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Dahua ICC Open API SDK for Java

There is a newer version: 1.0.13.10

package com.dahuatech.hutool.core.lang;

import com.dahuatech.hutool.core.lang.func.Func0;

import java.io.Serializable;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

/**
 * 简单缓存，无超时实现，使用{@link WeakHashMap}实现缓存自动清理
 *
 * @author Looly
 * @param  键类型
 * @param  值类型
 */
public class SimpleCache implements Serializable {
  private static final long serialVersionUID = 1L;

  /** 池 */
  private final Map cache = new WeakHashMap<>();

  private final ReentrantReadWriteLock cacheLock = new ReentrantReadWriteLock();
  private final ReadLock readLock = cacheLock.readLock();
  private final WriteLock writeLock = cacheLock.writeLock();

  /**
   * 从缓存池中查找值
   *
   * @param key 键
   * @return 值
   */
  public V get(K key) {
    // 尝试读取缓存
    readLock.lock();
    V value;
    try {
      value = cache.get(key);
    } finally {
      readLock.unlock();
    }
    return value;
  }

  /**
   * 从缓存中获得对象，当对象不在缓存中或已经过期返回Func0回调产生的对象
   *
   * @param key 键
   * @param supplier 如果不存在回调方法，用于生产值对象
   * @return 值对象
   */
  public V get(K key, Func0 supplier) {
    V v = get(key);
    if (null == v && null != supplier) {
      writeLock.lock();
      try {
        // 双重检查锁
        v = cache.get(key);
        if (null == v) {
          try {
            v = supplier.call();
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
          cache.put(key, v);
        }
      } finally {
        writeLock.unlock();
      }
    }
    return v;
  }

  /**
   * 放入缓存
   *
   * @param key 键
   * @param value 值
   * @return 值
   */
  public V put(K key, V value) {
    writeLock.lock();
    try {
      cache.put(key, value);
    } finally {
      writeLock.unlock();
    }
    return value;
  }

  /**
   * 移除缓存
   *
   * @param key 键
   * @return 移除的值
   */
  public V remove(K key) {
    writeLock.lock();
    try {
      return cache.remove(key);
    } finally {
      writeLock.unlock();
    }
  }

  /** 清空缓存池 */
  public void clear() {
    writeLock.lock();
    try {
      this.cache.clear();
    } finally {
      writeLock.unlock();
    }
  }
}