last.java

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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.Iterator;
import java.util.ArrayList;
import java.util.Collection;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.types.ResourceCollection;

/**
 * ResourceCollection that contains the last <code>count</code> elements of
 * another ResourceCollection, a la the UNIX tail command.
 * @since Ant 1.7.1
 */
public class Last extends SizeLimitCollection {

    /**
     * Take the last <code>count</code> elements.
     * @return a Collection of Resources.
     */
    protected Collection getCollection() {
        int count = getValidCount();
        ResourceCollection rc = getResourceCollection();
        int i = count;
        Iterator iter = rc.iterator();
        int size = rc.size();
        for (; i < size; i++) {
            iter.next();
        }

        ArrayList al = new ArrayList(count);
        for (; iter.hasNext(); i++) {
            al.add(iter.next());
        }
        int found = al.size();
        if (found == count || (size < count && found == size)) {
            return al;
        }

        //mismatch:
        String msg = "Resource collection " + rc + " reports size " + size
            + " but returns " + i + " elements.";

        //size was understated -> too many results; warn and continue:
        if (found > count) {
            log(msg, Project.MSG_WARN);
            return al.subList(found - count, found);
        }
        //size was overstated; we missed some and are now in error-land:
        throw new BuildException(msg);
    }

}