org.apache.jackrabbit.oak.spi.commit.Observer Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jackrabbit.oak.spi.commit;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import org.apache.jackrabbit.oak.spi.state.NodeState;
/**
* Extension point for observing changes in an Oak repository. Observer
* implementations might use the observed content changes to update caches,
* trigger JCR-level observation events or otherwise process the changes.
*
* An observer is informed about content changes by calling the
* {@link #contentChanged(NodeState, CommitInfo)} method. The frequency and
* granularity of these callbacks is not specified. However, each observer is
* always guaranteed to see a linear sequence of changes. In other words the
* method will not be called concurrently from multiple threads and successive
* calls represent a linear sequence of repository states, i.e. the root
* state passed to a call is guaranteed to represent a repository state
* that is not newer than the root state passed to the next call. The observer
* is expected to keep track of the previously observed state if it wants to
* use a content diff to determine what exactly changed between two states.
*
* A repository may capture the optional {@link CommitInfo} instance passed
* to a commit and make it available to observers along with the committed
* content changes. In such cases, i.e. when the commit info argument is
* non-{@code null}, the reported content change is guaranteed to contain
* only changes from that specific commit (and the applied commit
* hooks). Note that it is possible for a repository to report commit
* information for only some commits but not others.
*
* It should also be noted that two observers may not necessarily see the
* same sequence of content changes. It is also possible for an observer to
* be notified when no actual content changes have happened therefore passing
* the same root state to subsequent calls.
*
* A specific implementation or deployment may offer more guarantees about
* when and how observers are notified of content changes. See the relevant
* documentation for more details about such cases.
*
* @since Oak 0.11
*/
public interface Observer {
/**
* Observes a content change. See the {@link Observer} class javadocs
* and relevant repository and observer registration details for more
* information on when and how this method gets called.
*
* @param root root state of the repository
* @param info local commit information, or {@code null}
*/
void contentChanged(@Nonnull NodeState root, @Nullable CommitInfo info);
}