/*
* JBoss, Home of Professional Open Source.
* Copyright 2000 - 2008, Red Hat Middleware LLC, and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
* distribution for a full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.cache.commands.read;
import org.jboss.cache.Fqn;
import org.jboss.cache.InvocationContext;
import org.jboss.cache.NodeSPI;
import org.jboss.cache.commands.Visitor;
/**
* Checks whether a given node exists in current in-memory state of the cache.
* Does not acquire any locks in doing so (result may be dirty read). Does
* not attempt to load nodes from a cache loader (may return false if a
* node has been evicted).
* <p/>
* Specifically used by the {@link org.jboss.cache.loader.ClusteredCacheLoader} to
* implement {@link org.jboss.cache.loader.CacheLoader#exists(org.jboss.cache.Fqn)}
* <p/>
* This is the equivalent of the old MethodCallDefinitions.existsMethod method call from 2.1.x.
* <p/>
*
* @author Mircea.Markus@jboss.com
* @since 2.2.0
*/
public class ExistsCommand extends AbstractDataCommand
{
public static final int METHOD_ID = 16;
public ExistsCommand(Fqn fqn)
{
this.fqn = fqn;
}
public ExistsCommand()
{
}
/**
* Checks whether a node represented by a given Fqn exists.
* Deleted and invalid nodes are not considered.
*
* @return true if the node exists, false otherwise.
*/
public Object perform(InvocationContext ctx)
{
NodeSPI node = ctx.lookUpNode(fqn);
return node != null && !node.isDeleted();
}
public Object acceptVisitor(InvocationContext ctx, Visitor visitor) throws Throwable
{
return visitor.visitExistsNodeCommand(ctx, this);
}
public int getCommandId()
{
return METHOD_ID;
}
}