Java

MIME Content-Transfer-Encoding Header Field

See more MIME Examples

Explains the Content-Transfer-Encoding header field and how it affects how data is stored in the MIME.

Chilkat2 Java

import com.chilkatsoft.chilkat2.Mime;
import com.chilkatsoft.chilkat2.StringBuilder;

public class ChilkatExample {

    public static void main(String[] args) {
        // The Content-Transfer-Encoding header field is typically set to one of these values:
        //
        //   base64
        //   quoted-printable
        //   binary
        //   8bit
        //   7bit

        // If the encoding is base64 or quoted-printable, then the bytes of the content are encoded as such.
        // The values "8bit", "7bit", and "binary" all imply that NO encoding has been performed.

        // Here are some guidelines and hints:
        //
        // 1) "8bit", "7bit", and "binary" encodings (i.e. NO encoding) results in the smallest MIME.

        // 2) A "binary" encoding implies non-text data.  Binary MIME CANNOT be retrieved as a string.  It can only be retrieved as a byte array.

        // 3) "8bit" and "7bit" encodings imply text.
        //    7bit implies that the text is us-ascii (all byte values less than or equal to 0x7F).
        //    8bit implies that the text contains non-us-ascii chars.

        // 4) Base64 is the best choice for encoding non-text data, such as PDF's, images, etc.

        // 5) quoted-printable is the best choice for encoding text data where most chars are going to be us-ascii. This would typically
        //    include all Western European languages.  For Asian, Arabic, Hebrew, etc. where most chars in the text are non-us-ascii,
        //    the most efficient encoding would be base64.

        // Let's demonstrate with this small JPG image.

        StringBuilder sbJpgBase64 = new StringBuilder();
        sbJpgBase64.append("/9j/4AAQSkZJRgABAQEASABIAAD//gAmRmlsZSB3cml0dGVuIGJ5IEFkb2JlIFBob3Rvc2hvcD8g\r\n");
        sbJpgBase64.append("NC4w/9sAQwAQCwwODAoQDg0OEhEQExgoGhgWFhgxIyUdKDozPTw5Mzg3QEhcTkBEV0U3OFBtUVdf\r\n");
        sbJpgBase64.append("YmdoZz5NcXlwZHhcZWdj/9sAQwEREhIYFRgvGhovY0I4QmNjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj\r\n");
        sbJpgBase64.append("Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj/8IAEQgAFAAUAwERAAIRAQMRAf/EABcAAAMBAAAA\r\n");
        sbJpgBase64.append("AAAAAAAAAAAAAAIDBAX/xAAYAQADAQEAAAAAAAAAAAAAAAABAgMEAP/aAAwDAQACEAMQAAAB2kZY\r\n");
        sbJpgBase64.append("NNEijWKddfTmLgALWH//xAAbEAACAgMBAAAAAAAAAAAAAAABAgMRAAQSE//aAAgBAQABBQL0XqN+\r\n");
        sbJpgBase64.append("pM2aqJGMiqFFCyg7z//EABwRAAICAgMAAAAAAAAAAAAAAAERAAIQIQMSUf/aAAgBAwEBPwHqU5aq\r\n");
        sbJpgBase64.append("Axx+y1tMQl4elj//xAAcEQEAAQUBAQAAAAAAAAAAAAABEQACEBIhA1H/2gAIAQIBAT8B3Bhqy7Zc\r\n");
        sbJpgBase64.append("enyiwmGgDhiOzj//xAAdEAABAwUBAAAAAAAAAAAAAAABAAIREBIhIkFR/9oACAEBAAY/ArZyn+Cg\r\n");
        sbJpgBase64.append("xtxWuJaoCnqDuin/xAAcEAABBAMBAAAAAAAAAAAAAAABABEhYRAxQVH/2gAIAQEAAT8hkEwPUUR9\r\n");
        sbJpgBase64.append("DYfE4nxtRpIkBTsayuALIiuY/9oADAMBAAIAAwAAABDWPTsf/8QAGhEAAwADAQAAAAAAAAAAAAAA\r\n");
        sbJpgBase64.append("AAEREDFBIf/aAAgBAwEBPxC0DVPcWm+Ce4OesrkE6bjH/8QAGBEBAQEBAQAAAAAAAAAAAAAAAREA\r\n");
        sbJpgBase64.append("QRD/2gAIAQIBAT8QahMiOc8YgSrnTY3ELclHXn//xAAcEAEBAAIDAQEAAAAAAAAAAAABEQAhMUFx\r\n");
        sbJpgBase64.append("EFH/2gAIAQEAAT8Qn3igmSZSj+c4N4zapMy9IjFV98wncN2iuLFsCEbDGxQkI6RO/n//2Q==\r\n");

        Mime mime = new Mime();
        mime.setContentType("image/jpeg");
        mime.setBodyFromEncoded("base64", sbJpgBase64.getAsString());

