http://xmlgraphics.apache.org/fop/: Apache FOP (Formatting Objects Processor) is the world's first print formatter driven by XSL formatting objects (XSL-FO) and the world's first output independent formatter. It is a Java application that reads a formatting object (FO) tree and renders the resulting pages to a specified output. Output formats currently supported include PDF, PCL, PS, AFP, TIFF, PNG, SVG, XML (area tree representation), Print, AWT and TXT. The primary output target is PDF. (Apache Software Foundation) 
/*
 * 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.
 */

/* $Id$ */

package org.apache.fop.pdf;

import java.io.IOException;
import java.io.OutputStream;


Optional Content Group Dictionary, which we will call a 'layer'.

/**
 * Optional Content Group Dictionary, which we will call a 'layer'.
 */
public class PDFLayer extends PDFIdentifiedDictionary {

    public abstract static class Resolver {
        private boolean resolved;
        private PDFLayer layer;
        private Object extension;
        public Resolver(PDFLayer layer, Object extension) {
            this.layer = layer;
            this.extension = extension;
        }
        public PDFLayer getLayer() {
            return layer;
        }
        public Object getExtension() {
            return extension;
        }
        public void resolve() {
            if (!resolved) {
                performResolution();
                resolved = true;
            }
        }
        protected void performResolution() {
        }
    }

    private Resolver resolver;

    public PDFLayer(String id) {
        super(id);
        put("Type", new PDFName("OCG"));
    }

    @Override
    public int output(OutputStream stream) throws IOException {
        if (resolver != null) {
            resolver.resolve();
        }
        return super.output(stream);
    }

    public void setResolver(Resolver resolver) {
        this.resolver = resolver;
    }

    public void populate(Object name, Object intent, Object usage) {
        if (name != null) {
            put("Name", name);
        }
        if (intent != null) {
            put("Intent", intent);
        }
        if (usage != null) {
            put("Usage", usage);
        }
    }

}