java 并发学习(一)

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很多情况下我们对缓存数据需要有时效性的要求,可以借助 delayQueue 完成这一工作
import java.util.Map;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.DelayQueue;import java.util.concurrent.Delayed;import java.util.concurrent.TimeUnit;public class AutoCleanMap<K, V> {    private final static Integer DEFAULT_TIME=5;    private final static TimeUnit DEFAULT_TIMEUNIT=TimeUnit.SECONDS;    private  long effectiveTime;    private  TimeUnit timeUnit ;    private Map<K, V> map = new ConcurrentHashMap<K, V>();    private DelayQueue<Data<K>> cleanQueue = new DelayQueue<Data<K>>();    public AutoCleanMap(long effectiveTime, TimeUnit timeUnit) {        this.effectiveTime = effectiveTime;        this.timeUnit = timeUnit;        Thread thread = new Thread() {            public void run() {                for (;;)                    try {                        map.remove(cleanQueue.take().getKey());                    } catch (InterruptedException e) {                        e.printStackTrace();                    }            }        };        thread.setDaemon(true);        thread.start();    }    public AutoCleanMap() {        this(DEFAULT_TIME, DEFAULT_TIMEUNIT);    }    public void put(K key, V value) {        Data<K> data = new Data<K>(key, timeUnit.toNanos(effectiveTime));        synchronized (map) {            if (map.get(key) != null) {                cleanQueue.remove(data);            }            map.put(key, value);        }        cleanQueue.add(data);    }    public V get(K k) {        return map.get(k);    }    private static class Data<K> implements Delayed {        private K key;        private long endTime;        public Data(K key, long effectiveTime) {            super();            this.key = key;            this.endTime = effectiveTime + System.nanoTime();        }        public K getKey() {            return key;        }        @Override        public int compareTo(Delayed o) {            if (!(o instanceof Data))                return 1;            if (this == o)                return 0;            @SuppressWarnings("unchecked")            Data<K> data = (Data<K>) o;            if (this.endTime == data.endTime)                return 0;            return this.endTime > data.endTime ? 1 : -1;        }        @Override        public long getDelay(TimeUnit unit) {            return endTime - System.nanoTime();        }        @Override        public int hashCode() {            final int prime = 31;            int result = 1;            result = prime * result + ((key == null) ? 0 : key.hashCode());            return result;        }        @Override        public boolean equals(Object obj) {            if (this == obj)                return true;            if (obj == null)                return false;            if (getClass() != obj.getClass())                return false;            @SuppressWarnings("unchecked")            Data<K> other = (Data<K>) obj;            if (key == null) {                if (other.key != null)                    return false;            } else if (!key.equals(other.key))                return false;            return true;        }    }}
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