使用XML配置服务..（而不是属性）

Question

i have a ( bnd-annotated ) component that implements a simple api and exposes itself as a service

package com.mycompany.impl;
import com.mycompany.api.IFoo;

@Component(designateFactory=FooImpl.Configuration.class)
class FooImpl implements IFoo {

  interface Configuration {
    String foo();
    // ..
  }

  Configuration configuration;

  @Activate
  public void activate(Map properties) {
    configuration = Configurable.createConfigurable(Configuration.class, properties);
    // ..
  }

} 

its configuration is loaded from a watched directory by Felix FileInstall and the service is instantiated by the Felix Configuration Service ( at least, i assume thats whats happening - i'm new to OSGi, please bear with me ) This, with the generated MetaType descriptor is working great.

However, as it stands, FooImpl requires structured configuration ( lists of lists, maps of lists..etc ) and i was wondering if there is an elegant ( * ) way to configure instances of the component through a similar workflow; that is to say, configuration discovery and instantiation/deployment remains centralised.

It seems to me that the Configuration Service spec manages maps - will i have to roll my own Configuration Service & FileInstall to be able to present components with xml/json/yaml backed structured configuration?

• as opposed to, say, defining the location of an xml configuration file in properties ...confiception ? and doing my own parsing.

Answer 1

Yes and no...

The OSGi Configuration Admin service deals with abstract Configuration records, which are based on flat maps (actually java.util.Dictionary , but it's essentially the same thing). Config Admin does not know anything about the underlying physical storage; it always relies on somebody else to call the methods on the ConfigurationAdmin service, ie getConfiguration , createFactoryConfiguration etc.

The "somebody else" that calls Config Admin is usually called a "management agent". Felix FileInstall is a very simple example of a management agent that reads files in the Java properties format. Actually FileInstall is probably too simple and I don't consider it appropriate for production deployment — but that's a separate discussion.

It sounds like you want to write your own management agent that reads XML files and feeds them into Config Admin. This is really not a large or difficult task and you should not be afraid to take it on. Config Admin was designed under the assumption that applications would have very diverse requirements for configuration data storage, and that most applications would therefore have to write their own simple management agent, which is why it does not define its own storage format or location(s).

However, once the configuration data has been read by your management agent, it must be passed into Config Admin as a map/dictionary, which in turn will pass it to the components as a map. Therefore the components themselves do not receive highly structured data eg trees or nested maps. There is some flexibility though: configuration properties can contain lists of the based type; you can also use enum values etc.