Package org.apache.felix.dm.annotation.api

Annotation Type ConfigurationDependency

@Retention(CLASS) @Target(METHOD) public @interface ConfigurationDependency
Annotates a method for injecting a Configuration Dependency.

A configuration dependency is required by default, and allows you to depend on the availability of a valid configuration for your component. This dependency requires the OSGi Configuration Admin Service. Configuration Dependency callback is always invoked before any service dependency callbacks, and before init/start callbacks. The annotation can be applied on a callback method which accepts the following parameters:

  • callback(Dictionary)
  • callback(Component, Dictionary)
  • callback(Component, Configuration ... configTypes) // type safe configuration interface(s)
  • callback(Configuration ... configTypes) // type safe configuration interface(s)
  • callback(Dictionary, Configuration ... configTypes) // type safe configuration interfaces(s)
  • callback(Component, Dictionary, Configuration ... configTypes) // type safe configuration interfaces(s)

Usage Examples

In the following example, the Printer components depends on a configuration whose PID name is "sample.Printer". This service will initialize its ip/port number from the provided configuration. 


 package sample;
 
 @Component
 public class Printer {
     @ConfigurationDependency(propagate=true) // Will use the fqdn of the  Printer interface as the pid.
     void updated(Dictionary cnf) {
         if (cnf != null) {
             String ip = cnf.get("address");
             int port = Integer.parseInt(cnf.get("port"));
         }
     }
 }
You can also define your own component properties using a custom type-safe interface: 
 package sample;
 
 interface PrinterConfig {
     String getAddress();       
     int getPort();
 }
Next, we define our Printer service which depends on the PrinterConfig: 
 package sample;

 @Component
 public class Printer {
     @ConfigurationDependency // Will use the fqdn of the  PrinterConfig interface as the pid.
     void updated(PrinterConfig cnf) {
         if (cnf != null) {
             String ip = cnf.getAddress();
             int port = cnf.getPort();
         }
     }
 }
In the above example, the updated callback accepts a type-safe configuration type (and its fqdn is used as the pid).

Configuration type is a new feature that allows you to specify an interface that is implemented by DM and such interface is then injected to your callback instead of the actual Dictionary. Using such configuration interface provides a way for creating type-safe configurations from a actual Dictionary that is normally injected by Dependency Manager. The callback accepts in argument an interface that you have to provide, and DM will inject a proxy that converts method calls from your configuration-type to lookups in the actual map or dictionary. The results of these lookups are then converted to the expected return type of the invoked configuration method.
As proxies are injected, no implementations of the desired configuration-type are necessary!

The lookups performed are based on the name of the method called on the configuration type. The method names are "mangled" to the following form: [lower case letter] [any valid character]*. Method names starting with get or is (JavaBean convention) are stripped from these prefixes. For example: given a dictionary with the key "foo" can be accessed from a configuration-type using the following method names: foo(), getFoo() and isFoo().

If the property contains a dot (which is invalid in java method names), then dots (".") can be converted using the following conventions:

  • if the method name follows the javabean convention and/or kamel casing convention, then each capital letter is assumed to map to a "dot", followed by the same letter in lower case. This means only lower case properties are supported in this case. Example: getFooBar() or fooBar() will map to "foo.bar" property.
  • else, if the method name follows the standard OSGi metatype specification, then dots are encoded as "_"; and "_" is encoded as "__". (see OSGi r6 compendium, chapter 105.9.2). Example: "foo_BAR()" is mapped to "foo.BAR" property; "foo__BAR_zoo()" is mapped to "foo_BAR.zoo" property.

The return values supported are: primitive types (or their object wrappers), strings, enums, arrays of primitives/strings, Collection types, Map types, Classes and interfaces. When an interface is returned, it is treated equally to a configuration type, that is, it is returned as a proxy.

Arrays can be represented either as comma-separated values, optionally enclosed in square brackets. For example: [ a, b, c ] and a, b,c are both considered an array of length 3 with the values "a", "b" and "c". Alternatively, you can append the array index to the key in the dictionary to obtain the same: a dictionary with "arr.0" => "a", "arr.1" => "b", "arr.2" => "c" would result in the same array as the earlier examples.

