EDIT

Check if this method is used elsewhere. If not make it deprecated with reason that it currently gives not the expected results but may be fixed in future and link to the ticket and set to Reviewed with priority 11.

There is no change with using Integer.valueOf(i)

Patrick Plitzner wrote:

There is no change with using Integer.valueOf(i)

Ok, this is good news!
Maybe it helps to take a look at the serialization and deserialization of Objects in HttpInvoker.

BTW: You could also test if the serialization and deserialization with jdk is working, see ObjectStreams.

Tested serialization and deserialization for plain java with the following:

    public static void main(String args[]) {

        HashMap<Integer, Integer> map = new HashMap<>();
        for(int i=0;i<100;i++){
            map.put(Integer.valueOf(i),Integer.valueOf(i));
        }
        try{
            FileOutputStream fos =
                    new FileOutputStream("map.file");
            ObjectOutputStream oos = new ObjectOutputStream(fos);
            oos.writeObject(map);
            oos.close();
            fos.close();
            System.out.println("Serialized HashMap data is saved in map.file");

            map = null;
            FileInputStream fis = new FileInputStream("map.file");
            ObjectInputStream ois = new ObjectInputStream(fis);
            map = (HashMap) ois.readObject();
            ois.close();
            fis.close();
        }catch(Exception e) {
            e.printStackTrace();
            return;
        }
        System.out.println("Deserialized HashMap");
        map.forEach((key, value)->System.out.println("key: "+ key + ",  value: "+value));
    }

This works fine. So it must have something to do with the serialization process of spring.

The problem has nothing to do with the deserialization but with CacheLoader.load(Map map, List alreadyVisitedEntities, boolean update) where the Map is not reconstructed correctly.