java - WeakHashMap和WeakReference

如何自动清除instanceMap的键和值；当使用WeakHashMap和WeakReference回收getInstance（）API返回的Conf对象时...？

//single conference instance per ConferenceID
class Conf {

    private static HashMap<String, Conf> instanceMap = new HashMap<String, Conf>;

    /*
     * Below code will avoid two threads are requesting
     * to create conference with same confID.
     */
    public static Conf getInstance(String confID){
        //This below synch will ensure singleTon created per confID
        synchronized(Conf.Class) {
           Conf conf = instanceMap.get(confID);
           if(conf == null) {
                 conf = new Conf();
                 instanceMap.put(confID, conf);
           }
           return conf;
        }
    }
}

最佳答案

如果要在丢弃密钥时进行清理，请使用WeakHashMap。如果要清除某个值，则需要自己进行。

private static final Map<String, WeakReference<Conf>> instanceMap = new HashMap<>;

/*
 * Below code will avoid two threads are requesting
 * to create conference with same confID.
 */
public static synchronized Conf getInstance(String confID){
    //This below synch will ensure singleTon created per confID

    WeakReference<Conf> ref = instanceMap.get(confID);
    Conf conf;
    if(ref == null || (conf = ref.get()) == null) {
        conf = new Conf();
        instanceMap.put(confID, new WeakReference<Conf>(conf));
    }
    return conf;
}

注意：这可能会留下死键。如果您不希望这样做，则需要清理它们。

for(Iterator<WeakReference<Conf>> iter = instanceMap.values().iterator(); iter.hashNext() ; ) {
    WeakReference<Conf> ref = iter.next();
    if (ref.get() == null) iter.remove();
}

关于java - WeakHashMap和WeakReference，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/19134401/