增长LinkedCacheMap工具类

2026-10-23 07:54:28 +08:00 · 2018-07-29 16:06:56 +08:00
parent 025f8c376f
commit 30ce55bba2
1 changed files with 140 additions and 0 deletions
@@ -0,0 +1,140 @@
+package com.kingston.jforgame.common.utils;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * 基于LinkedHashMap实现的一个有限队列缓存 有时间及大小的限制
+ * aliveTime参数为true时要模拟lru规则
+ * 
+ * @author kingston
+ */
+public class LinkedCacheMap<K, V> {
+
+	private LinkedHashMap<K, Element<V>> data;
+
+	/**
+	 * 缓存最大容量，添加新元素时，若当前长度超过容量，则会删除队首元素
+	 */
+	private int capacity;
+
+	/** 生存时长（毫秒数） */
+	private long aliveTime;
+
+	/**
+	 * 是否使用lru规则，为true时表示当元素被查找命中时被重放到队尾
+	 *  {@link LinkedHashMap#accessOrder}}
+	 */
+	private boolean useLru;
+
+	/** 读写锁 */
+	private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
+	private ReentrantReadWriteLock.ReadLock readLock = lock.readLock();
+	private ReentrantReadWriteLock.WriteLock writeLock = lock.writeLock();
+
+	public LinkedCacheMap(int capacity, long aliveTime) {
+		this(capacity, aliveTime, Boolean.FALSE);
+	}
+
+	public LinkedCacheMap(int capacity, long aliveTime, boolean useLru) {
+		this.capacity = capacity;
+		this.aliveTime = aliveTime;
+		this.useLru = useLru;
+		this.data = new LinkedHashMap<K, Element<V>>(capacity, 1.0f, useLru) {
+			private static final long serialVersionUID = 1L;
+
+			@Override
+			protected boolean removeEldestEntry(Map.Entry<K, Element<V>> eldest) {
+				if (size() > capacity) {
+					return true;
+				}
+				long eleAliveTime = System.currentTimeMillis() - eldest.getValue().bornTime;
+				return (eleAliveTime > aliveTime);
+			}
+		};
+	}
+
+	public V put(K key, V value) {
+		V preValue = null;
+		Element<V> newValue = new Element<V>(value);
+
+		readLock.lock();
+		try {
+			if (data.containsKey(key)) {
+				preValue = data.get(key).value;
+			}
+			data.put(key, newValue);
+			return preValue;
+		} finally {
+			readLock.unlock();
+		}
+	}
+
+	public V get(K key) {
+		// 当使用lru，元素重放回队尾涉及到写操作，所以用写锁
+		Lock lock = this.useLru ? this.writeLock : this.readLock;
+		lock.lock();
+		try {
+			Element<V> target = this.data.get(key);
+			return target != null ? target.value : null;
+		} finally {
+			lock.unlock();
+		}
+	}
+	
+	public void clear() {
+		this.writeLock.lock();
+		try {
+			this.data.clear();
+		} finally {
+			this.writeLock.unlock();
+		}
+	}
+
+	@Override
+	public String toString() {
+		return "LinkedCacheMap [data=" + data + ", capacity=" + capacity + ", aliveTime=" + aliveTime + ", useLru="
+				+ useLru + "]";
+	}
+
+	@SuppressWarnings("hiding")
+	class Element<V> {
+		V value;
+		/** 元素添加时的时间戳 */
+		long bornTime;
+
+		Element(V v) {
+			this.value = v;
+			this.bornTime = System.currentTimeMillis();
+		}
+
+		@Override
+		public String toString() {
+			return "Element [value=" + value + "]";
+		}
+	}
+	
+	
+	public static void main(String[] args) throws Exception {
+		LinkedCacheMap<String, String> cache = new LinkedCacheMap<>(3, 100, true);
+		
+		cache.put("a", "a");
+		cache.put("b", "b");
+		cache.put("c", "c");
+		
+		cache.get("a");
+		cache.put("d", "d");
+		
+		System.err.println(cache);
+		
+		cache.clear();
+		cache.put("e", "e");
+		cache.put("f", "f");
+		Thread.sleep(150);
+		cache.put("g", "g");
+		System.err.println(cache);
+	}
+
+}