org.osgi.service.wireadmin

Interface Producer

public interface Producer

Data Producer, a service that can generate values to be used by Consumer services.

Service objects registered under the Producer interface are expected to produce values (internally generated or from external sensors). The value can be of different types. When delivering a value to a Wire object, the Producer service should coerce the value to be an instance of one of the types specified by Wire.getFlavors(). The classes are specified in order of preference.

When the data represented by the Producer object changes, this object should send the updated value by calling the update method on each of Wire objects passed in the most recent call to this object's consumersConnected(Wire[]) method. These Wire objects will pass the value on to the associated Consumer service object.

The Producer service may use the information in the Wire object's properties to schedule the delivery of values to the Wire object.

Producer service objects must register with a service.pid and a WireConstants.WIREADMIN_PRODUCER_FLAVORS property. It is recommended that a Producer service object also registers with a service.description property. Producer service objects must register with a WireConstants.WIREADMIN_PRODUCER_FILTERS property if the Producer service will be performing filtering instead of the Wire object.

If an exception is thrown by a Producer object method, a WireAdminEvent of type WireAdminEvent.PRODUCER_EXCEPTION is broadcast by the Wire Admin service.

Security Considerations. Data producing bundles will require ServicePermission[Producer,REGISTER] to register a Producer service. In general, only the Wire Admin service should have ServicePermission[Producer,GET]. Thus only the Wire Admin service may directly call a Producer service. Care must be taken in the sharing of Wire objects with other bundles.

Producer services must be registered with scope names when they can send different types of objects (composite) to the Consumer service. The Producer service should have WirePermission for each of these scope names.

Method Summary

Methods

Modifier and Type	Method and Description
void	consumersConnected(Wire[] wires) Update the list of Wire objects to which this Producer object is connected.
Object	polled(Wire wire) Return the current value of this Producer object.

Method Detail

polled

Object polled(Wire wire)

Return the current value of this Producer object.

This method is called by a Wire object in response to the Consumer service calling the Wire object's poll method. The Producer should coerce the value to be an instance of one of the types specified by Wire.getFlavors(). The types are specified in order of preference. The returned value should be as new or newer than the last value furnished by this object.

Note: This method may be called by a Wire object prior to this object being notified that it is connected to that Wire object (via the consumersConnected(Wire[]) method).

If the Producer service returns an Envelope object that has an impermissible scope name, then the Wire object must ignore (or remove) the transfer.

If the Wire object has a scope set, the return value must be an array of Envelope objects (Envelope[]). The Wire object must have removed any Envelope objects that have a scope name that is not in the Wire object's scope.

Parameters:

wire - The Wire object which is polling this service.

Returns:

The current value of the Producer service or null if the value cannot be coerced into a compatible type. Or an array of Envelope objects.

consumersConnected

void consumersConnected(Wire[] wires)

Update the list of Wire objects to which this Producer object is connected.

This method is called when the Producer service is first registered and subsequently whenever a Wire associated with this Producer becomes connected, is modified or becomes disconnected.

The Wire Admin service must call this method asynchronously. This implies that implementors of a Producer service can be assured that the callback will not take place during registration when they execute the registration in a synchronized method.

Parameters:

wires - An array of the current and complete list of Wire objects to which this Producer service is connected. May be null if the Producer is not currently connected to any Wire objects.