org.apache.sshd.common.AttributeStore 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.sshd.common;
import java.util.Objects;
import java.util.function.Function;
/**
* Provides the capability to attach in-memory attributes to the entity
*
* @author Apache MINA SSHD Project
*/
public interface AttributeStore extends AttributeRepository {
/**
* If the specified key is not already associated with a value (or is mapped to {@code null}), attempts to compute
* its value using the given mapping function and enters it into this map unless {@code null}.
*
* @param The generic attribute type
* @param key The key of the attribute; must not be {@code null}.
* @param resolver The (never {@code null}) mapping function to use if value not already mapped. If returns
* {@code null} then value is not mapped to the provided key.
* @return The resolved value - {@code null} if value not mapped and resolver did not return a
* non-{@code null} value for it
*/
default T computeAttributeIfAbsent(
AttributeKey key, Function, ? extends T> resolver) {
Objects.requireNonNull(resolver, "No resolver provided");
T value = getAttribute(key);
if (value != null) {
return value;
}
value = resolver.apply(key);
if (value == null) {
return null;
}
setAttribute(key, value);
return value;
}
/**
* Sets a user-defined attribute.
*
* @param The generic attribute type
* @param key The key of the attribute; must not be {@code null}.
* @param value The value of the attribute; must not be {@code null}.
* @return The old value of the attribute; {@code null} if it is new.
*/
T setAttribute(AttributeKey key, T value);
/**
* Removes the user-defined attribute
*
* @param The generic attribute type
* @param key The key of the attribute; must not be {@code null}.
* @return The removed value; {@code null} if no previous value
*/
T removeAttribute(AttributeKey key);
/**
* Removes all currently stored user-defined attributes
*/
void clearAttributes();
}