com.squarespace.cldr.LazyLoader Maven / Gradle / Ivy
package com.squarespace.cldr;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
/**
* Lazy loader for classes, builds an instance on the first request.
*/
public class LazyLoader {
private final Map> classMap = new ConcurrentHashMap<>();
/**
* Gets a new instance of the class corresponding to the key.
*/
public V get(K key) {
Entry entry = classMap.get(key);
return entry == null ? null : entry.get();
}
/**
* Puts a class into the map.
*/
public void put(K key, Class cls) {
classMap.put(key, new Entry<>(cls));
}
private static class Entry {
private Class cls;
private AtomicReference ref;
private AtomicBoolean failure;
public Entry(Class cls) {
this.cls = cls;
this.ref = new AtomicReference<>();
this.failure = new AtomicBoolean();
}
/**
* Return the constructed value, or constructs a new one. If the creation
* of the instance fails, this entry is marked as failed and will not retry.
*/
public V get() {
if (failure.get()) {
return null;
}
V value = ref.get();
if (value != null) {
return value;
}
try {
value = cls.newInstance();
ref.lazySet(value);
return value;
} catch (InstantiationException | IllegalAccessException e) {
failure.set(true);
return null;
}
}
}
}