为什么在尝试获取PDFFile实例的页面时会出现PDFParseException？

Question

我正在使用PDFRenderer版本0.9.1在ColdFusion中以编程方式将PDF转换为PNG。

这是我写的UDF：

<cffunction
    name="pdfToImageFile"
    returntype="String"
    output="false"
    hint="Converts a phsyical PDF File to a physical Image file and returns the absolute path of the new Image file">
    <cfargument name="sourcePath" type="String" default="" />
    <cfargument name="destinationPath" type="String" default="" />
    <cfargument name="format" type="String" default="png" />

    <cfset var LOCAL = {} />

    <cfif NOT isValidPDF(Trim(ARGUMENTS.sourcePath))>
        <cfthrow
            message="Source file not specified or not a valid PDF file." />
    </cfif>

    <cfif NOT DirectoryExists(Trim(ARGUMENTS.destinationPath))>
        <cfthrow message="Inavlid Destination path." />
    </cfif>

    <cfif
        NOT ListFindNoCase(
                GetWriteableImageFormats(),
                Trim(ARGUMENTS.format)
                )>
        <cfthrow message="Inavlid Image format specified." />
    </cfif>

    <cfscript>
        LOCAL.DestinationFilePath =
                Trim(ARGUMENTS.destinationPath)
            &   "\"
            &   REQUEST.UDFLib.File.getFileNameWithoutExtension(
                    GetFileFromPath(ARGUMENTS.sourcePath)
                    )
            &   "."
            &   LCase(Trim(ARGUMENTS.format));

        LOCAL.RandomAccessFile =
            CreateObject(
                "java",
                "java.io.RandomAccessFile"
                ).init(
                    CreateObject(
                        "java",
                        "java.io.File"
                        ).init(ARGUMENTS.sourcePath),
                    "r"
                    );

        LOCAL.FileChannel = LOCAL.RandomAccessFile.getChannel();

        LOCAL.PDFFile =
            CreateObject(
                "java",
                "com.sun.pdfview.PDFFile"
                ).init(
                    LOCAL.FileChannel.map(
                        CreateObject(
                            "java",
                            "java.nio.channels.FileChannel$MapMode"
                            ).READ_ONLY,
                        0,
                        LOCAL.FileChannel.size()
                        )
                    ) />

        LOCAL.PDFPage = LOCAL.PDFFile.getPage(1) />

        //  The following line throws an exception "Element PDFPAGE is undefined in LOCAL." 
        LOCAL.Rectangle = LOCAL.PDFPage.getBBox();

        LOCAL.BufferedImage =
            CreateObject(
                "java",
                "java.awt.image.BufferedImage"
                ).init(
                    LOCAL.Rectangle.width,
                    LOCAL.Rectangle.height,
                    CreateObject(
                        "java",
                        "java.awt.image.BufferedImage"
                        ).TYPE_INT_RGB
                    );

        LOCAL.Graphics = LOCAL.BufferedImage.createGraphics();

        LOCAL.Graphics.drawImage(
            LOCAL.PDFPage.getImage(
                LOCAL.Rectangle.width,
                LOCAL.Rectangle.height,
                LOCAL.Rectangle,
                JavaCast("null", ""),
                true,
                true
                ),
            0,
            0,
            JavaCast("null", "")
            );

        LOCAL.Graphics.dispose();

        LOCAL.ImageFile =
            CreateObject(
                "java",
                "java.io.File"
                ).init(LOCAL.DestinationFilePath);

        //  Delete existing image file
        if  (LOCAL.ImageFile.exists())
            LOCAL.ImageFile.delete();

        //  Export the image to the specified format
        CreateObject(
            "java",
            "javax.imageio.ImageIO"
            ).write(
                LOCAL.BufferedImage,
                JavaCast("string", Trim(ARGUMENTS.format)),
                LOCAL.ImageFile
                );

        LOCAL.RandomAccessFile.close();

        return LOCAL.DestinationFilePath;
    </cfscript>
</cffunction>

这适用于我投入的大多数PDF。但是，它偶尔会抛出某些PDF的例外（所有PDF都是专有的，不能共享）。

尝试使用PDFFile.getPage(1)引用PDF的第一页时，我收到ColdFusion异常：Element PDFPAGE is undefined in LOCAL.。

我通过调试器运行了这个，经过深入检查，我看到了某个PDF的以下值：

PDFFile.getNumPages() : 0
PDFFile.getVersionString() : 1.7
PDFFile.getRoot() : 
    Indirect to #182
    Catalog dictionary. Keys:
       StructTreeRoot  Indirect to #40com.sun.pdfview.PDFParseException: Could not decrypt: Need at least 2880 bytes of space in output buffer
       Pages  Indirect to #178com.sun.pdfview.PDFParseException: Could not decrypt: Need at least 80 bytes of space in output buffer
       Type  Name: /Catalog
       ViewerPreferences  Untyped dictionary. Keys:
       Direction  Name: /L2R
       Metadata  Indirect to #23
    Caught an error: com.sun.pdfview.PDFParseException: Could not decrypt: Need at least 2672 bytes of space in output buffer
       MarkInfo  Untyped dictionary. Keys:
       Marked  Boolean: true

我不熟悉Java，所以我不知道这一切意味着什么，但它让我相信PDF格式错误，无法正确阅读Java库。

知道究竟是什么原因造成这类错误？可能是因为PDF是如何生成/制作的，是一个与PDFRenderer库不兼容的较新版本？