SpringDM笔记18-Designing OSGi Enterprise Applications

1. Organizing OSGi components

    (1) ORGANIZING THE DEPENDENCIES

    The WAR Structure:

    ■ It’s a ZIP file
    ■ Downloadable resources (images, JavaScript files) are located at the root of the WAR
    ■ Application classes (servlet, web controllers) are located in WEB-INF/classes
    ■ Libraries and frameworks (packaged as JAR files) are in WEB-INF/lib

    Thanks to OSGi's sophisticated classloading mechanisms, OSGi supports this scenario out of the

    box:
    different versions of the same library can coexist in a container.

    (2) ORGANIZING THE APPLICATION

    Some guidelines for developing OSGi applications:

    ■ Separate the static components from the dynamic components:

    (1)Static components are bundles that define APIs by exporting interface-based Java packages.

    These bundles don’t contain a Spring application context (or a BundleActivator) and don’t register

    or reference any OSGi services.

    (2)Dynamic components are bundles that import Java packages from static bundles, provide

    implementations, and usually register OSGi services. As this is a Spring DM book, these bundles

    are Spring-powered.

    ■ Design Layered Application: （用SOA设计的思想设计）

    Perhaps exporting the packages of data access object (DAO) interfaces is useless, because what

    we’re really interested in is the business services. Remember, OSGi is sometimes referred to as

    a service-oriented architecture (SOA) in a JVM. We can still define the service API, but the  

    implementation can hide its inner workings. We can then reorganize our bundles in a simpler way

    and gather the service implementation and data access layer in the same bundle—the backend

    bundle.

2. Defining interactions between application bundles