Java

Add a Custom Header to a Related Item

Demonstrates the Chilkat Email.AddRelatedHeader method, which adds a custom MIME header field to an existing related item identified by its zero-based index. This example first adds a related style sheet (which becomes index 0) and captures its generated Content-ID, builds an HTML body that references the style sheet by that cid:, then attaches an extra header field to the related item and prints the resulting MIME.

Background: Like attachments, each related item (an inline image, style sheet, etc.) is a MIME part with its own small header block describing that part — Content-Type, Content-ID, Content-Location, and so on. AddRelatedHeader lets you insert additional fields into that per-part block, which is occasionally required for interoperability with clients that look for specific custom headers on embedded resources.

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import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Email;
import com.chilkatsoft.chilkat2.StringBuilder;

public class ChilkatExample {

    public static void main(String[] args) {
        // Demonstrates the AddRelatedHeader method, which adds a custom MIME header field to an
        // existing related item, identified by its zero-based index.

        Email email = new Email();
        email.setSubject("Related item with a custom header");

        // Add a related item first (a style sheet); capture its generated Content-ID.  It becomes
        // related-item index 0.
        String cid;
        try {
            cid = email.addRelatedString("styles.css", "body { color: black; }", "utf-8");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Build the HTML body, referencing the related style sheet by its Content-ID.  A
        // placeholder is used and then replaced with the actual Content-ID.
        StringBuilder sbHtml = new StringBuilder();
        sbHtml.append("<html><head><link rel=\"stylesheet\" href=\"cid:PLACEHOLDER_CID\"/></head><body>Styled content.</body></html>");
        int numReplaced = sbHtml.replace("PLACEHOLDER_CID", cid);
        email.setHtmlBody(sbHtml.getAsString());

        // Add a custom header field to the first related item (index 0).
        email.addRelatedHeader(0, "X-Custom-Related-Header", "some value");

        // The custom header now appears in the related item's MIME part.
        System.out.println(email.getMime());
    }
}