ghost4j class cast exception during joining two PostScripts

Question

I am trying to join two PostScript files to one with ghost4j 0.5.0 as follows:

final PSDocument[] psDocuments = new PSDocument[2];
psDocuments[0] = new PSDocument();
psDocuments[0].load("1.ps");
psDocuments[1] = new PSDocument();
psDocuments[1].load("2.ps");
psDocuments[0].append(psDocuments[1]);
psDocuments[0].write("3.ps");

During this simplified process I got the following exception message for the above "append" line:

org.ghost4j.document.DocumentException: java.lang.ClassCastException:   
org.apache.xmlgraphics.ps.dsc.events.UnparsedDSCComment cannot be cast to 
org.apache.xmlgraphics.ps.dsc.events.DSCCommentPage

Until now I have not made to find out whats the problem here - maybe some kind of a problem within one of the PostScript files?

So help would be appreciated.

EDIT:

I tested with ghostScript commandline tool:

gswin32.exe -dQUIET -dBATCH -dNOPAUSE -sDEVICE=pswrite -sOutputFile="test.ps" --filename "1.ps" "2.ps"

which results in a document where 1.ps and 2.ps are merged into one(!) page (i.e. overlay). When removing the --filename the resulting document will be a PostScript with two pages as expected.

ghost4j can't parse 2.ps, maybe there is an error in the document, I can't tell. — aalku, Nov 22 '13 at 12:02
I thought parsing happens during the call of load() and not during append? — PowerStat, Nov 22 '13 at 12:10
Btw. I have no problems with opening both PosScript files in GhostView. — PowerStat, Nov 22 '13 at 12:15

score 1 · Answer 1 · answered Nov 22 '13 at 12:45

I think something is wrong in the document or in the XMLGraphics library as it seems it cannot parse a part of it.

Here you can see the code in ghost4j that I think it is failing (link):

    DSCParser parser = new DSCParser(bais);
    Object tP = parser.nextDSCComment(DSCConstants.PAGES);
    while (tP instanceof DSCAtend)
        tP = parser.nextDSCComment(DSCConstants.PAGES);
    DSCCommentPages pages = (DSCCommentPages) tP;

And here you can see why XMLGraphics may bre sesponsable (link):

private DSCComment parseDSCComment(String name, String value) {
    DSCComment parsed = DSCCommentFactory.createDSCCommentFor(name);
    if (parsed != null) {
        try {
            parsed.parseValue(value);
            return parsed;
        } catch (Exception e) {
            //ignore and fall back to unparsed DSC comment
        }
    }
    UnparsedDSCComment unparsed = new UnparsedDSCComment(name);
    unparsed.parseValue(value);
    return unparsed;
}

It seems parsed.parseValue(value) has thrown an exception, it was hidden in the catch and it returned an unparsed version ghost4j didn't expect.

score 1 · Accepted Answer · answered Dec 30 '13 at 20:49

The exception occurs because one of the 2 documents does not follow the Adobe Document Structuring Convention (DSC), which is mandatory if you want to use the Document append method.

Use the SafeAppenderModifier instead. There is an example here: http://www.ghost4j.org/highlevelapisamples.html (Append a PDF document to a PostScript document)

ghost4j class cast exception during joining two PostScripts

2 Answers2