Mail multipart/alternative vs multipart/mixed
When creating email messages you are supposed to set the Content-Type to multipart/alternative when sending HTML and TEXT or multipart/mixed when sending TEXT and attachments.
So what do you do if you want to send HTML, Text, and attachments? Use both?
Answer
I hit this challenge today and I found these answers useful but not quite explicit enough for me.
Edit: Just found the Apache Commons Email that wraps this up nicely, meaning you don't need to know below.
If your requirement is an email with:
- text and html versions
- html version has embedded (inline) images
- attachments
The only structure I found that works with Gmail/Outlook/iPad is:
- mixed
- alternative
- text
- related
- html
- inline image
- inline image
- attachment
- attachment
- alternative
And the code is:
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.URLDataSource;
import javax.mail.BodyPart;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMultipart;
import java.net.URL;
import java.util.HashMap;
import java.util.List;
import java.util.UUID;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* Created by StrongMan on 25/05/14.
*/
public class MailContentBuilder {
private static final Pattern COMPILED_PATTERN_SRC_URL_SINGLE = Pattern.compile("src='([^']*)'", Pattern.CASE_INSENSITIVE);
private static final Pattern COMPILED_PATTERN_SRC_URL_DOUBLE = Pattern.compile("src=\"([^\"]*)\"", Pattern.CASE_INSENSITIVE);
/**
* Build an email message.
*
* The HTML may reference the embedded image (messageHtmlInline) using the filename. Any path portion is ignored to make my life easier
* e.g. If you pass in the image C:\Temp\dog.jpg you can use <img src="dog.jpg"/> or <img src="C:\Temp\dog.jpg"/> and both will work
*
* @param messageText
* @param messageHtml
* @param messageHtmlInline
* @param attachments
* @return
* @throws MessagingException
*/
public Multipart build(String messageText, String messageHtml, List<URL> messageHtmlInline, List<URL> attachments) throws MessagingException {
final Multipart mpMixed = new MimeMultipart("mixed");
{
// alternative
final Multipart mpMixedAlternative = newChild(mpMixed, "alternative");
{
// Note: MUST RENDER HTML LAST otherwise iPad mail client only renders the last image and no email
addTextVersion(mpMixedAlternative,messageText);
addHtmlVersion(mpMixedAlternative,messageHtml, messageHtmlInline);
}
// attachments
addAttachments(mpMixed,attachments);
}
//msg.setText(message, "utf-8");
//msg.setContent(message,"text/html; charset=utf-8");
return mpMixed;
}
private Multipart newChild(Multipart parent, String alternative) throws MessagingException {
MimeMultipart child = new MimeMultipart(alternative);
final MimeBodyPart mbp = new MimeBodyPart();
parent.addBodyPart(mbp);
mbp.setContent(child);
return child;
}
private void addTextVersion(Multipart mpRelatedAlternative, String messageText) throws MessagingException {
final MimeBodyPart textPart = new MimeBodyPart();
textPart.setContent(messageText, "text/plain");
mpRelatedAlternative.addBodyPart(textPart);
}
private void addHtmlVersion(Multipart parent, String messageHtml, List<URL> embeded) throws MessagingException {
// HTML version
final Multipart mpRelated = newChild(parent,"related");
// Html
final MimeBodyPart htmlPart = new MimeBodyPart();
HashMap<String,String> cids = new HashMap<String, String>();
htmlPart.setContent(replaceUrlWithCids(messageHtml,cids), "text/html");
mpRelated.addBodyPart(htmlPart);
// Inline images
addImagesInline(mpRelated, embeded, cids);
}
private void addImagesInline(Multipart parent, List<URL> embeded, HashMap<String,String> cids) throws MessagingException {
if (embeded != null)
{
for (URL img : embeded)
{
final MimeBodyPart htmlPartImg = new MimeBodyPart();
DataSource htmlPartImgDs = new URLDataSource(img);
htmlPartImg.setDataHandler(new DataHandler(htmlPartImgDs));
String fileName = img.getFile();
fileName = getFileName(fileName);
String newFileName = cids.get(fileName);
boolean imageNotReferencedInHtml = newFileName == null;
if (imageNotReferencedInHtml) continue;
// Gmail requires the cid have <> around it
htmlPartImg.setHeader("Content-ID", "<"+newFileName+">");
htmlPartImg.setDisposition(BodyPart.INLINE);
parent.addBodyPart(htmlPartImg);
}
}
}
private void addAttachments(Multipart parent, List<URL> attachments) throws MessagingException {
if (attachments != null)
{
for (URL attachment : attachments)
{
final MimeBodyPart mbpAttachment = new MimeBodyPart();
DataSource htmlPartImgDs = new URLDataSource(attachment);
mbpAttachment.setDataHandler(new DataHandler(htmlPartImgDs));
String fileName = attachment.getFile();
fileName = getFileName(fileName);
mbpAttachment.setDisposition(BodyPart.ATTACHMENT);
mbpAttachment.setFileName(fileName);
parent.addBodyPart(mbpAttachment);
}
}
}
public String replaceUrlWithCids(String html, HashMap<String,String> cids)
{
html = replaceUrlWithCids(html, COMPILED_PATTERN_SRC_URL_SINGLE, "src='cid:@cid'", cids);
html = replaceUrlWithCids(html, COMPILED_PATTERN_SRC_URL_DOUBLE, "src=\"cid:@cid\"", cids);
return html;
}
private String replaceUrlWithCids(String html, Pattern pattern, String replacement, HashMap<String,String> cids) {
Matcher matcherCssUrl = pattern.matcher(html);
StringBuffer sb = new StringBuffer();
while (matcherCssUrl.find())
{
String fileName = matcherCssUrl.group(1);
// Disregarding file path, so don't clash your filenames!
