Merge pull request #6758 from eclipse/jetty-10.0.x-extensible-default…

…-session-cache

Issue #6752 - Extensible DefaultSessionCache map implementation

jetty-server/src/main/java/org/eclipse/jetty/server/session/DefaultSessionCache.java

@@ -13,6 +13,7 @@
 
 package org.eclipse.jetty.server.session;
 
+import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.function.Function;
@@ -28,7 +29,7 @@
 /**
  * DefaultSessionCache
  *
- * A session store that keeps its sessions in memory in a concurrent map
+ * A session store that keeps its sessions in memory within a concurrent map
  */
 @ManagedObject
 public class DefaultSessionCache extends AbstractSessionCache
@@ -38,16 +39,26 @@ public class DefaultSessionCache extends AbstractSessionCache
     /**
      * The cache of sessions in a concurrent map
      */
-    protected ConcurrentMap<String, Session> _sessions = new ConcurrentHashMap<>();
+    private final ConcurrentMap<String, Session> _sessions;
 
     private final CounterStatistic _stats = new CounterStatistic();
 
     /**
      * @param manager The SessionHandler related to this SessionCache
      */
     public DefaultSessionCache(SessionHandler manager)
+    {
+        this(manager, new ConcurrentHashMap<>());
+    }
+
+    /**
+     * @param manager The SessionHandler related to this SessionCache
+     * @param sessions The session map implementation to use
+     */
+    public DefaultSessionCache(SessionHandler manager, ConcurrentMap<String, Session> sessions)
     {
         super(manager);
+        _sessions = Objects.requireNonNull(sessions, "Session Map may not be null");
     }
 
     /**