Maps can be represented as single string values similarly as arrays, each value consisting of both the key and value separated by a dot. Optionally, the value can be enclosed in curly brackets. Similar to array, you can use the same dot notation using the keys. For example, a dictionary with 

"map" => "{key1.value1, key2.value2}"
and a dictionary with 
"map.key1" => "value1", "map2.key2" => "value2"
result in the same map being returned. Instead of a map, you could also define an interface with the methods getKey1() and getKey2 and use that interface as return type instead of a Map.

In case a lookup does not yield a value from the underlying map or dictionary, the following rules are applied:

  1. primitive types yield their default value, as defined by the Java Specification;
  2. string, Classes and enum values yield null;
  3. for arrays, collections and maps, an empty array/collection/map is returned;
  4. for other interface types that are treated as configuration type a null-object is returned.
Author:
Felix Project Team

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    String
    name
    The name for this configuration dependency.
    String
    pid
    Returns the pid for a given service (by default, the pid is the service class name, of the FQDN of the configuration type found in the updated callback signature.
    Class<?>
    pidClass
    Returns the pid from a class name.
    boolean
    propagate
    Returns true if the configuration properties must be published along with the service.
    boolean
    required
    Sets the required flag which determines if this configuration dependency is required or not.

  • Element Details

    • pid

      String pid
      Returns the pid for a given service (by default, the pid is the service class name, of the FQDN of the configuration type found in the updated callback signature.
      Returns:
      the pid for a given service (default = Service class name)
      Default:
      ""

    • pidClass

      Class<?> pidClass
      Returns the pid from a class name. The full class name will be used as the configuration PID.
      Returns:
      the pid class whose FQDN name is used as the configuration PID.
      Default:
      java.lang.Object.class

    • propagate

      boolean propagate
      Returns true if the configuration properties must be published along with the service. Any additional service properties specified directly are merged with these. The configuration dependency properties take precedence over the component service properties, meaning that a given configuration property will override the same property that is already present in the component service properties.
      Returns:
      true if configuration must be published along with the service, false if not.
      Default:
      false

    • required

      boolean required
      Sets the required flag which determines if this configuration dependency is required or not. A configuration dependency is required by default.
      Returns:
      this service dependency
      Default:
      true

    • name

      String name
      The name for this configuration dependency. When you give a name a dependency, it won't be evaluated immediately, but after the component's init method has been called, and from the init method, you can then return a map in order to dynamically configure the configuration dependency (the map has to contain a "pid" and/or "propagate" flag, prefixed with the dependency name). Then the dependency will be evaluated after the component init method, and will be injected before the start method.

      Usage example of a Configuration dependency whose pid and propagate flag is configured dynamically from init method: 

        /**
    * A Service that dynamically defines an extra dynamic configuration dependency from its init method. 
    */
  @Component
  class X {
      private Dictionary m_config;
      
      // Inject initial Configuration (injected before any other required dependencies)
      @ConfigurationDependency
      void componentConfiguration(Dictionary config) {
           // you must throw an exception if the configuration is not valid
           m_config = config;
      }
      
      /**
       * All unnamed dependencies are injected: we can now configure our dynamic configuration whose dependency name is "global".
       */
      @Init
      Map init() {
          return new HashMap() {{
              put("global.pid", m_config.get("globalConfig.pid"));
              put("global.propagate", m_config.get("globalConfig.propagate"));
          }};
      } 
 
      // Injected after init, and dynamically configured by the init method.
      @ConfigurationDependency(name="global")
      void globalConfiguration(Dictionary globalConfig) {
           // you must throw an exception if the configuration is not valid
      }
 
      /**
       * All dependencies are injected and our service is now ready to be published.
       */
      @Start
      void start() {
      }
  }
      Returns:
      the dependency name used to configure the dependency dynamically from init callback
      Default:
      ""