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Hutool是一个小而全的Java工具类库，通过静态方法封装，降低相关API的学习成本，提高工作效率，使Java拥有函数式语言般的优雅，让Java语言也可以“甜甜的”。
There is a newer version: 5.8.34
package cn.hutool.cache.impl;

import cn.hutool.cache.Cache;
import cn.hutool.cache.CacheListener;
import cn.hutool.core.exceptions.ExceptionUtil;
import cn.hutool.core.lang.func.Func0;
import cn.hutool.core.lang.mutable.Mutable;
import cn.hutool.core.lang.mutable.MutableObj;
import cn.hutool.core.map.SafeConcurrentHashMap;

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.atomic.LongAdder;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.stream.Collectors;

/**
 * 超时和限制大小的缓存的默认实现

 * 继承此抽象缓存需要：

 * 
 * 创建一个新的Map
 * 实现 {@code prune} 策略
 * 
 *
 * @param  键类型
 * @param  值类型
 * @author Looly, jodd
 */
public abstract class AbstractCache implements Cache {
	private static final long serialVersionUID = 1L;

	protected Map, CacheObj> cacheMap;

	/**
	 * 写的时候每个key一把锁，降低锁的粒度
	 */
	protected final SafeConcurrentHashMap keyLockMap = new SafeConcurrentHashMap<>();

	/**
	 * 返回缓存容量，{@code 0}表示无大小限制
	 */
	protected int capacity;
	/**
	 * 缓存失效时长， {@code 0} 表示无限制，单位毫秒
	 */
	protected long timeout;

	/**
	 * 每个对象是否有单独的失效时长，用于决定清理过期对象是否有必要。
	 */
	protected boolean existCustomTimeout;

	/**
	 * 命中数，即命中缓存计数
	 */
	protected LongAdder hitCount = new LongAdder();
	/**
	 * 丢失数，即未命中缓存计数
	 */
	protected LongAdder missCount = new LongAdder();

	/**
	 * 缓存监听
	 */
	protected CacheListener listener;

	// ---------------------------------------------------------------- put start
	@Override
	public void put(K key, V object) {
		put(key, object, timeout);
	}

	/**
	 * 加入元素，无锁
	 *
	 * @param key     键
	 * @param object  值
	 * @param timeout 超时时长
	 * @since 4.5.16
	 */
	protected void putWithoutLock(K key, V object, long timeout) {
		CacheObj co = new CacheObj<>(key, object, timeout);
		if (timeout != 0) {
			existCustomTimeout = true;
		}
		if (isFull()) {
			pruneCache();
		}
		cacheMap.put(MutableObj.of(key), co);
	}
	// ---------------------------------------------------------------- put end

	// ---------------------------------------------------------------- get start
	/**
	 * @return 命中数
	 */
	public long getHitCount() {
		return hitCount.sum();
	}

	/**
	 * @return 丢失数
	 */
	public long getMissCount() {
		return missCount.sum();
	}

	@Override
	public V get(K key, boolean isUpdateLastAccess, Func0 supplier) {
		return get(key, isUpdateLastAccess, this.timeout, supplier);
	}

	@Override
	public V get(K key, boolean isUpdateLastAccess, long timeout, Func0 supplier) {
		V v = get(key, isUpdateLastAccess);
		if (null == v && null != supplier) {
			//每个key单独获取一把锁，降低锁的粒度提高并发能力，see pr#1385@Github
			final Lock keyLock = keyLockMap.computeIfAbsent(key, k -> new ReentrantLock());
			keyLock.lock();
			try {
				// 双重检查锁，防止在竞争锁的过程中已经有其它线程写入
				final CacheObj co = getWithoutLock(key);
				if (null == co || co.isExpired()) {
					try {
						v = supplier.call();
					} catch (Exception e) {
						// issue#I7RJZT 运行时异常不做包装
						throw ExceptionUtil.wrapRuntime(e);
						//throw new RuntimeException(e);
					}
					put(key, v, timeout);
				} else {
					v = co.get(isUpdateLastAccess);
				}
			} finally {
				keyLock.unlock();
				keyLockMap.remove(key);
			}
		}
		return v;
	}

	/**
	 * 获取键对应的{@link CacheObj}
	 * @param key 键，实际使用时会被包装为{@link MutableObj}
	 * @return {@link CacheObj}
	 * @since 5.8.0
	 */
	protected CacheObj getWithoutLock(K key){
		return this.cacheMap.get(MutableObj.of(key));
	}
	// ---------------------------------------------------------------- get end

	@Override
	public Iterator iterator() {
		CacheObjIterator copiedIterator = (CacheObjIterator) this.cacheObjIterator();
		return new CacheValuesIterator<>(copiedIterator);
	}
	// ---------------------------------------------------------------- prune start
	/**
	 * 清理实现

	 * 子类实现此方法时无需加锁
	 *
	 * @return 清理数
	 */
	protected abstract int pruneCache();
	// ---------------------------------------------------------------- prune end

	// ---------------------------------------------------------------- common start
	@Override
	public int capacity() {
		return capacity;
	}

	/**
	 * @return 默认缓存失效时长。

	 * 每个对象可以单独设置失效时长
	 */
	@Override
	public long timeout() {
		return timeout;
	}

	/**
	 * 只有设置公共缓存失效时长或每个对象单独的失效时长时清理可用
	 *
	 * @return 过期对象清理是否可用，内部使用
	 */
	protected boolean isPruneExpiredActive() {
		return (timeout != 0) || existCustomTimeout;
	}

	@Override
	public boolean isFull() {
		return (capacity > 0) && (cacheMap.size() >= capacity);
	}

	@Override
	public int size() {
		return cacheMap.size();
	}

	@Override
	public boolean isEmpty() {
		return cacheMap.isEmpty();
	}

	@Override
	public String toString() {
		return this.cacheMap.toString();
	}
	// ---------------------------------------------------------------- common end

	/**
	 * 设置监听
	 *
	 * @param listener 监听
	 * @return this
	 * @since 5.5.2
	 */
	@Override
	public AbstractCache setListener(CacheListener listener) {
		this.listener = listener;
		return this;
	}

	/**
	 * 返回所有键
	 *
	 * @return 所有键
	 * @since 5.5.9
	 */
	public Set keySet(){
		return this.cacheMap.keySet().stream().map(Mutable::get).collect(Collectors.toSet());
	}

	/**
	 * 对象移除回调。默认无动作

	 * 子类可重写此方法用于监听移除事件，如果重写，listener将无效
	 *
	 * @param key          键
	 * @param cachedObject 被缓存的对象
	 */
	protected void onRemove(K key, V cachedObject) {
		final CacheListener listener = this.listener;
		if (null != listener) {
			listener.onRemove(key, cachedObject);
		}
	}

	/**
	 * 移除key对应的对象，不加锁
	 *
	 * @param key           键
	 * @return 移除的对象，无返回null
	 */
	protected CacheObj removeWithoutLock(K key) {
		return cacheMap.remove(MutableObj.of(key));
	}

	/**
	 * 获取所有{@link CacheObj}值的{@link Iterator}形式
	 * @return {@link Iterator}
	 * @since 5.8.0
	 */
	protected Iterator> cacheObjIter(){
		return this.cacheMap.values().iterator();
	}
}