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Mapping Servlets To App Engine XMPP Requests

Here’s an example of how to configure servlets to accept XMPP requests. The XML below should be added to the web.xml file in the /war/WEB-INF directory.

This XML snippet configures three servlets: ChatServlet (handles inbound XMPP chat messages), PresenceServlet (handles requests for the application’s presence information, and presence info for other clients) and SubscribeServlet (when other XMPP users grant the application access to their presence information).

<!-- Handles the chat part of XMPP. -->
<servlet>
    <servlet-name>Chat</servlet-name>
    <servlet-class>com.example.xmpp.ChatServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>Chat</servlet-name>
    <url-pattern>/_ah/xmpp/message/chat/</url-pattern>
</servlet-mapping>
<!-- Handles the presence part of XMPP. -->
<servlet>
    <servlet-name>Presence</servlet-name>
    <servlet-class>com.example.xmpp.PresenceServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>Presence</servlet-name>
    <url-pattern>/_ah/xmpp/presence/*</url-pattern>
</servlet-mapping>  
<!-- Handles the subscription part of XMPP. -->
<servlet>
    <servlet-name>Subscribe</servlet-name>
    <servlet-class>com.example.xmpp.SubscribeServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>Subscribe</servlet-name>
    <url-pattern>/_ah/xmpp/subscription/*</url-pattern>
</servlet-mapping>
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Sending A XMPP Message

Here’s a code sample demonstrating how to send a XMPP message using the App Engine XMPP service. The text of the message is contained in the string reply_body while the recipient is represented by a JID object named from_jid . Applications can retrieve the recipient’s JID by extracting it from a previous message, presence request, or subscribe request.

//Build a message to reply to the user.
MessageBuilder message_builder = new MessageBuilder();
message_builder.withRecipientJids(from_jid);
message_builder.withBody(reply_body);
Message reply_message = message_builder.build();
//Send the message back to the user.
SendResponse response_status = xmpp.sendMessage(reply_message);

Remember to import the XMPP package:

import com.google.appengine.api.xmpp.*;
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Listening To XMPP Subscribe Requests

The following sample code demonstrates how to listen for incoming XMPP subscription requests. A subscription request to App Engine occurs when another XMPP client has granted access to its presence information (whether that client is available to chat or not).

This function reads in the incoming XMPP request, extracts the user name of the client and the subscription type, then records the request into logging. In a production application this code could be modified to store subscription requests into the datastore, creating a list of XMPP users interested in talking to the application.

public void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws IOException {
    //Acquire access to GAE's XMPP service.
    XMPPService xmpp = XMPPServiceFactory.getXMPPService();
    //Parse the user's subscription from the HTTP request.
    Subscription subscribe = xmpp.parseSubscription(req);
    JID from_jid = subscribe.getFromJid();
    SubscriptionType subscribe_type = subscribe.getSubscriptionType();
    //Log the subscription type.
    System.out.println(from_jid + " has subscription type " + subscribe_type);
}//end doPost

Remember to import App Engine’s XMPP package:

import com.google.appengine.api.xmpp.*;
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Enabling XMPP Services

The following XML snippet enables an application to receive XMPP messages. Insert it into the middle of the appengine-web.xml file in the /war/WEB-INF/ folder:

<!-- Enable all inbound services. -->
<inbound-services>
    <service>xmpp_message</service>
    <service>xmpp_presence</service>
    <service>xmpp_subscribe</service>
    <service>xmpp_error</service>
</inbound-services>