org.cache2k.processor

Interface EntryProcessor<K,V,R>

public interface EntryProcessor<K,V,R>

An invokable function to perform an atomic operation on a cache entry. The entry processor is called via Cache.invoke(K, org.cache2k.processor.EntryProcessor<K, V, R>) or Cache.invokeAll(java.lang.Iterable<? extends K>, org.cache2k.processor.EntryProcessor<K, V, R>).

With the entry processor it is possible to realize arbitrary operation semantics for an entry. For example, the method Cache.replaceIfEquals(K, V, V) can be expressed with the entry processor as follows:

 

    public boolean replaceIfEquals(final K key, final V oldValue, final V newValue) {
      EntryProcessor<K, V, Boolean> p = new EntryProcessor<K, V, Boolean>() {
        public Boolean process(MutableCacheEntry<K, V> entry) {
          if (!entry.exists()) {
            return false;
          }
          if (oldValue == null) {
            if (null != entry.getValue()) {
              return false;
            }
          } else {
            if (!oldValue.equals(entry.getValue())) {
              return false;
            }
          }
          entry.setValue(newValue);
          return true;
        }
      };
      return cache.invoke(key, p);
    }
 

For effects on the loader and writer and further details consult the documentation on the MutableCacheEntry

Author:

Jens Wilke

See Also:

MutableCacheEntry, Cache.invoke(K, org.cache2k.processor.EntryProcessor<K, V, R>), Cache.invokeAll(java.lang.Iterable<? extends K>, org.cache2k.processor.EntryProcessor<K, V, R>)

Method Summary

Modifier and Type	Method and Description
R	process(MutableCacheEntry<K,V> entry) Examines or mutates an entry.

Method Detail

process

R process(MutableCacheEntry<K,V> entry)
   throws Exception

Examines or mutates an entry.

Important: The method must not have any side effects except on the processed entry. For one call to Cache.invoke(K, org.cache2k.processor.EntryProcessor<K, V, R>) the method might be called several times. Some methods of MutableCacheEntry throw exceptions that are consumed by the cache to do asynchronous processing.

Caveat about modification time and expiry: The point in time of the last modification, in case the entry is modified, is after the method completes. It is possible to set an alternative time with MutableCacheEntry.setRefreshedTime(long)

The cache is only modified, if the method completes without exception.

Parameters:

entry - the entry to examine or mutate. The reference is only valid within a method call

Returns:

a user defined result, that will be passed through and returned

Throws:

Exception - an arbitrary exception that will be wrapped into a EntryProcessingException. If an exception happens no modifications the cache content will not be altered.