Receiving Emails with the Google App Engine

Last year, in November, I did explore for the first time the Google App Engine for Java (GAE/J). One of the feature my application provides is to accept an email and translate it to an RSS 2.0 item.
The first version of the receiver was done using JavaMail. I did experiment some troubles with the "Quoted-Transfer-Encoding", sometimes the content was broken.
Using the current version of the GAE/J (1.3.0) the emails content received from Gmail or from Thunderbird is correct and the channel seems to be reliable.

Mime4J

An alternative for receiving email is the James Mime4J project.
The library doesn't have dependencies and works on the GAE/J. It is quite simple to use; instead of:

import java.io.InputStream;
import java.util.Properties;
import javax.mail.Session;
import javax.mail.internet.MimeMessage;
...
InputStream input = request.getInputStream(); // ServletRequest
Properties props = new Properties();
Session session = Session.getDefaultInstance(props, null);
MimeMessage message = new MimeMessage(session, input); // MessagingException
...
  

you have to use:

import java.io.InputStream;
import org.apache.james.mime4j.message.Message;
import org.apache.james.mime4j.message.MessageBuilder;
import org.apache.james.mime4j.parser.ContentHandler;
import org.apache.james.mime4j.parser.MimeStreamParser;
import org.apache.james.mime4j.storage.MemoryStorageProvider;
...
InputStream input = request.getInputStream(); // ServletRequest
Message message = new Message();
ContentHandler handler = new MessageBuilder(message, new MemoryStorageProvider());
MimeStreamParser parser = new MimeStreamParser();
parser.setContentHandler(handler);
parser.parse(input); // MimeException
...

The result seems to be better than the one which uses JavaMail. The mails received from the MS Outlook are readable. It remains a small problem with the encoding which I will investigate later this year.

Incoming Mail Syntax

The syntax of the incoming mail was changed:

description
line 1
line 2
...
line n
end

link
http://myserver/mylink
end

categories
category 1
category 2
...
category n
end

Each command block starts with a keyword and ends with end

Informations

The email address of the Mime4J service is mime4j@example-rest.appspotmail.com, the JavaMail based receiver still works with rss2@example-rest.appspotmail.com
The application URL is example-rest.appspot.com.