基于ConcurrentHashMap和WeakHashMap的简单缓存实现 package test; import java.util.Map;import java.util.WeakHashMap;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock; public final class SimpleCache
      
        {     private final Lock lock = new ReentrantLock();    private final int maxCapacity;    private final Map
       
         eden;    private final Map
        
          longterm;     public SimpleCache(int maxCapacity) {        this.maxCapacity = maxCapacity;        this.eden = new ConcurrentHashMap
         
          (maxCapacity);        this.longterm = new WeakHashMap
          
           (maxCapacity);    }     public V get(K k) {        V v = this.eden.get(k);        if (v == null) {            lock.lock();            try{                v = this.longterm.get(k);            }finally{                lock.unlock();            }            if (v != null) {                this.eden.put(k, v);            }        }        return v;    }     public void put(K k, V v) {        if (this.eden.size() >= maxCapacity) {            lock.lock();            try{                this.longterm.putAll(this.eden);            }finally{                lock.unlock();            }            this.eden.clear();        }        this.eden.put(k, v);    }}