使用服务组件运行时 [英] Using Service Component Runtime

问题描述

我的目标是从我的bundle中删除对OSGi的依赖。我使用felix（v 4.2.1）作为impl并运行它可嵌入。我安装 org.apache.felix.scr （v.6.6.2）bundle以获得Service Component Runtime支持。但是当我运行时

I goal is to remove dependencies on OSGi from my bundles. I use felix (v 4.2.1) as impl and run it embeddable. I install org.apache.felix.scr (v. 1.6.2) bundle to have Service Component Runtime support. But when I run

 ServiceReference ref = bundleContext().getServiceReference(ScrService.class.getName());
 ScrService s = (ScrService) bundleContext().getService(ref);

我得到 ClassCastException：org.apache.felix.scr.impl.ComponentRegistry无法转换为org.apache.felix.scr.ScrService 。

好的。我将修改系统包。

Okay. I will modify System Packages.

config.put(Constants.FRAMEWORK_SYSTEMPACKAGES, "org.apache.felix.scr");

现在我得到了

Caused by: org.osgi.framework.BundleException: Unresolved constraint in bundle org.apache.felix.scr [1]: Unable to resolve 1.0: missing requirement [1.0] osgi.wiring.package; (&(osgi.wiring.package=org.osgi.framework)(version>=1.4.0)(!(version>=2.0.0)))
        at org.apache.felix.framework.Felix.resolveBundleRevision(Felix.java:3974)
        at org.apache.felix.framework.Felix.startBundle(Felix.java:2037)
        at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:955)
        at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:942)
        at com.copyright.rup.communications.felix.Felix.addBundle(Felix.java:86)
        ... 28 more

我该如何解决？

推荐答案

我怀疑你试图获得 ScrService 的第一个区块已开启嵌入方（即在框架之外，而不是在已安装的软件包中）。

I suspect your first block where you try to get hold of ScrService is on the embedding side (i.e. outside of the framework, not from within an installed bundle).

如果是这种情况，那么你有两份 ScrService - 一个从嵌入代码的ClassLoader加载，一个由scr b的ClassLoader加载当框架解决了它时。这就是为什么你看到 ClassCastException 。

If this is the case, then you have two copies of the ScrService - one loaded from your embedding code's ClassLoader and one loaded by ClassLoader of the scr bundle when it's resolved by the framework. This is why you're seeing the ClassCastException.

你可以从框架中导出SCR包的导出捆绑。

You can just export what the SCR bundle's exports from the framework bundle.

OSGi核心规范v5 指出，如果模块同时具有相同包的导入和导出定义，则在捆绑连接的解析中，框架将首先尝试从外部解析，如果成功丢弃重叠的导出定义。

Section 3.8, page 51 of the OSGi Core spec v5 states that in resolution of bundle wiring if a module has both import and export definitions of the same package then the framework will first try to resolve externally and if successful discard the overlapping export definition.

所以将SCR运行时包的Export-Package清单头复制为框架属性：

So copy the SCR runtime bundle's Export-Package manifest header as a framework property:

properties.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA, 
        "org.ops4j.pax.url.mvn,org.apache.felix.scr;uses:=\"org.osgi.framework," +
        "org.osgi.service.component\";version=\"1.7\"," +
        "org.apache.felix.scr.component;status=provisional;mandatory:=status;" +
        "uses:=\"org.osgi.service.component\";version=\"1.0\"," +
        "org.osgi.service.component;uses:=\"org.osgi.framework\";version=\"1.2\"");

//Which you pass to the FrameworkFactory ...

ServiceLoader<FrameworkFactory> loader = ServiceLoader.load(FrameworkFactory.class);
Iterator<FrameworkFactory> iterator = loader.iterator();
Framework framework = iterator.next().newFramework(properties);
framework.start();

有几点需要注意：

• 如果您还没有使用 ConfigurationAdmin ，那么还要安装 org.osgi.compendium ，以确保您至少拥有<$ c $的API类c> org.osgi.service.cm。* 和 org.osgi.service.metatype * ，AFAIK这些是SCR运行时所必需的。

• If you're not already using ConfigurationAdmin, then also install org.osgi.compendium to ensure you have at least have the API classes for org.osgi.service.cm.* and org.osgi.service.metatype*, AFAIK these are necessary for the SCR runtime.

除非您认真定制实际框架，否则不应使用 Constants.FRAMEWORK_SYSTEMPACKAGES 您可能希望使用 Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA 来扩展框架包导出的内容。 （框架实现对于 FRAMEWORK_SYSTEMPACKAGES 具有非常好的默认值，并且在嵌入时通常不需要修改它。）

You shouldn't use Constants.FRAMEWORK_SYSTEMPACKAGES unless you're seriously customising the actual framework, instead you'd probably want to use Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA to extend what is exported by the framework bundle. (The framework implementations have pretty good defaults for FRAMEWORK_SYSTEMPACKAGES and it's normally unnecessary to modify this when embedding).

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