DependencyResolver

Helper class for resolving component dependencies.

Implements: IReferenceable, IReconfigurable

Description

The DependencyResolver is a helper class that allows you to resolve component dependencies. It is configured to resolve named dependencies by a specific locator.

Important points:

  • During deployment the dependency locator can be changed. This mechanism can be used to clarify a specific dependency among several alternatives. Typically components are configured to retrieve the first dependency that matches a logical group, type and version. However, if the container contains more than one instance and the resolution has to be specific about those instances, they can be given a unique name and the dependency resolvers can be reconfigured to retrieve dependencies according to their name.

Configuration parameters

  • dependencies:
    • [dependency name 1]: Dependency 1 locator (descriptor)
    • …
    • [dependency name N]: Dependency N locator (descriptor)

References

References must match configured dependencies.

Constructors

Creates a new instance of the dependency resolver.

public DependencyResolver(ConfigParams config)

  • config: ConfigParams - (optional) default configuration where key the is dependency name and value is the locator (descriptor)

Instance methods

configure

Configures the component with specified parameters.

publicvoid configure(ConfigParams config) throws ConfigException

find

Finds all matching dependencies by their name.

public Object find(String name)

  • name: String - name the name of the dependency to locate.
  • returns: Object - the dependency locator or null if locator was not configured.

getOneOptional

Gets one optional dependency by its name.

public Object getOneOptional(String name)

  • name: String - dependency name to locate.
  • returns: Object - dependency reference or null if the dependency was not found.

getOneRequired

Gets one required dependency by its name. At least one dependency must present. If the dependency was found it throws a ReferenceException.

public Object getOneRequired(String name) throws ReferenceException

  • name: String - dependency name to locate.
  • returns: Object - dependency reference

getOptional

Gets all optional dependencies by their name.

public List getOptional(String name)

  • name: String - dependency name to locate.
  • returns: List - list with found dependencies or empty list of no dependencies was found.

    getRequired

    Gets all required dependencies by their name. At least one dependency must be present. If no dependency was found, it throws a ReferenceException

    public List getRequired(String name) throws ReferenceException

    • name: String - dependency name to locate.
    • returns: List - list with found dependencies.

      put

      Adds a new dependency into this resolver.

      public void put(String name, Object locator)

      • name: String - dependency’s name.
      • locator: Object - locator to find the dependency by.

      setReferences

      Sets the component references. References must match configured dependencies.

      public void setReferences(IReferences references)

      Static methods

      fromTuples

      Creates a new DependencyResolver from a list of key-value pairs called tuples where key is a dependency name and value the depedency locator (descriptor).

      public static DependencyResolver fromTuples(Object… tuples)

      • tuples: Object… - list of values where odd elements are dependency names and the following even elements are dependency locators (descriptor).
      • returns: DependencyResolver - newly created DependencyResolver.

      Examples

      {
  class MyComponent implements IConfigurable, IReferenceable {
    private DependencyResolver _dependencyResolver = new DependencyResolver();
    private IMyPersistence _persistence;
    ...
 
    public MyComponent() {
      this._dependencyResolver.put("persistence", new Descriptor("mygroup", "persistence", "*", "*", "1.0"));
      }
 
    public void configure(ConfigParams config) {
      this._dependencyResolver.configure(config);
    }
 
    public void setReferences(IReferences references) {
      this._dependencyResolver.setReferences(references);
      this._persistence = (IMyPersistence)this._dependencyResolver.getOneRequired("persistence");
    }
  }
 
  // Create mycomponent and set specific dependency out of many
  MyComponent component = new MyComponent();
  component.configure(ConfigParams.fromTuples(
    "dependencies.persistence", "mygroup:persistence:*:persistence2:1.0" // Override default persistence dependency
  ));
  component.setReferences(References.fromTuples(
    new Descriptor("mygroup","persistence","*","persistence1","1.0"), new MyPersistence(),
    new Descriptor("mygroup","persistence","*","persistence2","1.0"), new MyPersistence()  // This dependency shall be set
  ));
  }

      See also