cosnull.java

非常有用的操作pdf文件的java源码

/**
 * Copyright (c) 2003-2004, www.pdfbox.org
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
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 *    this list of conditions and the following disclaimer.
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 *    software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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package org.pdfbox.cos;



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

import org.pdfbox.exceptions.COSVisitorException;

/**
 * This class represents a null PDF object.
 *
 * @author <a href="mailto:[e-mail]">Ben Litchfield</a>
 * @version $Revision: 1.13 $
 */
public class COSNull extends COSBase
{
    /**
     * The null token.
     */
    public static final byte[] NULL_BYTES = new byte[] {110, 117, 108, 108}; //"null".getBytes( "ISO-8859-1" );
    
    /**
     * The one null object in the system.
     */
    public static final COSNull NULL = new COSNull();

    /**
     * Constructor.
     */
    private COSNull()
    {
        //limit creation to one instance.
    }

    /**
     * visitor pattern double dispatch method.
     *
     * @param visitor The object to notify when visiting this object.
     * @return any object, depending on the visitor implementation, or null
     * @throws COSVisitorException If an error occurs while visiting this object.
     */
    public Object accept( ICOSVisitor  visitor ) throws COSVisitorException
    {
        return visitor.visitFromNull( this );
    }
    
    /**
     * This will output this string as a PDF object.
     *  
     * @param output The stream to write to.
     * @throws IOException If there is an error writing to the stream.
     */
    public void writePDF( OutputStream output ) throws IOException
    {
        output.write(NULL_BYTES);
    }
}