javapersistenceehcacheehcache-2

ehcache persist to disk issues


I want to do something with ehcache in Java that I think should be extremely simple, but I've spent enough time frustrating myself with the docs...

  1. Write a value to a disk persistent cache. Shut down.

  2. Start up again and read that value.

Here is my Java function:

private static void testCacheWrite() {

  // create the cache manager from our configuration
  URL url = TestBed.class.getClass().getResource("/resource/ehcache.xml");
  CacheManager manager = CacheManager.create(url);
  // check to see if our cache exits, if it doesn't create it
  Cache testCache = null;
  if (!manager.cacheExists("test")) {
    System.out.println("No cache found. Creating cache...");
    int maxElements = 50000;
    testCache = new Cache("test", maxElements,
      MemoryStoreEvictionPolicy.LFU, true, null, true, 60, 30,
      true, Cache.DEFAULT_EXPIRY_THREAD_INTERVAL_SECONDS, null);
    manager.addCache(testCache);
    // add an element to persist
    Element el = new Element("key", "value");
    testCache.put(el);
    testCache.flush();
    System.out.println("Cache to disk. Cache size on disk: " +
      testCache.getDiskStoreSize());
  } else {
    // cache exists so load it
    testCache = manager.getCache("test");
    Element el = testCache.get("key");
    if (null == el) {
      System.out.print("Value was null");
      return;
    }
    String value = (String) el.getObjectValue();
    System.out.println("Value is: " + value);
  }
  manager.shutdown();
}

And here is my cache configuration (ehcache.xml):

<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
  <diskStore path="C:/mycache"/><!-- java.io.tmpdir -->
  <defaultCache
    maxElementsInMemory="10000"
    eternal="true"
    timeToIdleSeconds="120"
    timeToLiveSeconds="120"
    overflowToDisk="true"
    maxElementsOnDisk="10000000"
    diskPersistent="true"
    diskExpiryThreadIntervalSeconds="120"
    memoryStoreEvictionPolicy="LRU" />
</ehcache>

Even though I see test.index and test.data files on disk after the first run, output from this function is always the following (it never seems to load the cache from disk):

No cache found. Creating cache...
Cache to disk. Cache size on disk: 2

I must be doing something dumb here, but I 'm not sure what!


Solution

  • Okay, well what I did to fix this was configure my cache using the configuration file. Here is the updated config:

    <ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
             xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
    
        <diskStore path="C:/mycache" />
    
        <defaultCache
            maxElementsInMemory="10000" 
            eternal="true"
            timeToIdleSeconds="120" 
            timeToLiveSeconds="120" 
            overflowToDisk="true"
            maxElementsOnDisk="10000000" 
            diskPersistent="true"
            diskExpiryThreadIntervalSeconds="120" 
            memoryStoreEvictionPolicy="LRU" />
    
        <cache 
            name="test" 
            maxElementsInMemory="500" 
            eternal="true"
            overflowToDisk="true" 
            timeToIdleSeconds="300" 
            timeToLiveSeconds="600"
            diskPersistent="true" 
            diskExpiryThreadIntervalSeconds="1"
            memoryStoreEvictionPolicy="LFU" />
    
    </ehcache>
    

    So basically I didn't use the constructor to define the cache.

    I suppose this will work, but I still wonder why programatically defined caches can't persist on disk (especially since they are still written to disk!).

    Thanks for the comments guys.