问如何从不可搜索的pdf中检测出可搜索的pdf？

EN

public static boolean isSearchablePdf(String filePath) throws Exception {

    String parsedText;
    PDFTextStripper pdfStripper = null;
    PDDocument document = null;
    COSDocument cosDoc = null;
    File file = new File(filePath);
    boolean isSearchable = true;

    PDFParser parser = new PDFParser(new RandomAccessFile(file, "r"));
    parser.parse();
    cosDoc = parser.getDocument();
    pdfStripper = new PDFTextStripper();
    document = new PDDocument(cosDoc);
    int noOfPages = document.getNumberOfPages();

    for (int page = 1; page <= noOfPages; page++) {

        pdfStripper.setStartPage(page);
        pdfStripper.setEndPage(page);

        parsedText = pdfStripper.getText(document);
        isSearchable = isSearchable & isSearchablePDFContent(parsedText, page);

        if (!isSearchable) {
            break;
        }
        if (page >= 5) {
            break;
        }

    }
    if (isSearchable && noOfPages > 10) {
        int min = 5;
        int max = noOfPages;
        for (int i = 0; i < 4; i++) {
            int randomNo = min + (int) (Math.random() * ((max - min) + 1));
            pdfStripper.setStartPage(randomNo);
            pdfStripper.setEndPage(randomNo);
            parsedText = pdfStripper.getText(document);
            isSearchable = isSearchable & isSearchablePDFContent(parsedText, randomNo);
            if (!isSearchable)
                break;
        }
    }
    if (isSearchable && noOfPages >= 10) {
        for (int page = noOfPages - 5; page < noOfPages; page++) {
            pdfStripper.setStartPage(page);
            pdfStripper.setEndPage(page);
            parsedText = pdfStripper.getText(document);
            isSearchable = isSearchable & isSearchablePDFContent(parsedText, page);
            if (!isSearchable)
                break;

        }
    }

    if (document != null){
        document.close();
    }

    return isSearchable;
}

public static boolean isSearchablePDFContent(String contentOfPdf, int pageNo) throws IOException {
    int count = 0;
    boolean isSearchable = false;
    if (!contentOfPdf.isEmpty()) {
        StringTokenizer st = new StringTokenizer(contentOfPdf);
        while (st.hasMoreTokens()) {
            st.nextToken();
            if (count >= 3) {
                isSearchable = true;
                break;
            }
            count++;
        }

    } else {
        isSearchable = false;
    }

    return isSearchable;
}