In put method, we can specify action to be executed when item is expired

Add shutdown method to TTL map to shutdown the underlying scheduled executor

Author: athingforcode-eng

.idea/workspace.xml

@@ -5,14 +5,19 @@
 public class Main {
     public static void main(String[] args) throws InterruptedException {
         TTLHashMap<String, String> map = new TTLHashMap<>();
-        map.put("key1", "value1", 5, TimeUnit.SECONDS);
-        map.put("key2", "value2", 10, TimeUnit.SECONDS);
+        map.put("key1", "value1", 5, TimeUnit.SECONDS, null);
+        map.put("key2", "value2", 10, TimeUnit.SECONDS, null);
+
+        map.put("key3", "value3", 5, TimeUnit.SECONDS, (key,value) -> System.out.println("Action executed when key-"+ key + " expired, its value is : " + value));
+        map.put("key4", "value4", 10, TimeUnit.SECONDS, (key,value) -> System.out.println("Action executed when key-"+ key + " expired, its value is : " + value));
 
         System.out.println(map.get("key1")); // prints "value1"
-        Thread.sleep(6000);
+        Thread.sleep(12000);
         System.out.println(map.get("key1")); // prints null
-        System.out.println(map.get("key2")); // prints "value2"
+        System.out.println(map.get("key2")); // prints null
         map.remove("key2");
         System.out.println(map.get("key2")); // prints "null"
+
+        map.shutdown();
     }
 }

src/main/java/com/athingforcode/Main.java

@@ -1,9 +1,11 @@
 package com.athingforcode;
 
+import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
+import java.util.function.BiConsumer;
 
 public class TTLHashMap<K, V> {
     private final ConcurrentHashMap<K, Entry<K, V>> map;
@@ -14,10 +16,18 @@ public TTLHashMap() {
         this.scheduler = Executors.newSingleThreadScheduledExecutor();
     }
 
-    public void put(K key, V value, long ttl, TimeUnit unit) {
+    public void shutdown() {
+        scheduler.shutdownNow();
+    }
+
+    public void put(K key, V value, long ttl, TimeUnit unit, BiConsumer<K, V> actionWhenExpired) {
+        Objects.requireNonNull(key);
         Entry<K, V> entry = new Entry<>(key, value, ttl, unit);
         map.put(key, entry);
-        setRemovalSchedule(entry);
+        //if ttl is negative then entry is cosidered non expiring
+        if(ttl >= 0) {
+            setRemovalSchedule(entry,actionWhenExpired);
+        }
     }
 
     public V get(K key) {
@@ -33,9 +43,12 @@ public void remove(K key) {
         map.remove(key);
     }
 
-    private void setRemovalSchedule(Entry<K, V> entry) {
+    private void setRemovalSchedule(Entry<K, V> entry, BiConsumer<K, V> actionWhenExpired) {
         scheduler.schedule(() -> {
             map.remove(entry.getKey());
+            if(actionWhenExpired != null) {
+                actionWhenExpired.accept(entry.getKey(), entry.getValue());
+            }
         }, entry.getTTL(), entry.getTtlUnit());
     }