Add method for getting TTL for redis entity

wizard-server/src/main/java/org/cobbzilla/wizard/cache/redis/RedisService.java

@@ -118,6 +118,11 @@ public class RedisService {
     public String get_withPrefix(String prefixedKey) { return decrypt(__get(prefixedKey, 0)); }
     public String get_plaintext(String key) { return __get(prefix(key), 0); }
 
+    /**
+     * @param key
+     * @return TTL in seconds for the given key
+     */
+    public int get_ttl(final String key) { return __ttl(prefix(key), 0).intValue(); }
 
     public <T> void setObject(String key, T thing) { __set(prefix(key), encrypt(toJsonOrDie(thing)), 0); }
     public void set(String key, String value) { __set(prefix(key), encrypt(value), 0); }
@@ -332,6 +337,18 @@ public class RedisService {
         }
     }
 
+    private Long __ttl(final String fullKey, final int attempt) {
+        try {
+            synchronized (redis) {
+                return getRedis().ttl(fullKey);
+            }
+        } catch (RuntimeException e) {
+            if (attempt > MAX_RETRIES) throw e;
+            resetForRetry(attempt, "retrying RedisService.__ttl");
+            return __ttl(fullKey, attempt + 1);
+        }
+    }
+
     private boolean __exists(final String fullKey, final int attempt) {
         try {
             synchronized (redis) {