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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.tools.ant.types.resources;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import org.apache.tools.ant.types.Resource;
/**
* Resource collection which load underlying resource collection only on demand
* with support for caching
*/
public class LazyResourceCollectionWrapper extends
AbstractResourceCollectionWrapper {
/** List of cached resources */
private final List<Resource> cachedResources = new ArrayList<Resource>();
private FilteringIterator filteringIterator;
@Override
protected Iterator<Resource> createIterator() {
Iterator<Resource> iterator;
if (isCache()) {
if (filteringIterator == null) {
// no worry of thread safety here, see function's contract
filteringIterator = new FilteringIterator(
getResourceCollection().iterator());
}
iterator = new CachedIterator(filteringIterator);
} else {
iterator = new FilteringIterator(getResourceCollection().iterator());
}
return iterator;
}
@Override
protected int getSize() {
// to compute the size, just iterate: the iterator will take care of
// caching
final Iterator<Resource> it = createIterator();
int size = 0;
while (it.hasNext()) {
it.next();
size++;
}
return size;
}
/**
* Specify if the resource should be filtered or not. This function should
* be overrided in order to define the filtering algorithm
*
* @param r resource considered for filtration
* @return whether the resource should be filtered or not
*/
protected boolean filterResource(final Resource r) {
return false;
}
private class FilteringIterator implements Iterator<Resource> {
Resource next = null;
boolean ended = false;
protected final Iterator<Resource> it;
public FilteringIterator(final Iterator<Resource> it) {
this.it = it;
}
public boolean hasNext() {
if (ended) {
return false;
}
while (next == null) {
if (!it.hasNext()) {
ended = true;
return false;
}
next = it.next();
if (filterResource(next)) {
next = null;
}
}
return true;
}
public Resource next() {
if (!hasNext()) {
throw new UnsupportedOperationException();
}
final Resource r = next;
next = null;
return r;
}
public void remove() {
throw new UnsupportedOperationException();
}
}
/**
* Iterator that will put in the shared cache array list the selected
* resources
*/
private class CachedIterator implements Iterator<Resource> {
int cusrsor = 0;
private final Iterator<Resource> it;
/**
* Default constructor
*
* @param it
* the iterator which will provide the resources to put in
* cache
*/
public CachedIterator(final Iterator<Resource> it) {
this.it = it;
}
public boolean hasNext() {
synchronized (cachedResources) {
// have we already cached the next entry ?
if (cachedResources.size() > cusrsor) {
return true;
}
// does the wrapped iterator any more resource ?
if (!it.hasNext()) {
return false;
}
// put in cache the next resource
final Resource r = it.next();
cachedResources.add(r);
}
return true;
}
public Resource next() {
// first check that we have some to deliver
if (!hasNext()) {
throw new NoSuchElementException();
}
synchronized (cachedResources) {
// return the cached entry as hasNext should have put one for
// this iterator
return cachedResources.get(cusrsor++);
}
}
public void remove() {
throw new UnsupportedOperationException();
}
}
}
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