org.apache.nifi.components.state

Interface StateProvider

All Superinterfaces:

ConfigurableComponent

public interface StateProvider
extends ConfigurableComponent

Provides a mechanism by which components can store and retrieve state. Depending on the Provider, the state may be stored locally, or it may be stored on a remote resource.

Which implementation should be used for local and clustered state is configured in the NiFi properties file. It is therefore possible to provide custom implementations of this interface. Note, however, that this interface is new as of version 0.5.0 of Apache NiFi and may not be considered "stable" as of yet. Therefore, it is subject to change without notice, so providing custom implementations is cautioned against until the API becomes more stable.

Since:

0.5.0

Method Summary

Methods

Modifier and Type	Method and Description
void	clear(String componentId) Removes all values from the component's state that is stored using the given scope
void	disable() Notifies the state provider that it should stop servicing requests to store and retrieve state and instead throw a ProviderDisabledException if any request is made to do so
void	enable() Notifies the state provider that it should begin servicing requests to store and retrieve state
StateMap	getState(String componentId) Returns the currently configured state for the component.
Scope[]	getSupportedScopes() Provides a listing of Scopes supported by the StateProvider
void	initialize(StateProviderInitializationContext context) Initializes the StateProvider so that it is capable of being used.
boolean	isEnabled()
void	onComponentRemoved(String componentId) This method is called whenever a component is removed from the NiFi instance.
boolean	replace(StateMap oldValue, Map<String,String> newValue, String componentId) Updates the value of the component's state to the new value if and only if the value currently is the same as the given oldValue.
void	setState(Map<String,String> state, String componentId) Updates the value of the component's state, setting the new value to the given state
void	shutdown() Shuts down the StateProvider and cleans up any resources held by it.

Methods inherited from interface org.apache.nifi.components.ConfigurableComponent

getIdentifier, getPropertyDescriptor, getPropertyDescriptors, onPropertyModified, validate

Method Detail

initialize

void initialize(StateProviderInitializationContext context)
                throws IOException

Initializes the StateProvider so that it is capable of being used. This method will be called once before any of the other methods are called and will not be called again until the shutdown() method has been called

Parameters:

context - the initialization context that can be used to prepare the state provider for use

Throws:

IOException

shutdown

void shutdown()

Shuts down the StateProvider and cleans up any resources held by it. Once this method has returned, the StateProvider may be initialized once again via the initialize(StateProviderInitializationContext) method.

setState

void setState(Map<String,String> state,
            String componentId)
              throws IOException

Updates the value of the component's state, setting the new value to the given state

Parameters:

state - the value to change the state to

componentId - the id of the component for which state is being set

Throws:

IOException - if unable to communicate with the underlying storage mechanism

getState

StateMap getState(String componentId)
                  throws IOException

Returns the currently configured state for the component. The returned StateMap will never be null. The version of the StateMap will be -1 and the state will contain no key/value pairs if the state has never been set.

Parameters:

componentId - the id of the component for which state is to be retrieved

Returns:

the currently configured value for the component's state

Throws:

IOException - if unable to communicate with the underlying storage mechanism

replace

boolean replace(StateMap oldValue,
              Map<String,String> newValue,
              String componentId)
                throws IOException

Updates the value of the component's state to the new value if and only if the value currently is the same as the given oldValue.

Parameters:

oldValue - the old value to compare against

newValue - the new value to use if and only if the state's value is the same as the given oldValue

componentId - the id of the component for which state is being retrieved

Returns:

true if the state was updated to the new value, false if the state's value was not equal to oldValue

Throws:

IOException - if unable to communicate with the underlying storage mechanism

clear

void clear(String componentId)
           throws IOException

Removes all values from the component's state that is stored using the given scope

Parameters:

componentId - the id of the component for which state is being cleared

Throws:

IOException - if unable to communicate with the underlying storage mechanism

onComponentRemoved

void onComponentRemoved(String componentId)
                        throws IOException

This method is called whenever a component is removed from the NiFi instance. This allows the State Provider to perform tasks when a component is removed in order to clean up resources that may be associated with that component

Parameters:

componentId - the ID of the component that was added to the NiFi instance

Throws:

IOException - if unable to perform the necessary cleanup

enable

void enable()

Notifies the state provider that it should begin servicing requests to store and retrieve state

disable

void disable()

Notifies the state provider that it should stop servicing requests to store and retrieve state and instead throw a ProviderDisabledException if any request is made to do so

isEnabled

boolean isEnabled()

Returns:

true if the provider is enabled, false otherwise.

getSupportedScopes

Scope[] getSupportedScopes()

Provides a listing of Scopes supported by the StateProvider

Returns:

the Scopes supported by the configuration