，那么extender将忽略 META-INF/spring 中的配置文件，除非明确指定。
2.可以用通配符，例如Spring-Context: osgi-*;
3.create-asynchronously=false（默认值是true） ，使用同步方式创建该bundle的application context。有一点需要注意，同步创建application context的过程是在OSGi的事件线程中进行的，它将阻塞这个线程的事件发送，直到完成application context的初始化。如果这个过程中发生了错误，那么将出现一个FrameworkEvent.ERROR，但是bundle的状态仍然还是ACTIVE。
4.wait-for-dependencies和timeout，从字面意思就能看出来了。
5.publish-context:=false（默认值是true)，不将application context作为一个服务发布。
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提供了很多现成的bundle，要使用Spring extender必须将这些bundle安装到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还提供了很多它自己的bundle，这些bundle可以直接被安装到OSGi平台中。要使用spring的***要求需要以下几个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.
以下几个bundle是spring的依赖bundle，可以在Spring Dynamic Modules的分发包中找到它们:
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.
这部份是关于OSGi平台MANIFEST中Import-Package和Export-Package的细节描述。
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