Remove Data from Cache

NCache provides a Remove and a Delete method for removal of an object from the cache. The difference between the Delete method and Remove method is stated below:

• Delete returns void after deletion of the item from the cache.
• Remove deletes the data from the cache and returns the deleted item.

For Delete/Remove API calls, if a backing source is configured and Write-through is enabled, all the keys passed onto the Cache via the API will first be looked into and deleted from the Cache and irrespective of the key mapping, the call will be forwarded to the backing source.

Pre-Requisites

• Add the following Maven dependencies in your pom.xml file:

<dependency>
    <groupId>com.alachisoft.ncache</groupId>
    <artifactId>ncache-client</artifactId>
    <version>5.2.0</version>
</dependency>

• Import the following packages in your application:
  • import javax.cache.CacheManager;
  • import javax.cache.Caching;
  • import javax.cache.spi.CachingProvider;
• Make sure that the data is serailized or registered with NCache Compact Serialization format.
• Make sure that the cache is running.

Using Remove Method

The Remove method deletes the key from the cache and returns the deleted object to the application, where NCache’s JCache API provider remove method behaves as per JCache’s specifications.

try
{
    String key = "Product:1001";
    Product product = null;
    // False is returned if key does not exist in cache
    Boolean result = cache.remove(key);
    if (result != true) 
    {
        //Deleted.  
    } 
    else 
    { 
        //Failed.
    }
}
catch(Exception ex)
{
    // Handle Exception
}

Using Delete Method

The Delete method deletes the key from the cache. You will need to get NCache API’s cache instance in order to perform this operation.

try
{
    // Specify the key to be deleted
    String key = "Product:1001";

    // Delete the key from the cache
    cache.delete(key);
}
catch(Exception ex)
{
    // Handle Exception 
}

Remove Bulk Data from Cache

Just like the atomic remove operation, removeAll also returns removed items. Here the removed items are returned in the form of a HashMap, however NCache's JCache API’s removeAll method can also be used for deleting items in bulk, which behaves as Oracle documents it.

For both, the atomic and the bulk Delete/Remove API calls, if a backing source is configured and Write-through is enabled, all the keys passed onto the Cache via the API will first be looked into and deleted from the Cache and irrespective of the key mapping, the call will be forwarded to the backing source.

try
{
    Product product1 = null, product2 = null;
    String[] keys = {"Product:1001", "Product:1002"};
    CacheItem[] items = new CacheItem[2];
    items[0] = new CacheItem(product1);
    items[1] = new CacheItem(product2);
    HashMap map = new HashMap();
    for (int i = 0; i < 2; i++) 
    {
        map.put(keys[i], items[i]);
    }   
    jCache.removeAll(map.keySet());
}
catch(Exception ex)
{
    // Handle Exception
}

Remove Items from Cache Asynchronously

NCache provides the AsyncItemRemovedCallback interface to be used in order to receive notification upon completion of item removal. Add the following package in your application to utilize this API.

try
{
    String key = "Product:1001";
    EventListener listener = new EventListener();
    cache.removeAsync(key, (AsyncItemRemovedCallback) listener,  DSWriteOption.None, null);
}
catch(Exception ex)
{
    // Handle Exception
}

Create a callback to register the events for the items removed from the cache asynchronously.

public class EventListener implements AsyncItemRemovedCallback
   {
@Override
      public void asyncItemRemoved(String string, Object o) 
      {

        if(o.toString().equals("Success"))
        {
          // do something
        }
        if(o.toString().equals("Failure"))
        {
          // do something
        }
        if(o instanceof Exception)
        {
          // do something
        }
    }
}

See Also

Initialize Cache Add/Update in Cache
Clear Cache
Hibernate Caching
NCache Java Session Module