RecurringTest.java

import static junit.framework.Assert.assertEquals;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.net.URISyntaxException;
import java.text.ParseException;

import net.fortuna.ical4j.data.CalendarBuilder;
import net.fortuna.ical4j.data.CalendarOutputter;
import net.fortuna.ical4j.data.CalendarParserImpl;
import net.fortuna.ical4j.data.ParserException;
import net.fortuna.ical4j.model.Calendar;
import net.fortuna.ical4j.model.Date;
import net.fortuna.ical4j.model.Property;
import net.fortuna.ical4j.model.PropertyList;
import net.fortuna.ical4j.model.Recur;
import net.fortuna.ical4j.model.component.VEvent;
import net.fortuna.ical4j.model.property.DtEnd;
import net.fortuna.ical4j.model.property.DtStart;
import net.fortuna.ical4j.model.property.ExDate;
import net.fortuna.ical4j.model.property.ProdId;
import net.fortuna.ical4j.model.property.RRule;
import net.fortuna.ical4j.model.property.Version;

import org.junit.Test;

import cloudfinder.core.lang.Sneak;

public class RecurringTest {

    @Test
    public void test() throws URISyntaxException, IOException, ParserException, ParseException {

        // Prepare calendar with recurring event
        Calendar calendar = new Calendar();
        calendar.getProperties().add(new ProdId("test"));
        calendar.getProperties().add(Version.VERSION_2_0);
        VEvent event = new VEvent();

        boolean useUtc = true;

        DtStart startDate = new DtStart(new Date("20130304"), useUtc);
        event.getProperties().add(startDate);

        DtEnd endDate = new DtEnd(new Date("20130305"), useUtc);
        event.getProperties().add(endDate);

        // Repeat every monday
        Recur recur = new Recur("FREQ=WEEKLY;BYDAY=MO");
        RRule rule = new RRule(recur);
        event.getProperties().add(rule);

        // Except for 11 March 2013
        ExDate exDate = new ExDate();
        exDate.setUtc(useUtc);
        exDate.getDates().add(new Date("20130311", "yyyyMMdd"));
        exDate.getParameters().add(net.fortuna.ical4j.model.parameter.Value.DATE);
        event.getProperties().add(exDate);

        calendar.getComponents().add(event);

        // Write to file
        File calendarFile = writeCalendarToFile(calendar);
        System.out.println("Created file: " + calendarFile.getAbsolutePath());

        /*
        File will look like this:
        ---
        BEGIN:VCALENDAR
        PRODID:test
        VERSION:2.0
        BEGIN:VEVENT
        DTSTAMP:20130327T124246Z
        DTSTART;VALUE=DATE:20130304
        DTEND;VALUE=DATE:20130305
        RRULE:FREQ=WEEKLY;BYDAY=MO
        EXDATE;VALUE=DATE:20130311T010000   <-- NOTE: time value added!
        END:VEVENT
        END:VCALENDAR
        ---
        */

        // Read from file
        FileInputStream input = new FileInputStream(calendarFile);

        // Create calendar object from file
        Calendar calendarFromFile = new CalendarBuilder(new CalendarParserImpl()).build(input);

        // Verify
        VEvent e = (VEvent) calendarFromFile.getComponents().get(0);
        PropertyList exDates = e.getProperties(Property.EXDATE);
        ExDate ex = (ExDate) exDates.get(0);
        assertEquals("EXDATE", ex.getName());
        assertEquals("20130311", ex.getValue());
    }

    public File writeCalendarToFile(Calendar calendar) {
        File file;
        try {
            file = File.createTempFile("cal", ".ics");
            FileWriter fw = new FileWriter(file);
            new CalendarOutputter().output(calendar, fw);
            fw.close();
        } catch (Exception e) {
            throw Sneak.unwrappedException(e);
        }
        return file;
    }
}

I found a workaround. Replacing lines 55-60 with this makes the test pass:

// Except for 11 March 2013
DateList dateList = new DateList(Value.DATE);
dateList.add(new Date("20130311", "yyyyMMdd"));
ExDate exDate = new ExDate(dateList);
event.getProperties().add(exDate);