pdfbox-trunk/preflight/src/main/java/org/apache/pdfbox/preflight/process/PageTreeValidationProcess.java
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package org.apache.pdfbox.preflight.process;

import org.apache.pdfbox.cos.COSDictionary;
import org.apache.pdfbox.cos.COSName;
import static org.apache.pdfbox.preflight.PreflightConfiguration.PAGE_PROCESS;
import static org.apache.pdfbox.preflight.PreflightConstants.ERROR_SYNTAX_NOCATALOG;

import org.apache.pdfbox.pdmodel.PDDocumentCatalog;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.preflight.PreflightConstants;
import static org.apache.pdfbox.preflight.PreflightConstants.ERROR_PDF_PROCESSING_MISSING;
import org.apache.pdfbox.preflight.PreflightContext;
import org.apache.pdfbox.preflight.ValidationResult.ValidationError;
import org.apache.pdfbox.preflight.exception.ValidationException;
import org.apache.pdfbox.preflight.utils.ContextHelper;

public class PageTreeValidationProcess extends AbstractProcess
{

    @Override
    public void validate(PreflightContext context) throws ValidationException
    {
        PDDocumentCatalog catalog = context.getDocument().getDocumentCatalog();
        if (catalog != null)
        {
            COSDictionary catalogDict = catalog.getCOSObject();
            if (!(catalogDict.getDictionaryObject(COSName.PAGES) instanceof COSDictionary))
            {
                addValidationError(context, new ValidationError(ERROR_PDF_PROCESSING_MISSING, 
                        "/Pages dictionary entry is missing in document catalog"));
                return;
            }
            int p = 0;
            for (PDPage page : context.getDocument().getPages())
            {
                context.setCurrentPageNumber(p);
                validatePage(context, page);

                if (context.getDocument().getValidationErrors().size() > context.getConfig()
                        .getMaxErrors())
                {
                    context.addValidationError(new ValidationError(PreflightConstants.ERROR_UNKNOWN_ERROR, 
                            "Over " + context.getConfig().getMaxErrors() +
                            " errors, page tree validation process aborted"));
                    break;
                }
                context.setCurrentPageNumber(null);
                ++p;
            }
        }
        else
        {
            context.addValidationError(new ValidationError(ERROR_SYNTAX_NOCATALOG, "There are no Catalog entry in the Document"));
        }
    }

    private void validatePage(PreflightContext context, PDPage page) throws ValidationException
    {
        ContextHelper.validateElement(context, page, PAGE_PROCESS);
    }
}
