netty5/common/src/main/java/io/netty/util/ConstantPool.java

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/*
* Copyright 2013 The Netty Project
*
* The Netty Project 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 io.netty.util;
import java.util.HashMap;
import java.util.Map;
/**
* A pool of {@link Constant}s.
*
* @param <T> the type of the constant
*/
public abstract class ConstantPool<T extends Constant<T>> {
private final Map<String, T> constants = new HashMap<String, T>();
private int nextId = 1;
/**
* Shortcut of {@link #valueOf(String) valueOf(firstNameComponent.getName() + "#" + secondNameComponent)}.
*/
public T valueOf(Class<?> firstNameComponent, String secondNameComponent) {
if (firstNameComponent == null) {
throw new NullPointerException("firstNameComponent");
}
if (secondNameComponent == null) {
throw new NullPointerException("secondNameComponent");
}
return valueOf(firstNameComponent.getName() + '#' + secondNameComponent);
}
/**
* Returns the {@link Constant} which is assigned to the specified {@code name}.
* If there's no such {@link Constant}, a new one will be created and returned.
* Once created, the subsequent calls with the same {@code name} will always return the previously created one
* (i.e. singleton.)
*
* @param name the name of the {@link Constant}
*/
public T valueOf(String name) {
if (name == null) {
throw new NullPointerException("name");
}
if (name.isEmpty()) {
throw new IllegalArgumentException("empty name");
}
synchronized (constants) {
T c = constants.get(name);
if (c == null) {
c = newConstant(nextId, name);
constants.put(name, c);
nextId ++;
}
return c;
}
}
protected abstract T newConstant(int id, String name);
}