storm-client/src/jvm/org/apache/storm/state/StateProvider.java

/**
 * 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.storm.state;

import java.util.Map;
import org.apache.storm.task.TopologyContext;

/**
 * Used by the {@link StateFactory} to create a new state instances.
 */
public interface StateProvider {
    /**
     * Returns a new state instance. Each state belongs unique namespace which is typically the componentid-task of the task, so that each
     * task can have its own unique state.
     *
     * @param namespace a namespace of the state
     * @param topoConf  the storm topology configuration
     * @param context   the {@link TopologyContext}
     * @return a previously saved state if one exists otherwise a newly initialized state.
     */
    State newState(String namespace, Map<String, Object> topoConf, TopologyContext context);
}