nz.org.take.DefaultKnowledgeBase.java Source code

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Here is the source code for nz.org.take.DefaultKnowledgeBase.java

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/**
 * Copyright 2007 Jens Dietrich Licensed 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 nz.org.take;

import java.util.*;

import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.collections.ListUtils;

/**
 * Default implementation of knowledge base.
 * Access to instance variables is synchronized, i.e. this class is thread safe.
 * @author <a href="http://www-ist.massey.ac.nz/JBDietrich/">Jens Dietrich</a>
 */

public class DefaultKnowledgeBase extends AbstractAnnotatable implements KnowledgeBase {
    private List<KnowledgeElement> elements = new ArrayList<KnowledgeElement>();
    private List<Query> queries = new ArrayList<Query>();
    private Map<String, KnowledgeElement> elementsById = new HashMap<String, KnowledgeElement>();

    /**
     * Retrieve knowledge by id.
     * @param id an id
     * @return a knowledge element
     */
    public synchronized KnowledgeElement getElement(String id) {
        return this.elementsById.get(id);
    }

    /**
     * Retrieve knowledge by predicate.
     * @param p the predicate
     * @return knowledge elements
     */
    public synchronized List<KnowledgeElement> getElements(final Predicate p) {
        org.apache.commons.collections.Predicate filter = new org.apache.commons.collections.Predicate() {
            public boolean evaluate(Object arg) {
                KnowledgeElement e = (KnowledgeElement) arg;
                return p.equals(e.getPredicate());
            }
        };
        return (List<KnowledgeElement>) CollectionUtils.select(this.elements, filter);
    }

    /**
     * Get all elements.
     * @return knowledge elements
     */
    public synchronized List<KnowledgeElement> getElements() {
        return (List<KnowledgeElement>) ListUtils.unmodifiableList(this.elements);
    }

    /**
     * Get all predicates for which knowledge elements are available.
     * @return predicates
     */
    public synchronized Collection<Predicate> getSupportedPredicates() {
        Set<Predicate> predicates = new HashSet<Predicate>();
        for (KnowledgeElement e : this.elements) {
            predicates.add(e.getPredicate());
        }
        return predicates;
    }

    /**
     * Add an element.
     * @param e an element
     */
    public synchronized void add(KnowledgeElement e) {
        this.elements.add(e);
        this.elementsById.put(e.getId(), e);
    }

    /**
     * Remove an element, return true if this succeeded.
     * @param e an element
     * @return a boolean
     */
    public synchronized boolean remove(KnowledgeElement e) {
        boolean result = this.elements.remove(e);
        result = result && (null != this.elementsById.remove(e.getId()));
        return result;
    }

    /**
     * Add a query.
     * @param q a query
     */
    public synchronized void add(Query q) {
        this.queries.add(q);
    }

    /**
     * Remove  a query, return true if this succeeded.
     * @param q  a query
     * @return a boolean
     */
    public synchronized boolean remove(Query q) {
        return this.queries.remove(q);
    }

    /**
     * Get all queries.
     * @return queries
     */
    public List<Query> getQueries() {
        return (List<Query>) ListUtils.unmodifiableList(this.queries);
    }

    public void accept(KnowledgeBaseVisitor visitor) {
        if (visitor.visit(this)) {
            for (Query q : queries)
                q.accept(visitor);
            for (KnowledgeElement e : elements)
                e.accept(visitor);
        }
        visitor.endVisit(this);
    }

    /**
     * Get a knowledge base.
     * @return a knowledge base
     */
    public KnowledgeBase getKnowledgeBase() throws TakeException {
        return this;
    }
}