fileName = getFileName(fileName);
// A cid must start with @ and be globally unique
String cid = "@" + UUID.randomUUID().toString() + "_" + fileName;
if (cids.containsKey(fileName))
cid = cids.get(fileName);
else
cids.put(fileName,cid);
matcherCssUrl.appendReplacement(sb,replacement.replace("@cid",cid));
}
matcherCssUrl.appendTail(sb);
html = sb.toString();
return html;
}
private String getFileName(String fileName) {
if (fileName.contains("/"))
fileName = fileName.substring(fileName.lastIndexOf("/")+1);
return fileName;
}
}
And an example of using it with from Gmail
/**
* Created by StrongMan on 25/05/14.
*/
import com.sun.mail.smtp.SMTPTransport;
import java.net.URL;
import java.security.Security;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.URLDataSource;
import javax.mail.*;
import javax.mail.internet.*;
/**
*
* http://stackoverflow.com/questions/14744197/best-practices-sending-javamail-mime-multipart-emails-and-gmail
* http://stackoverflow.com/questions/3902455/smtp-multipart-alternative-vs-multipart-mixed
*
*
*
* @author doraemon
*/
public class GoogleMail {
private GoogleMail() {
}
/**
* Send email using GMail SMTP server.
*
* @param username GMail username
* @param password GMail password
* @param recipientEmail TO recipient
* @param title title of the message
* @param messageText message to be sent
* @throws AddressException if the email address parse failed
* @throws MessagingException if the connection is dead or not in the connected state or if the message is not a MimeMessage
*/
public static void Send(final String username, final String password, String recipientEmail, String title, String messageText, String messageHtml, List<URL> messageHtmlInline, List<URL> attachments) throws AddressException, MessagingException {
GoogleMail.Send(username, password, recipientEmail, "", title, messageText, messageHtml, messageHtmlInline,attachments);
}
/**
* Send email using GMail SMTP server.
*
* @param username GMail username
* @param password GMail password
* @param recipientEmail TO recipient
* @param ccEmail CC recipient. Can be empty if there is no CC recipient
* @param title title of the message
* @param messageText message to be sent
* @throws AddressException if the email address parse failed
* @throws MessagingException if the connection is dead or not in the connected state or if the message is not a MimeMessage
*/
public static void Send(final String username, final String password, String recipientEmail, String ccEmail, String title, String messageText, String messageHtml, List<URL> messageHtmlInline, List<URL> attachments) throws AddressException, MessagingException {
Security.addProvider(new com.sun.net.ssl.internal.ssl.Provider());
final String SSL_FACTORY = "javax.net.ssl.SSLSocketFactory";
// Get a Properties object
Properties props = System.getProperties();
props.setProperty("mail.smtps.host", "smtp.gmail.com");
props.setProperty("mail.smtp.socketFactory.class", SSL_FACTORY);
props.setProperty("mail.smtp.socketFactory.fallback", "false");
props.setProperty("mail.smtp.port", "465");
props.setProperty("mail.smtp.socketFactory.port", "465");
props.setProperty("mail.smtps.auth", "true");
/*
If set to false, the QUIT command is sent and the connection is immediately closed. If set
to true (the default), causes the transport to wait for the response to the QUIT command.
ref : http://java.sun.com/products/javamail/javadocs/com/sun/mail/smtp/package-summary.html
http://forum.java.sun.com/thread.jspa?threadID=5205249
smtpsend.java - demo program from javamail
*/
props.put("mail.smtps.quitwait", "false");
Session session = Session.getInstance(props, null);
// -- Create a new message --
final MimeMessage msg = new MimeMessage(session);
// -- Set the FROM and TO fields --
msg.setFrom(new InternetAddress(username + "@gmail.com"));
msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipientEmail, false));
if (ccEmail.length() > 0) {
msg.setRecipients(Message.RecipientType.CC, InternetAddress.parse(ccEmail, false));
}
msg.setSubject(title);
// mixed
MailContentBuilder mailContentBuilder = new MailContentBuilder();
final Multipart mpMixed = mailContentBuilder.build(messageText, messageHtml, messageHtmlInline, attachments);
msg.setContent(mpMixed);
msg.setSentDate(new Date());
SMTPTransport t = (SMTPTransport)session.getTransport("smtps");
t.connect("smtp.gmail.com", username, password);
t.sendMessage(msg, msg.getAllRecipients());
t.close();
}
}