Android Cache Manager by using gson

package com.yusuf.iris.utils;

import android.content.Context;

import java.util.List;
import java.util.concurrent.ConcurrentHashMap;


import com.yusuf.iris.helpers.Helper;
import com.yusuf.iris.zitem.Session;
import com.google.gson.Gson;

import static com.digiturk.iris.helpers.Helper.PREF_USERSESSION;

public class CacheManagerServiceData {

    private static CacheManagerServiceData mCacheManager;
    public  static ConcurrentHashMap<String, String> mGenericCache;
    public  static ConcurrentHashMap<String, Session> mSessionCache;

    public static synchronized CacheManagerServiceData getInstance() {
        if (mCacheManager == null)
            mCacheManager = new CacheManagerServiceData();
        return mCacheManager;
    }

    public CacheManagerServiceData() {
        if (mGenericCache == null) {
            mGenericCache = new ConcurrentHashMap<String, String>();
        }
        if (mSessionCache == null) {
            mSessionCache = new ConcurrentHashMap<String, Session>();
        }
    }

    public void setSessionCache(Context _context, Session session)
    {
        String _sessionString = new Gson().toJson(session);

        mSessionCache.put(PREF_USERSESSION,session);
        Helper.putPrefString(_context,PREF_USERSESSION,_sessionString);
    }

    public Session getSessionCache(Context _context)
    {
        Session _session = mSessionCache.get(PREF_USERSESSION);
        if(_session == null)
        {
            _session = new Gson().fromJson(Helper.getPrefString(_context,PREF_USERSESSION),Session.class);
        }
        return _session;
    }

    public <T> void setGenericCache(Context _context, String name,T data)
    {
        String _dataString = new Gson().toJson(data);

        mGenericCache.put(name,_dataString);
        Helper.putPrefString(_context,name,_dataString);
    }

    public <T> T getGenericCache(Context _context, String name,Class<T> clazz)
    {
        T _session = new Gson().fromJson(mGenericCache.get(name),clazz);
        if(_session == null)
        {
            _session = new Gson().fromJson(Helper.getPrefString(_context,name),clazz);
        }
        return _session;
    }


    public <T> void addListDataToCache(List<T> cachedList, List<T> newList) {
        if (cachedList == null)
            cachedList = newList;
        else
            cachedList.addAll(newList);
    }

    public static void dropAllCacheData() {
        if (mGenericCache != null)
        {
            mGenericCache.clear();
        }

        if (mSessionCache != null)
        {
            mSessionCache.clear();
        }
    }
}