java/io/ExpiringCache.java

0N/A/*
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0N/A
0N/A/*
0N/A */
0N/A
0N/Apackage java.io;
0N/A
0N/Aimport java.util.Iterator;
0N/Aimport java.util.Map;
0N/Aimport java.util.LinkedHashMap;
0N/Aimport java.util.Set;
0N/A
0N/Aclass ExpiringCache {
0N/A    private long millisUntilExpiration;
0N/A    private Map  map;
0N/A    // Clear out old entries every few queries
0N/A    private int queryCount;
0N/A    private int queryOverflow = 300;
0N/A    private int MAX_ENTRIES = 200;
0N/A
0N/A    static class Entry {
0N/A        private long   timestamp;
0N/A        private String val;
0N/A
0N/A        Entry(long timestamp, String val) {
0N/A            this.timestamp = timestamp;
0N/A            this.val = val;
0N/A        }
0N/A
0N/A        long   timestamp()                  { return timestamp;           }
0N/A        void   setTimestamp(long timestamp) { this.timestamp = timestamp; }
0N/A
0N/A        String val()                        { return val;                 }
0N/A        void   setVal(String val)           { this.val = val;             }
0N/A    }
0N/A
0N/A    ExpiringCache() {
0N/A        this(30000);
0N/A    }
0N/A
0N/A    ExpiringCache(long millisUntilExpiration) {
0N/A        this.millisUntilExpiration = millisUntilExpiration;
0N/A        map = new LinkedHashMap() {
0N/A            protected boolean removeEldestEntry(Map.Entry eldest) {
0N/A              return size() > MAX_ENTRIES;
0N/A            }
0N/A          };
    }

    synchronized String get(String key) {
        if (++queryCount >= queryOverflow) {
            cleanup();
        }
        Entry entry = entryFor(key);
        if (entry != null) {
            return entry.val();
        }
        return null;
    }

    synchronized void put(String key, String val) {
        if (++queryCount >= queryOverflow) {
            cleanup();
        }
        Entry entry = entryFor(key);
        if (entry != null) {
            entry.setTimestamp(System.currentTimeMillis());
            entry.setVal(val);
        } else {
            map.put(key, new Entry(System.currentTimeMillis(), val));
        }
    }

    synchronized void clear() {
        map.clear();
    }

    private Entry entryFor(String key) {
        Entry entry = (Entry) map.get(key);
        if (entry != null) {
            long delta = System.currentTimeMillis() - entry.timestamp();
            if (delta < 0 || delta >= millisUntilExpiration) {
                map.remove(key);
                entry = null;
            }
        }
        return entry;
    }

    private void cleanup() {
        Set keySet = map.keySet();
        // Avoid ConcurrentModificationExceptions
        String[] keys = new String[keySet.size()];
        int i = 0;
        for (Iterator iter = keySet.iterator(); iter.hasNext(); ) {
            String key = (String) iter.next();
            keys[i++] = key;
        }
        for (int j = 0; j < keys.length; j++) {
            entryFor(keys[j]);
        }
        queryCount = 0;
    }
}