com.sun.hk2.component.SoftCache Maven / Gradle / Ivy
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package com.sun.hk2.component;
import java.lang.ref.SoftReference;
import java.util.concurrent.Callable;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* A very primitive cache of at most one entry, that uses both SoftReference(s) to
* the key as well as the value it caches. Useful to provide minimal caching
* without imposing on heap.
*
* @author Jeff Trent
* @since 3.1
*/
public class SoftCache {
private Logger logger = Logger.getLogger(SoftCache.class.getName());
protected SoftReference key;
protected SoftReference value;
/**
* Returns either the cached value if hasn't been reclaimed by GC. Otherwise invokes
* the callable to refresh the cached value, and caching it again in the process.
*
* @param key the key; must be non-null
* @param callable the callable in case the cache is empty; must be non-null
* @return the value (either from cache or populated by the callable as a last resort)
*/
public synchronized V get(K k, Callable callable) {
assert(null != callable);
K thisK = (null == key) ? null : key.get();
if (k.equals(thisK)) {
if (null == value) {
return usingCacheValue(null);
} else {
V thisV = value.get();
if (null != thisV) {
return usingCacheValue(thisV);
}
}
}
key = new SoftReference(k);
try {
V thisV = callable.call();
return cacheValue(value, thisV);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
protected V cacheValue(SoftReference value2, V thisV) {
if (null == thisV) {
value = null;
} else {
value = new SoftReference(thisV);
}
logger.log(Level.FINEST, "caching value");
return thisV;
}
protected V usingCacheValue(V thisV) {
logger.log(Level.FINEST, "using cached value");
return thisV;
}
/**
* Clears the cache
*/
public void clear() {
logger.log(Level.FINEST, "clearing cached value");
key = null;
value = null;
}
}