        System.out.println(mime.getMime());
        System.out.println("-");

        // The result:
        //
        //     Content-Type: image/jpeg
        //     Content-Transfer-Encoding: base64
        //
        //     /9j/4AAQSkZJRgABAQEASABIAAD//gAmRmlsZSB3cml0dGVuIGJ5IEFkb2JlIFBob3Rvc2hvcD8g
        //     NC4w/9sAQwAQCwwODAoQDg0OEhEQExgoGhgWFhgxIyUdKDozPTw5Mzg3QEhcTkBEV0U3OFBtUVdf
        //     YmdoZz5NcXlwZHhcZWdj/9sAQwEREhIYFRgvGhovY0I4QmNjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj
        //     Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj/8IAEQgAFAAUAwERAAIRAQMRAf/EABcAAAMBAAAA
        //     AAAAAAAAAAAAAAIDBAX/xAAYAQADAQEAAAAAAAAAAAAAAAABAgMEAP/aAAwDAQACEAMQAAAB2kZY
        //     NNEijWKddfTmLgALWH//xAAbEAACAgMBAAAAAAAAAAAAAAABAgMRAAQSE//aAAgBAQABBQL0XqN+
        //     pM2aqJGMiqFFCyg7z//EABwRAAICAgMAAAAAAAAAAAAAAAERAAIQIQMSUf/aAAgBAwEBPwHqU5aq
        //     Axx+y1tMQl4elj//xAAcEQEAAQUBAQAAAAAAAAAAAAABEQACEBIhA1H/2gAIAQIBAT8B3Bhqy7Zc
        //     enyiwmGgDhiOzj//xAAdEAABAwUBAAAAAAAAAAAAAAABAAIREBIhIkFR/9oACAEBAAY/ArZyn+Cg
        //     xtxWuJaoCnqDuin/xAAcEAABBAMBAAAAAAAAAAAAAAABABEhYRAxQVH/2gAIAQEAAT8hkEwPUUR9
        //     DYfE4nxtRpIkBTsayuALIiuY/9oADAMBAAIAAwAAABDWPTsf/8QAGhEAAwADAQAAAAAAAAAAAAAA
        //     AAEREDFBIf/aAAgBAwEBPxC0DVPcWm+Ce4OesrkE6bjH/8QAGBEBAQEBAQAAAAAAAAAAAAAAAREA
        //     QRD/2gAIAQIBAT8QahMiOc8YgSrnTY3ELclHXn//xAAcEAEBAAIDAQEAAAAAAAAAAAABEQAhMUFx
        //     EFH/2gAIAQEAAT8Qn3igmSZSj+c4N4zapMy9IjFV98wncN2iuLFsCEbDGxQkI6RO/n//2Q==
        //

        // Set the Content-Transfer-Encoding to "binary" by setting the Encoding property.
        mime.setEncoding("binary");

        // Try to get the MIME string.  This CANNOT be done.  The bytes of the JPG image do not
        // represent chars, and to return a string means that bytes must be interpreted according
        // to some character encoding (such as utf-8).  Non-text binary bytes can only be
        // contained in a string IF encoded in some way. Encodings such as Base64, quoted-printable,
        // URL, etc. exist to make it possible to represent binary data in string format.
        System.out.println(mime.getMime());
        System.out.println("-");

        // We CAN get the binary MIME as bytes..

ERROR: Invalid type for Chilkat2 Java: pbytes
ERROR: Method not in Chilkat2 Java: Mime.GetMimeBytes
        mimeBytes = mime.ERROR();

        // Regardless of the Content-Transfer-Encoding, the
        // body content can always be retrieved and the body bytes
        // decoded from whatever encoding is used..

ERROR: Invalid type for Chilkat2 Java: pbytes
ERROR: Method not in Chilkat2 Java: Mime.GetBodyBinary
        jpgBytes = mime.ERROR();

        // To get the body in base64 format, first make sure
        // the Content-Transfer-Encoding is base64, then call GetBodyEncoded.
        mime.setEncoding("base64");
        String jpgBase64 = mime.getBodyEncoded();
        System.out.println(jpgBase64);
        System.out.println("-");

        // Let's go back to "binary" MIME..
        mime.setEncoding("binary");

        // Let's say we have MIME, and it was loaded directly from a file, or from
        // a byte array.  (It was not loaded from the contents of a string variable.)
        // We don't know whether the MIME contains binary or 8bit encodings, and thus
        // we dont' know if the MIME is safe to get as a string.
        // The Convert8Bit method can be called to recursively traverse the MIME and set
        // all 8bit or binary encodings to "base64".  This makes the MIME safe for storing in
        // a string.
        mime.convert8Bit();
        String mimeStr = mime.getMime();
        System.out.println(mimeStr);
        System.out.println("-");
    }
}