Java tutorial
/*
* Copyright 2008-2010 the T2 Project ant the Others.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//package org.t2framework.commons.util;
import java.lang.ref.WeakReference;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.atomic.AtomicReference;
public class LazyLoadingReference<T> {
protected Factory<T> factory;
protected AtomicReference<WeakReference<Future<T>>> reference = new AtomicReference<WeakReference<Future<T>>>();
public LazyLoadingReference(Factory<T> factory) {
this.factory = factory;
}
public T get() throws IllegalStateException {
while (true) {
WeakReference<Future<T>> ref = reference.get();
boolean valid = true;
if (ref == null) {
FutureTask<T> f = new FutureTask<T>(new Callable<T>() {
@Override
public T call() throws Exception {
return factory.create();
}
});
ref = new WeakReference<Future<T>>(f);
if (valid = reference.compareAndSet(null, ref)) {
f.run();
}
}
if (valid) {
try {
Future<T> f = ref.get();
if (f != null) {
return f.get();
} else {
reference.compareAndSet(ref, null);
}
} catch (CancellationException e) {
reference.compareAndSet(ref, null);
} catch (ExecutionException e) {
throw new IllegalStateException(e.getCause());
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
}
}
public interface Factory<T> {
T create() throws CancellationException, Exception;
}
}-------------------------
/*
* Copyright 2008-2009 the T2 Project ant the Others.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.t2framework.commons.util;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.CancellationException;
import org.t2framework.commons.cache.Cache;
import org.t2framework.commons.cache.CacheFactory;
import org.t2framework.commons.cache.CacheType;
import junit.framework.TestCase;
public class LazyLoadingReferenceTest extends TestCase {
public void test_loadSimple() throws Exception {
LazyLoadingReference<String> target = new LazyLoadingReference<String>(
new LazyLoadingReference.Factory<String>() {
public String create() {
return "hoge";
}
});
assertEquals("hoge", target.get());
}
public void test_loadSimple2() throws Exception {
LazyLoadingReference<Cache<String, String>> t2 = new LazyLoadingReference<Cache<String, String>>(
new LazyLoadingReference.Factory<Cache<String, String>>() {
@Override
public Cache<String, String> create() throws CancellationException {
Cache<String, String> c = CacheFactory.createCache(CacheType.DEFAULT);
c.put("aaa", "bbb");
return c;
}
});
Cache<String, String> cache = t2.get();
assertNotNull(cache);
assertNotNull(cache.get("aaa"));
}
public void test_exception() throws Exception {
final Exception e = new Exception();
LazyLoadingReference<String> target = new LazyLoadingReference<String>(
new LazyLoadingReference.Factory<String>() {
public String create() throws Exception {
throw e;
}
});
try {
target.get();
fail();
} catch (IllegalStateException t) {
assertNotNull(t.getCause());
assertTrue(t.getCause().getClass() == Exception.class);
assertEquals(e, t.getCause());
}
}
public void test_loadHeavy() throws Exception {
final LazyLoadingReference<String> target = new LazyLoadingReference<String>(
new LazyLoadingReference.Factory<String>() {
public String create() {
return "hoge";
}
});
final Random random = new Random(System.currentTimeMillis());
List<Thread> list = new ArrayList<Thread>();
for (int i = 0; i < 20; i++) {
Runnable r = new Runnable() {
public void run() {
try {
long l = random.nextLong() % 100;
Thread.sleep(l < 0 ? l * -1 : l);
assertEquals("hoge", target.get());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread t = new Thread(r);
list.add(t);
t.start();
}
for (Thread t : list) {
t.join();
}
}
}