#949 Create ExpiringSet, integrate into SessionManager

src/main/java/fr/xephi/authme/util/ExpiringSet.java

@@ -0,0 +1,97 @@
+package fr.xephi.authme.util;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Set whose entries expire after a configurable amount of time. Once an entry
+ * has expired, the set will act as if the entry no longer exists. Time starts
+ * counting after the entry has been inserted.
+ * <p>
+ * Internally, expired entries are not cleared automatically. A cleanup can be
+ * triggered with {@link #removeExpiredEntries()}. Adding an entry that is
+ * already present effectively resets its expiration.
+ *
+ * @param <E> the type of the entries
+ */
+public class ExpiringSet<E> {
+
+    private Map<E, Long> entries = new ConcurrentHashMap<>();
+    private long expirationMillis;
+
+    /**
+     * Constructor.
+     *
+     * @param duration the duration of time after which entries expire
+     * @param unit the time unit in which {@code duration} is expressed
+     */
+    public ExpiringSet(long duration, TimeUnit unit) {
+        setExpiration(duration, unit);
+    }
+
+    /**
+     * Adds an entry to the set.
+     *
+     * @param entry the entry to add
+     */
+    public void add(E entry) {
+        entries.put(entry, System.currentTimeMillis() + expirationMillis);
+    }
+
+    /**
+     * Returns whether this set contains the given entry, if it hasn't expired.
+     *
+     * @param entry the entry to check
+     * @return true if the entry is present and not expired, false otherwise
+     */
+    public boolean contains(E entry) {
+        Long expiration = entries.get(entry);
+        return expiration != null && expiration > System.currentTimeMillis();
+    }
+
+    /**
+     * Removes the given entry from the set (if present).
+     *
+     * @param entry the entry to remove
+     */
+    public void remove(E entry) {
+        entries.remove(entry);
+    }
+
+    /**
+     * Removes all entries from the set.
+     */
+    public void clear() {
+        entries.clear();
+    }
+
+    /**
+     * Removes all entries which have expired from the internal structure.
+     */
+    public void removeExpiredEntries() {
+        entries.entrySet().removeIf(entry -> System.currentTimeMillis() > entry.getValue());
+    }
+
+    /**
+     * Sets a new expiration duration. Note that already present entries
+     * will still make use of the old expiration.
+     *
+     * @param duration the duration of time after which entries expire
+     * @param unit the time unit in which {@code duration} is expressed
+     */
+    public void setExpiration(long duration, TimeUnit unit) {
+        this.expirationMillis = unit.toMillis(duration);
+    }
+
+    /**
+     * Returns whether this map is empty. This reflects the state of the
+     * internal map, which may contain expired entries only. The result
+     * may change after running {@link #removeExpiredEntries()}.
+     *
+     * @return true if map is really empty, false otherwise
+     */
+    public boolean isEmpty() {
+        return entries.isEmpty();
+    }
+}