Mock Javamail primer

Small primer for mock javamail, a pretty useful project that will be handy whenever you need to test code that uses POP3/IMAP/SMTP and you wouldn't like to build wrappers for anything you need to test - javamail does not really offer interfaces that can be implemented by mock objects, but different implementations can be used at runtime depending on which jars are on the classpath.

Take a look at the project homepage:

http://java.net/projects/mock-javamail

Be sure you've enabled java.net Maven repo, and add this dependency to your pom.xml:

1         <dependency>


2             <groupId>org.jvnet.mock-javamail</groupId>


3             <artifactId>mock-javamail</artifactId>


4             <version>1.9</version>


5             <scope>test</scope>


6         </dependency>

You're almost ready; now setup your test code this way:

 1 public class IMAPMailRepositoryTest {


 2     @Before


 3     public void setUp() throws Exception {


 4         final Session session = Session.getInstance(


 5                 System.getProperties());


 6


 7         MimeMessage msg = new MimeMessage(


 8                 session);


 9         msg.setRecipients(Message.RecipientType.TO,


10                 "testuser@mockserver.com");


11         msg.setSubject("Some Subject");


12         msg.setText("sometext");


13         Transport.send(msg);


14     }


15


16     @After


17     public void tearDown() throws Exception {


18         Mailbox.clearAll();


19     }

Now you're ready to use your mock javamail:

 1 public class SomeImapClient {


 2


 3     private static Logger log = Logger.getLogger(SomeImapClient.class);


 4


 5     public void processMail() {


 6         try {


 7             Session session = getMailSession();


 8             Store store = connect(session);


 9             Folder folder = openMailFolder(store);


10             findContent(folder);


11         } catch (MessagingException e) {


12             throw new RuntimeException(e);


13         } catch (IOException e) {


14             throw new RuntimeException(e);


15         }


16


17     }


18


19     public Session getMailSession() {


20         Properties props = System.getProperties();


21         props.setProperty("mail.store.protocol", "imaps");


22         props.setProperty("mail.imap.partialfetch", "0");


23


24         log.debug("Getting session");


25         return Session.getDefaultInstance(props, null);


26


27     }


28


29     public Store connect(Session session) throws MessagingException {


30         log.debug("getting the session for accessing email.");


31         Store store = session.getStore("imap");


32


33         store.connect("mockserver.com", "testuser", "somepassword");


34         log.debug("Connection established with IMAP server.");


35         return store;


36     }


37


38     public Folder openMailFolder(Store store) throws MessagingException {


39         Folder folder = store.getDefaultFolder();


40         folder = folder.getFolder("inbox");


41         folder.open(Folder.READ_ONLY);


42         return folder;


43     }


44


45     public void findContent(Folder folder) throws MessagingException, IOException {


46         for (Message m : folder.getMessages()) {


47             log.debug(m.getSubject());


48


49         }


50


51


52     }


53


54


55 }

Output is:

DEBUG 30 Aug 2011 19:25:25 SomeImapClient:32 - Getting session

DEBUG 30 Aug 2011 19:25:25 SomeImapClient:38 - getting the session for accessing email.

DEBUG 30 Aug 2011 19:25:25 SomeImapClient:42 - Connection established with IMAP server.

DEBUG 30 Aug 2011 19:25:25 SomeImapClient:55 - Some Subject

Some small gotchas:

• your store.connect("example.com", "username", "anything") must match your "username@example.com" addressee in msg.setRecipients; different addressees will yield multiple mailboxes.
• Only works for plain imap & pop3 mailboxes. Even though it doesn't make a lot of sense to use SSL on a mock mailbox, if you try getting the "imaps" store you'll get an error as a real implementation of javamail will be employed.
• I'd always advise to use such tearDown() when doing unit tests, since the Session seems global and different tests could interfere with different contents - unless you use a different fake user/test server url in each of your tests.