Simple caldav4j example in java and clojure

I was trying to access a caldav calendar through java and clojure to build a small application. But it wasn’t too easy.

caldav4j seemed to be very confusing and not so well maintained. There is no quick start guide and you are directed to have a look at the unit tests. But they are a compilation of interconnected classes and their hierarchies including a lot of deprecated classes being used – pretty confusing for a newcomer.

I had also problems using the alternative ical4j and it’s caldav connector. After some debugging it seemed incompatible with zimbra because of some strange filter constraints.

This might all be due to the fact that caldav is a complex protocol and I accepted to dig deeper into caldav4j.

Enough of the yacking, I traced down the necessary wire to build a basic example and hope it’ll help others looking for a quick start.

Java: https://github.com/dedeibel/list-events-caldav4j-example

Clojure: https://github.com/dedeibel/list-events-caldav4j-example-clojure

I tested it with zimbra. For google calendar a little more work might be required. The key might be in the GoogleCalDavDialect.java class.

 
Java:
 

    HttpClient httpClient = new HttpClient();
    // I tried it with zimbra - but I had no luck using google calendar
    httpClient.getHostConfiguration().setHost("CALDAVHOST", 443, "https");
    String username = "username";
    UsernamePasswordCredentials httpCredentials = new UsernamePasswordCredentials(username, "secret");
    httpClient.getState().setCredentials(AuthScope.ANY, httpCredentials);
    httpClient.getParams().setAuthenticationPreemptive(true);
    // Need a proxy?
    //httpClient.getHostConfiguration().setProxy("phost", 8080);

    CalDAVCollection collection = new CalDAVCollection(
        "/dav/"+ username +"/Calendar",
        (HostConfiguration) httpClient.getHostConfiguration().clone(),
        new CalDAV4JMethodFactory(),
        CalDAVConstants.PROC_ID_DEFAULT
        );

    GenerateQuery gq=new GenerateQuery();
    // TODO you might want to adjust the date
    gq.setFilter("VEVENT [20131001T000000Z;20131010T000000Z] : STATUS!=CANCELLED");
    // Get the raw caldav query
    // System.out.println("Query: "+ gq.prettyPrint());
    CalendarQuery calendarQuery = gq.generate();
    List<Calendar>calendars = collection.queryCalendars(httpClient, calendarQuery);

    for (Calendar calendar : calendars) {
      ComponentList componentList = calendar.getComponents().getComponents(Component.VEVENT);
      Iterator<VEvent> eventIterator = componentList.iterator();
      while (eventIterator.hasNext()) {
        VEvent ve = eventIterator.next();
        System.out.println("Event: "+ ve.toString());
        System.out.println("\n\n");
      }
    }

 
Clojure:
 

defn- create-query []
  (let [gq (GenerateQuery.)]
    ; Date Format yyyyMMdd
    (.setFilter gq "VEVENT [20131001T000000Z;20131010T000000Z] : STATUS!=CANCELLED")
    (.generate gq)))

(defn -main []
  (let [http-client (initialize-http-client)
        collection-path (:collection-path configuration)
        host-configuration (.clone (.getHostConfiguration http-client))
        method-factory (CalDAV4JMethodFactory.)
        collection (CalDAVCollection. collection-path host-configuration method-factory CalDAVConstants/PROC_ID_DEFAULT)
        calendars (.queryCalendars collection http-client (create-query))
        ]
    (doseq [cal calendars
            event (-> cal (.getComponents) (.getComponents Component/VEVENT))]
      (println "Event: " event)
      (println "\n\n"))))
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