/**
* Returns a cursor that allows to retrieve the records from this log. The starting position is
* defined by the provided key, cursor matching strategy and cursor positioning strategy.
*
* @param key Key to use as a start position for the cursor. If key is {@code null}, cursor will
* point at the first record of the log.
* @param matchingStrategy Cursor key matching strategy.
* @param positionStrategy The cursor positioning strategy.
* @return a cursor on the log records, which is never {@code null}
* @throws ChangelogException If the cursor can't be created.
*/
public RepositionableCursor<K, V> getCursor(
final K key,
final KeyMatchingStrategy matchingStrategy,
final PositionStrategy positionStrategy)
throws ChangelogException {
if (key == null) {
return getCursor();
}
AbortableLogCursor<K, V> cursor = null;
sharedLock.lock();
try {
if (isClosed) {
return new EmptyCursor<>();
}
cursor = new AbortableLogCursor<>(this, new InternalLogCursor<K, V>(this));
final boolean isSuccessfullyPositioned =
cursor.positionTo(key, matchingStrategy, positionStrategy);
// Allow for cursor re-initialization after exhaustion in case of
// LESS_THAN_OR_EQUAL_TO_KEY ands GREATER_THAN_OR_EQUAL_TO_KEY strategies
if (isSuccessfullyPositioned || matchingStrategy != EQUAL_TO_KEY) {
registerCursor(cursor);
return cursor;
} else {
StaticUtils.close(cursor);
return new EmptyCursor<>();
}
} catch (ChangelogException e) {
StaticUtils.close(cursor);
throw e;
} finally {
sharedLock.unlock();
}
}
/**
* Returns a cursor that allows to retrieve the records from this log, starting at the first
* position.
*
* @return a cursor on the log records, which is never {@code null}
* @throws ChangelogException If the cursor can't be created.
*/
public RepositionableCursor<K, V> getCursor() throws ChangelogException {
AbortableLogCursor<K, V> cursor = null;
sharedLock.lock();
try {
if (isClosed) {
return new EmptyCursor<>();
}
cursor = new AbortableLogCursor<>(this, new InternalLogCursor<K, V>(this));
cursor.positionTo(null, null, null);
registerCursor(cursor);
return cursor;
} catch (ChangelogException e) {
StaticUtils.close(cursor);
throw e;
} finally {
sharedLock.unlock();
}
}
