org.apache.flink.statefun.sdk.state.PersistedValue 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.flink.statefun.sdk.state;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Supplier;
import org.apache.flink.statefun.sdk.StatefulFunction;
import org.apache.flink.statefun.sdk.annotations.ForRuntime;
import org.apache.flink.statefun.sdk.annotations.Persisted;
/**
* A {@link PersistedValue} is a value registered within {@link StatefulFunction}s and is persisted
* and maintained by the system for fault-tolerance.
*
* Created persisted values must be registered by using the {@link Persisted} annotation. Please
* see the class-level Javadoc of {@link StatefulFunction} for an example on how to do that.
*
* @see StatefulFunction
* @param type of the state.
*/
public final class PersistedValue {
private final String name;
private final Class type;
private final Expiration expiration;
private Accessor accessor;
private PersistedValue(String name, Class type, Expiration expiration, Accessor accessor) {
this.name = Objects.requireNonNull(name);
this.type = Objects.requireNonNull(type);
this.expiration = Objects.requireNonNull(expiration);
this.accessor = Objects.requireNonNull(accessor);
}
/**
* Creates a {@link PersistedValue} instance that may be used to access persisted state managed by
* the system. Access to the persisted value is identified by an unique name and type of the
* value. These may not change across multiple executions of the application.
*
* @param name the unique name of the persisted state.
* @param type the type of the state values of this {@code PersistedValue}.
* @param the type of the state values.
* @return a {@code PersistedValue} instance.
*/
public static PersistedValue of(String name, Class type) {
return of(name, type, Expiration.none());
}
/**
* Creates a {@link PersistedValue} instance that may be used to access persisted state managed by
* the system. Access to the persisted value is identified by an unique name and type of the
* value. These may not change across multiple executions of the application.
*
* @param name the unique name of the persisted state.
* @param type the type of the state values of this {@code PersistedValue}.
* @param expiration state expiration configuration.
* @param the type of the state values.
* @return a {@code PersistedValue} instance.
*/
public static PersistedValue of(String name, Class type, Expiration expiration) {
return new PersistedValue<>(name, type, expiration, new NonFaultTolerantAccessor<>());
}
/**
* Returns the unique name of the persisted value.
*
* @return unique name of the persisted value.
*/
public String name() {
return name;
}
/**
* Returns the type of the persisted values.
*
* @return the type of the persisted values.
*/
public Class type() {
return type;
}
public Expiration expiration() {
return expiration;
}
/**
* Returns the persisted value.
*
* @return the persisted value.
*/
public T get() {
return accessor.get();
}
/**
* Updates the persisted value.
*
* @param value the new value.
*/
public void set(T value) {
accessor.set(value);
}
/** Clears the persisted value. After being cleared, the value would be {@code null}. */
public void clear() {
accessor.clear();
}
/**
* Updates the persisted value and returns it, in a single operation.
*
* @param update function to process the previous value to obtain the new value.
* @return the new updated value.
*/
public T updateAndGet(Function update) {
T current = accessor.get();
T updated = update.apply(current);
accessor.set(updated);
return updated;
}
/**
* Attempts to get the persisted value. If the current value is {@code null}, then a specified
* default is returned instead.
*
* @param orElse the default value to return if the current value is not present.
* @return the persisted value, or the provided default if it isn't present.
*/
public T getOrDefault(T orElse) {
T value = accessor.get();
return value != null ? value : orElse;
}
/**
* Attempts to get the persisted value. If the current value is {@code null}, then a default value
* obtained from a specified supplier is returned instead.
*
* @param defaultSupplier supplier for a default value to be used if the current value is not
* present.
* @return the persisted value, or a default value if it isn't present.
*/
public T getOrDefault(Supplier defaultSupplier) {
T value = accessor.get();
return value != null ? value : defaultSupplier.get();
}
@ForRuntime
void setAccessor(Accessor newAccessor) {
Objects.requireNonNull(newAccessor);
this.accessor = newAccessor;
}
@Override
public String toString() {
return String.format(
"PersistedValue{name=%s, type=%s, expiration=%s}", name, type.getName(), expiration);
}
private static final class NonFaultTolerantAccessor implements Accessor {
private E element;
@Override
public void set(E element) {
this.element = element;
}
@Override
public E get() {
return element;
}
@Override
public void clear() {
element = null;
}
}
}