Package com.launchdarkly.sdk.server.interfaces

Interface FlagTracker

public interface FlagTracker

An interface for tracking changes in feature flag configurations.

An implementation of this interface is returned by LDClientInterface.getFlagTracker(). Application code never needs to implement this interface.

Since:

5.0.0

Method Summary

Modifier and Type	Method	Description
void	addFlagChangeListener(FlagChangeListener listener)	Registers a listener to be notified of feature flag changes in general.
FlagChangeListener	addFlagValueChangeListener(java.lang.String flagKey, LDContext context, FlagValueChangeListener listener)	Registers a listener to be notified of a change in a specific feature flag's value for a specific evaluation context.
void	removeFlagChangeListener(FlagChangeListener listener)	Unregisters a listener so that it will no longer be notified of feature flag changes.

Method Detail

addFlagChangeListener

void addFlagChangeListener(FlagChangeListener listener)

Registers a listener to be notified of feature flag changes in general.

The listener will be notified whenever the SDK receives any change to any feature flag's configuration, or to a user segment that is referenced by a feature flag. If the updated flag is used as a prerequisite for other flags, the SDK assumes that those flags may now behave differently and sends flag change events for them as well.

Note that this does not necessarily mean the flag's value has changed for any particular evaluation context, only that some part of the flag configuration was changed so that it may return a different value than it previously returned for some context. If you want to track flag value changes, use addFlagValueChangeListener(String, LDContext, FlagValueChangeListener) instead.

If using the file data source (FileData), any change in a data file will be treated as a change to every flag. Again, use addFlagValueChangeListener(String, LDContext, FlagValueChangeListener) (or just re-evaluate the flag yourself) if you want to know whether this is a change that really affects a flag's value.

Change events only work if the SDK is actually connecting to LaunchDarkly (or using the file data source). If the SDK is only reading flags from a database (Components.externalUpdatesOnly()) then it cannot know when there is a change, because flags are read on an as-needed basis.

The listener will be called from a worker thread.

Calling this method for an already-registered listener has no effect.

Parameters:

listener - the event listener to register

See Also:

removeFlagChangeListener(FlagChangeListener), FlagChangeListener, addFlagValueChangeListener(String, LDContext, FlagValueChangeListener)

removeFlagChangeListener

void removeFlagChangeListener(FlagChangeListener listener)

Unregisters a listener so that it will no longer be notified of feature flag changes.

Calling this method for a listener that was not previously registered has no effect.

Parameters:

listener - the event listener to unregister

See Also:

addFlagChangeListener(FlagChangeListener), addFlagValueChangeListener(String, LDContext, FlagValueChangeListener), FlagChangeListener

addFlagValueChangeListener

FlagChangeListener addFlagValueChangeListener(java.lang.String flagKey,
                                              LDContext context,
                                              FlagValueChangeListener listener)

Registers a listener to be notified of a change in a specific feature flag's value for a specific evaluation context.

When you call this method, it first immediately evaluates the feature flag. It then uses addFlagChangeListener(FlagChangeListener) to start listening for feature flag configuration changes, and whenever the specified feature flag changes, it re-evaluates the flag for the same context. It then calls your FlagValueChangeListener if and only if the resulting value has changed.

All feature flag evaluations require an instance of LDContext. If the feature flag you are tracking does not have any user targeting rules, you must still pass a dummy context such as LDContext.create("for-global-flags"). If you do not want the user to appear on your dashboard, use the anonymous property: LDContext.builder("for-global-flags").anonymous(true).build().

The returned FlagChangeListener represents the subscription that was created by this method call; to unsubscribe, pass that object (not your FlagValueChangeListener) to removeFlagChangeListener(FlagChangeListener).

Parameters:

flagKey - the flag key to be evaluated

context - the evaluation context

listener - an object that you provide which will be notified of changes

Returns:

a FlagChangeListener that can be used to unregister the listener

Since:

6.0.0