Ehcache: putIfAbsent: Insert when the key is not exist in the cache

org.ehcache.Cache#putIfAbsent method maps the specified key to the specified value in this cache, unless a non-expired mapping already exists. This method return the value to which the specified key was previously mapped,  or null if no such mapping existed or the mapping was expired

 

Signature

V putIfAbsent(K key, V value) throws CacheLoadingException, CacheWritingException;

 

This is equivalent to below code.

if (!cache.containsKey(key)){
	cache.put(key, value);
	return null;
}
else
	return cache.get(key);

Find the below working application.

 

CachePutIfAbsentDemo.java

package com.sample.app;

import java.util.Iterator;

import org.ehcache.Cache;
import org.ehcache.CacheManager;
import org.ehcache.Cache.Entry;
import org.ehcache.config.builders.CacheConfigurationBuilder;
import org.ehcache.config.builders.CacheManagerBuilder;
import org.ehcache.config.builders.ResourcePoolsBuilder;

public class CachePutIfAbsentDemo {

	private static void printAllElementsFromCache(Cache<Long, String> empCache) {
		System.out.println("\nPrint all the elements from the cache");

		Iterator<Entry<Long, String>> iter = empCache.iterator();

		while (iter.hasNext()) {
			Entry<Long, String> entry = iter.next();
			System.out.println(entry.getKey() + " is mapped to (" + entry.getValue() + ")");
		}

	}

	public static void main(String[] args) {
		CacheManager cacheManager = CacheManagerBuilder.newCacheManagerBuilder().build(true);

		Cache<Long, String> empCache = cacheManager.createCache("empCache", CacheConfigurationBuilder
				.newCacheConfigurationBuilder(Long.class, String.class, ResourcePoolsBuilder.heap(100)).build());

		empCache.put(1L, "Ram");
		empCache.put(2L, "Krishna");

		printAllElementsFromCache(empCache);

		System.out.println("\nInsert entries with keys 1 and 3 to the cache");

		String val1 = empCache.putIfAbsent(1L, "Rama Krishna");
		String val2 = empCache.putIfAbsent(3L, "Joel");
		
		System.out.println("val1: " + val1);
		System.out.println("val2: " + val2);

		printAllElementsFromCache(empCache);

	}

}

Output

Print all the elements from the cache
1 is mapped to (Ram)
2 is mapped to (Krishna)

Insert entries with keys 1 and 3 to the cache
val1: Ram
val2: null

Print all the elements from the cache
1 is mapped to (Ram)
2 is mapped to (Krishna)
3 is mapped to (Joel)

 

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