com.intelligentsia.dowsers.entity.view.processor.Projection.java Source code

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Here is the source code for com.intelligentsia.dowsers.entity.view.processor.Projection.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 com.intelligentsia.dowsers.entity.view.processor;

import java.util.Iterator;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.intelligentsia.dowsers.entity.Entity;

/**
 * Projection.
 * 
 * @author <a href="mailto:jguibert@intelligents-ia.com" >Jerome Guibert</a>
 */
public final class Projection extends ProcessorUnit {

    private final ImmutableSet<String> attributeNames;

    /**
     * The string form of this {@link Projection}.
     * 
     * @serial
     */
    public volatile String value = null;

    /**
     * Build a new instance of Projection.
     * 
     * @param processor
     *            {@link Processor} instance
     * @param attributeNames
     *            set of attribute name
     * @throws NullPointerException
     *             if one of parameters is null
     * @throws IllegalStateException
     *             if no output attribute was specified
     */
    public Projection(final Processor processor, final ImmutableSet<String> attributeNames)
            throws NullPointerException, IllegalStateException {
        super(processor);
        this.attributeNames = Preconditions.checkNotNull(attributeNames);
        Preconditions.checkState(!attributeNames.isEmpty());
        defineString();
    }

    @Override
    public Item apply(final Entity input) {
        final Item item = super.apply(input);
        if (item != null) {
            // must we do a local copy of this set ?
            final Iterator<String> iterator = Sets.difference(item.keySet(), attributeNames).iterator();
            while (iterator.hasNext()) {
                item.remove(iterator.next());
            }
        }
        return item;
    }

    @Override
    public String toString() {
        return defineString();
    }

    /**
     * Build inner value.
     */
    private String defineString() {
        if (value != null) {
            return value;
        }
        final StringBuilder builder = new StringBuilder("(projection ").append(super.toString()).append(" ");
        final Iterator<String> iterator = attributeNames.iterator();
        while (iterator.hasNext()) {
            builder.append(iterator.next()).append(" ");
        }
        value = builder.append(")").toString();
        return value;

    }
}