org.zkoss.bind.paranamer.CachingParanamer Maven / Gradle / Ivy
/***
*
* Copyright (c) 2007 Paul Hammant
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.zkoss.bind.paranamer;
import java.lang.reflect.AccessibleObject;
import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
/**
* Implementation of Paranamer which delegate to another Paranamer implementation,
* adding caching functionality to speed up usage. It also uses a WeakHashmap as
* an implementation detail (wrapped in Collections.synchronizedMap(..)), to allow
* large usages to garbage collect things as big as whole classloaders (after
* working through all the refs that originated from that classloader). Tomcat and
* other 'containers' do this during hot application deployment, undeployment and
* most importantly for Paranamer redeployment. Basically, this will allow a
* perm-gen usage keeps growing scenario.
*
* @author Paul Hammant
* @author Mauro Talevi
*/
public class CachingParanamer implements Paranamer {
private final Paranamer delegate;
private final Map methodCache = makeMethodCache();
protected Map makeMethodCache() {
return Collections.synchronizedMap(new WeakHashMap());
}
/**
* Specify a Paranamer instance to delegates to.
* @param delegate the paranamer instance to use
*/
public CachingParanamer(Paranamer delegate) {
this.delegate = delegate;
}
public String[] lookupParameterNames(AccessibleObject methodOrConstructor) {
return lookupParameterNames(methodOrConstructor, true);
}
public String[] lookupParameterNames(AccessibleObject methodOrCtor, boolean throwExceptionIfMissing) {
String[] names = methodCache.get(methodOrCtor);
// refer PARANAMER-19
if (names == null) {
names = delegate.lookupParameterNames(methodOrCtor, throwExceptionIfMissing);
methodCache.put(methodOrCtor, names);
}
return names;
}
/**
* This implementation has a better concurrent design (ConcurrentHashMap) which
* has a better strategy to implement concurrency: segments instead of synchronized.
*
* It also drops the underlying WeakHashMap implementation as that can't work with
* ConcurrentHashMap with some risk of growing permgen for a certain class of usage.
*
* So instead of wrapping via 'Collections.synchronizedMap(new WeakHashMap())' we now
* have 'new ConcurrentHashMap()'
*
*/
public static class WithoutWeakReferences extends CachingParanamer {
public WithoutWeakReferences(Paranamer delegate) {
super(delegate);
}
@Override
protected Map makeMethodCache() {
return new ConcurrentHashMap();
}
}
}