How to encode Chinese text in QR barcodes generated with iTextSharp?

问题

I'm trying to draw QR barcodes in a PDF file using iTextSharp. If I'm using English text the barcodes are fine, they are decoded properly, but if I'm using Chinese text, the barcode is decoded as question marks. For example this character '测' (\u6D4B) is decoded as '?'. I tried all supported character sets, but none of them helped.
What combination of parameters should I use for the QR barcode in iTextSharp in order to encode correctly Chinese text?

回答1:

iText and iTextSharp apparently don't natively support this but you can write some code to handle this on your own. The trick is to get the QR code parser to work with just an arbitrary byte array instead of a string. What's really nice is that the iTextSharp code is almost ready for this but doesn't expose the functionality. Unfortunately many of the required classes are sealed so you can't just subclass them, you'll have to recreate them. You can either download the entire source and add these changes or just create separate classes with the same names. (Please check over the license to make sure you are allowed to do this.) My changes below don't have any error correction so make sure you do that, too.

The first class that you'll need to recreate is iTextSharp.text.pdf.qrcode.BlockPair and the only change you'll need to make is to make the constructor public instead of internal. (You only need to do this if you are creating your own code and not modifying the existing code.)

The second class is iTextSharp.text.pdf.qrcode.Encoder. This is where we'll make the most changes. Add an overload to Append8BitBytes that looks like this:

static void Append8BitBytes(byte[] bytes, BitVector bits) {
    for (int i = 0; i < bytes.Length; ++i) {
        bits.AppendBits(bytes[i], 8);
    }
}

The string version of this method converts text to a byte array and then uses the above so we're just cutting out the middle man. Next, add a new overload to the constructor that takes in a byte array instead of a string. We'll then just cut out the string detection part and force the system to byte-mode, otherwise the code below is pretty much the same.

    public static void Encode(byte[] bytes, ErrorCorrectionLevel ecLevel, IDictionary<EncodeHintType, Object> hints, QRCode qrCode) {
        String encoding = DEFAULT_BYTE_MODE_ENCODING;

        // Step 1: Choose the mode (encoding).
        Mode mode = Mode.BYTE;

        // Step 2: Append "bytes" into "dataBits" in appropriate encoding.
        BitVector dataBits = new BitVector();
        Append8BitBytes(bytes, dataBits);

        // Step 3: Initialize QR code that can contain "dataBits".
        int numInputBytes = dataBits.SizeInBytes();
        InitQRCode(numInputBytes, ecLevel, mode, qrCode);

        // Step 4: Build another bit vector that contains header and data.
        BitVector headerAndDataBits = new BitVector();

        // Step 4.5: Append ECI message if applicable
        if (mode == Mode.BYTE && !DEFAULT_BYTE_MODE_ENCODING.Equals(encoding)) {
            CharacterSetECI eci = CharacterSetECI.GetCharacterSetECIByName(encoding);
            if (eci != null) {
                AppendECI(eci, headerAndDataBits);
            }
        }

        AppendModeInfo(mode, headerAndDataBits);

        int numLetters = dataBits.SizeInBytes();
        AppendLengthInfo(numLetters, qrCode.GetVersion(), mode, headerAndDataBits);
        headerAndDataBits.AppendBitVector(dataBits);

        // Step 5: Terminate the bits properly.
        TerminateBits(qrCode.GetNumDataBytes(), headerAndDataBits);

        // Step 6: Interleave data bits with error correction code.
        BitVector finalBits = new BitVector();
        InterleaveWithECBytes(headerAndDataBits, qrCode.GetNumTotalBytes(), qrCode.GetNumDataBytes(),
            qrCode.GetNumRSBlocks(), finalBits);

        // Step 7: Choose the mask pattern and set to "qrCode".
        ByteMatrix matrix = new ByteMatrix(qrCode.GetMatrixWidth(), qrCode.GetMatrixWidth());
        qrCode.SetMaskPattern(ChooseMaskPattern(finalBits, qrCode.GetECLevel(), qrCode.GetVersion(),
            matrix));

        // Step 8.  Build the matrix and set it to "qrCode".
        MatrixUtil.BuildMatrix(finalBits, qrCode.GetECLevel(), qrCode.GetVersion(),
            qrCode.GetMaskPattern(), matrix);
        qrCode.SetMatrix(matrix);
        // Step 9.  Make sure we have a valid QR Code.
        if (!qrCode.IsValid()) {
            throw new WriterException("Invalid QR code: " + qrCode.ToString());
        }
    }

The third class is iTextSharp.text.pdf.qrcode.QRCodeWriter and once again we just need to add an overloaded Encode method supports a byte array and that calls are new constructor created above:

    public ByteMatrix Encode(byte[] bytes, int width, int height, IDictionary<EncodeHintType, Object> hints) {
        ErrorCorrectionLevel errorCorrectionLevel = ErrorCorrectionLevel.L;
        if (hints != null && hints.ContainsKey(EncodeHintType.ERROR_CORRECTION))
            errorCorrectionLevel = (ErrorCorrectionLevel)hints[EncodeHintType.ERROR_CORRECTION];

        QRCode code = new QRCode();
        Encoder.Encode(bytes, errorCorrectionLevel, hints, code);
        return RenderResult(code, width, height);
    }

The last class is iTextSharp.text.pdf.BarcodeQRCode which we once again add our new constructor overload:

    public BarcodeQRCode(byte[] bytes, int width, int height, IDictionary<EncodeHintType, Object> hints) {
        newCode.QRCodeWriter qc = new newCode.QRCodeWriter();
        bm = qc.Encode(bytes, width, height, hints);
    }

The last trick is to make sure when calling this that you include the byte order mark (BOM) so that decoders know to decode this properly, in this case UTF-8.

//Create an encoder that supports outputting a BOM
System.Text.Encoding enc = new System.Text.UTF8Encoding(true, true);

//Get the BOM
byte[] bom = enc.GetPreamble();

//Get the raw bytes for the string
byte[] bytes = enc.GetBytes("测");

//Combine the byte arrays
byte[] final = new byte[bom.Length + bytes.Length];
System.Buffer.BlockCopy(bom, 0, final, 0, bom.Length);
System.Buffer.BlockCopy(bytes, 0, final, bom.Length, bytes.Length);

//Create are barcode using our new constructor
var q = new BarcodeQRCode(final, 100, 100, null);

//Add it to the document
doc.Add(q.GetImage());

回答2:

Looks like you may be out of luck. I tried too and got the same results as you did. Then looked at the Java API:

"*CHARACTER_SET the values are strings and can be Cp437, Shift_JIS and ISO-8859-1 to ISO-8859-16. The default value is ISO-8859-1.*"

Lastly, looked at the iTextSharp BarcodeQRCode class source code to confirm that only those characters sets are supported. I'm by no means an authority on Unicode or encoding, but according to ISO/IEC 8859, the character sets above won't work for Chinese.

回答3:

Essentially the same trick that Chris has done in his answer could be implemented by specifying UTF-8 charset in barcode hints.

var hints = new Dictionary<EncodeHintType, Object>() {{EncodeHintType.CHARACTER_SET, "UTF-8"}};
var q = new BarcodeQRCode("\u6D4B", 100, 100, hints);

If you want to be more safe, you can start your string with BOM character '\uFEFF', like Chris suggested, so it would be "\uFEFF\u6D4B".

UTF-8 is unfortunately not supported by QR codes specification, and there are a lot of discussions on this subject, but the fact is that most QR code readers will correctly read the code created by this method.

来源：https://stackoverflow.com/questions/9700782/how-to-encode-chinese-text-in-qr-barcodes-generated-with-itextsharp

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