In-Memory Caching

public class Cache {  
   private static final long MAX_SIZE = 100;  
   private final ConcurrentHashMap  map;  
   
   public Cache() {    
      map = new ConcurrentHashMap  ();  
   }  
   
   public String getEntry(String key) {    
      String result = createCacheEntry(key);    
      removeOldestCacheEntryIfNecessary();    
      return result;  
   }  
   
   private String createCacheEntry(String key) {    
      String result = map.get(key);    
      if (result == null) {      
         String putResult = map.putIfAbsent(key, createRandom());      
         if (putResult != null) {        
            result = putResult;      
         }   
      }    
      return result;  
   }  
   
   private void removeOldestCacheEntryIfNecessary() {    
      if (map.size() > MAX_SIZE) {      
         String keyToDelete = map.keys().nextElement();      
         map.remove(keyToDelete);    
      }  
   }  
   
   private String createRandom() {    
      return "I am resource which you want to cache...!!!!!";  
   }
}

public class Cache {  
   private static final long MAX_SIZE = 100;  
   private final LoadingCache  cache;  
   
   public Cache() {    
      cache = CacheBuilder.newBuilder().maximumSize(MAX_SIZE).build(
         new CacheLoader  () {
            @Override      
            public String load(String key) throws Exception {        
               return createRandom();      
            }    });  
   }  
   
   public String getEntry(String key) {    
       return cache.getUnchecked(key);  
   }  
   
   private String createRandom() {   
      return "I am resource which you want to cache...!!!!!";  
   }
}

public class CaffeineConfiguration {  
   private static final long MAX_SIZE = 100;  
   private static final long TTL = 30;  
   
   @Bean  
   public Caffeine caffeineConfig() {    
      return Caffeine.newBuilder().maximumSize(MAX_SIZE).expireAfterWrite(TTL, TimeUnit.MINUTES);  
   }  
   
   @Bean(name = "caffeineCacheManager")  
   public CacheManager caffeineCacheManager(Caffeine caffeine) {    
       CaffeineCacheManager caffeineCacheManager = new CaffeineCacheManager();    
       caffeineCacheManager.setCaffeine(caffeine);    
       return caffeineCacheManager;  
   }
}

public class Cache {

   @Cacheable(value = "cacheName", key = "#key", cacheManager = "caffeineCacheManager")  
   public String getEntry(String key) {   
      createRandom();  
   }  
   
   private String createRandom() {    
      return "I am resource which you want to cache...!!!!!"; 
   }
}