public interface Component extends Closeable
This interface defines the basic API and lifecycle of a generic KnowledgeStore internal component, and is specialized for specific types of components.
The lifecycle of a Component is the following:
Component instance is created starting with a number of key/value properties
and using one of the mechanisms supported by Factory (i.e., constructor, static factory
method, builder pattern). The Component instance configures itself based on the
supplied properties. In case the configuration is incorrect, an exception will be thrown;
otherwise, the component is now configured, but still inactive, meaning that no activity is
being carried out by the component, no persistent data is being modified and no resource that
needs to be later freed is being allocated.init() is called to initialize the Component instance and make it
operational; differently from the constructor, method init() is allowed to allocate any
resource, to modify persisted data and to start any task as necessary for the component to
perform its tasks.Component interface are called by external code (e.g., the
frontend). Whether these methods can be called by a thread at a time (meaning the component can
be thread-unsafe) or concurrently by multiple threads (meaning the component must be
thread-safe) depends on the particular type of component, as documented in itsJavadoc.close() is called to dispose the Component object, allowing it to
free allocated resources (e.g., close files and network connections) in an orderly way. Note
that method close() can be called at any time after the component has been instantiated
(even before initialization, in case external failure requires the component to be immediately
disposed). In particular, it is possible for the close() method to be called while a
component method is being invoked by another thread.
Components are expected to access external resources (e.g., storage) or to communicate to
external processes, hence methods in this interface and its specializations may throw
IOExceptions. As a special kind of IOException, they may throw a
DataCorruptedException in case a data corruption situation is detected, possibly
triggering some external recovery procedure.
| Modifier and Type | Method and Description |
|---|---|
void |
close()
Closes this
Component object. |
void |
init()
Initializes the
Component with the supplied Runtime object. |
void init() throws IOException, IllegalStateException
Component with the supplied Runtime object. This method is
called after the instantiation of a Component and before any other instance method
is called. It provides a Runtime that can be used to access runtime services such
as locking, serialization and filesystem access. The Component is allowed to
perform any initialization operation that is necessary in order to become functional; on
failure, these operations may result in a IOException being thrown.IOException - in case initialization failsIllegalStateException - in case the component has already been initialized or closedvoid close()
Component object. If the component has been initialized, closing a it
causes any allocated resource to be freed and any operation or transaction ongoing within
the component being aborted; in case the component has not been initialized yet, or
close() has already being called, calling this method has no effect. Note that the
operation affects only the local Component object and not any remote service this
object may rely on to implement its functionalities; in particular, such a remote service
is not shutdown by the operation, so that it can be accessed by other Component
instances possibly running in other (virtual) machines. Similarly, closing a
Component object has no impact on stored data, that continues to be persisted and
will be accessed unchanged (provided no external modification occurs) the next time a
similarly configured Component is created.close in interface AutoCloseableclose in interface CloseableCopyright © 2015–2016 FBK-irst. All rights reserved.