What is Ehcache

Ehcache is an open source, standards-based cache that boosts performance, offloads your database, and simplifies scalability. It’s Java-based.

Usage

In order to use Ehcache, developer need to configure CacheManager and initialize it, then create Cache.

This can be achieved by programmatic configuration or xml.

Ehcache version is 3.4 in this post.

By XML

<config xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
	xmlns='http://www.ehcache.org/v3'
	xsi:schemaLocation="http://www.ehcache.org/v3 http://www.ehcache.org/schema/ehcache-core.xsd">

    <cache alias="foo">
        <key-type>java.lang.String</key-type>
	<value-type>java.lang.String</value-type>
	<resources>
	    <heap unit="entries">2000</heap>
	    <offheap unit="MB">500</offheap>
	</resources>
    </cache>

    <cache-template name="numberTemplate">
	<key-type>java.lang.Integer</key-type>
	<value-type>java.lang.Integer</value-type>
	<heap unit="entries">10</heap>
    </cache-template>
  
  <cache alias="bar" uses-template="numberTemplate"> 
    <key-type>java.lang.Number</key-type>
  </cache>

  <cache alias="simpleCache" uses-template="numberTemplate" />

</config>

• The key and value of cache foo are declared as String, if not specified, default is Object
• foo is declared to hold up to 2000 entries on heap
• foo is configured up to 500 MB off-heap memory before it starts evicting
• <cache-template> lets developer create an abstract configuration that further <cache> configurations can then extend
• bar is a such a cache which using the <cache template> named numberTemplate and overrides its key-type to Number

    URL myUrl = Test.class.getResource("/ehcache.xml");
    XmlConfiguration xmlConfig = new XmlConfiguration(myUrl); 
    CacheManager myCacheManager = CacheManagerBuilder.newCacheManager(xmlConfig);
		
    myCacheManager.init();
		
    Calculator calculator = new Calculator();
    calculator.setCache(myCacheManager.getCache("simpleCache", Integer.class, Integer.class));

By program

public class CacheHelper {

    private CacheManager cacheManager;
    private Cache<Integer, Integer> cache;

    public CacheHelper() {
		
	cacheManager = CacheManagerBuilder.newCacheManagerBuilder().build();
    
	cacheManager.init();

	cache = cacheManager.createCache("simpleCache", CacheConfigurationBuilder
				.newCacheConfigurationBuilder(Integer.class, Integer.class, ResourcePoolsBuilder.heap(10)));
    }

  //setter and getter
}

public class Calculator {

    private Cache<Integer, Integer> cache;

    public int getResult(int input) {
		
        if (cache.containsKey(input)) {
			
	    return (int) cache.get(input);
        }

        System.out.println("Calculating value of " + input + " and caching result.");

        int result = input * 2;
	
        cache.put(input, result);

        return result;
    }

  .....
}

Ehcache vs Redis

1. Ehcache is java-based, while redis is c-based
2. Redis can be accessed using the network and from a lot of programming language, while Ehcache cannot
3. Ehcache can be setup by simply including the jar, no additional installation steps are required, which Redis not.
4. Ehcache runs in the same process with the application, so it’s fast, no additional service is required to run.

About the performance, please refert to this article