ClusterApplier.java example

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 * the Apache License, Version 2.0 (the "License"); you may
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 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
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package org.elasticsearch.cluster.service;

import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.ClusterStateTaskListener;

import java.util.function.Supplier;

public interface ClusterApplier {
    /**
     * Sets the initial state for this applier. Should only be called once.
     * @param initialState the initial state to set
     */
    void setInitialState(ClusterState initialState);

    /**
     * Method to invoke when a new cluster state is available to be applied
     *
     * @param source information where the cluster state came from
     * @param clusterStateSupplier the cluster state supplier which provides the latest cluster state to apply
     * @param listener callback that is invoked after cluster state is applied
     */
    void onNewClusterState(String source, Supplier<ClusterState> clusterStateSupplier, ClusterStateTaskListener listener);
}