The Java sample code is available for browsing in the repository, and can also be downloaded in a ZIP file.

You'll need the following packages installed on your system to run the sample code:

• JDK version 1.5 or higher
• The JavaMail API version 1.4.5 or higher. This is available alone or as part of Java EE.
• Apache Ant
• An OAuth Token and Token Secret for a Gmail account. You can use oauth2.py to generate these for your own account.

Download the sample code package from here, unzip it, and change into the oauth2-java-sample-20120904 directory.

Open the file build.properties in a text editor and modify the following properties:

• javamail_jar: If you are not using a Java EE jdk and need to specifically include the location of the JavaMail JAR file, put that here. Otherwise it's ok to leave this property blank.
• email: The email address of a Gmail account to which you want to authenticate.
• oauthToken: A valid OAuth2 access token for the Gmail account.

Save build.properties and close your editor

Execute ant run to run the sample application with the parameters you specified in build.properties. If everything worked properly, you should see some debug output including the lines:

[...]
[java] Successfully authenticated to IMAP.
[...]
[java] Successfully authenticated to SMTP.

The high-level sample code is in OAuth2Authenticator.java. The two important methods are initialize and connectToImap. initialize installs a SaslClient provider of the XOAUTH2 mechanism; it needs to be called once before any calls to connectToImap. connectToImap can be called to open new IMAP connections and authenticate to them with XOAUTH2.