org.apache.flink.api.common.state.ValueState Maven / Gradle / Ivy
/*
* 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.flink.api.common.state;
import org.apache.flink.annotation.PublicEvolving;
import java.io.IOException;
/**
* {@link State} interface for partitioned single-value state. The value can be retrieved or
* updated.
*
* The state is accessed and modified by user functions, and checkpointed consistently
* by the system as part of the distributed snapshots.
*
*
The state is only accessible by functions applied on a {@code KeyedStream}. The key is
* automatically supplied by the system, so the function always sees the value mapped to the
* key of the current element. That way, the system can handle stream and state partitioning
* consistently together.
*
* @param Type of the value in the state.
*/
@PublicEvolving
public interface ValueState extends State {
/**
* Returns the current value for the state. When the state is not
* partitioned the returned value is the same for all inputs in a given
* operator instance. If state partitioning is applied, the value returned
* depends on the current operator input, as the operator maintains an
* independent state for each partition.
*
* If you didn't specify a default value when creating the {@link ValueStateDescriptor}
* this will return {@code null} when to value was previously set using {@link #update(Object)}.
*
* @return The state value corresponding to the current input.
*
* @throws IOException Thrown if the system cannot access the state.
*/
T value() throws IOException;
/**
* Updates the operator state accessible by {@link #value()} to the given
* value. The next time {@link #value()} is called (for the same state
* partition) the returned state will represent the updated value. When a
* partitioned state is updated with null, the state for the current key
* will be removed and the default value is returned on the next access.
*
* @param value The new value for the state.
*
* @throws IOException Thrown if the system cannot access the state.
*/
void update(T value) throws IOException;
}