public static void main(String... args) throws Exception {
// Read an Atom Feed... this part isn't required.. the mapred stuff
// works on any activity stream source, this just gives us some
// interesting input material
Abdera abdera = Abdera.getInstance();
URL url = new URL("http://planet.intertwingly.net/atom.xml");
Parser parser = abdera.getParser();
ParserOptions options = parser.makeDefaultParserOptions().charset("UTF-8").get();
Document<Feed> doc = abdera.getParser().parse(url.openStream(), url.toString(), options);
Feed feed = doc.getRoot();
ByteArrayOutputStream out = new ByteArrayOutputStream();
feed.writeTo("activity", out);
// Convert it to an Activity Stream
String r = new String(out.toByteArray(), "UTF-8");
Collection<Activity> col = IO.get().readCollection(new StringReader(r));
// Prepare the input data.. here's where the interesting bit starts...
// this first step indexes the collection of activities into a Iterable
// of Pair objects. A Pair object is essentially a tuple with two elements,
// called first() and second(). The first() is used as the key in the
// Map function, while second() is used as the value. In this particular
// case, we're using a null key on the input...
PairBuilder<Void, Activity> gen =
Pair.<Void, Activity>make().index(MoreFunctions.<Activity>alwaysVoid(), col.getItems());
// The Function ff is asynchronous... we apply it, then call get on
// the returned Future to wait for the result. The mapreduce operation
// occurs in a different thread and sets the value of the Future
// when it is complete... once it does, we iterate through the collection
// of Pairs it kicks out.. which in this case, is a listing of actors
// in the stream sorted by number of activities each.
for (Pair<Integer, Iterable<String>> entry : ff.apply(gen).get())
System.out.println(entry.first() + "=" + entry.second());
}
@Test
public void testPair() {
Pair<String, String> pair = Pair.of("A", "B");
assertEquals("A", pair.first());
assertEquals("B", pair.second());
Map<String, String> map = new HashMap<String, String>();
map.put("A", "B");
map.put("B", "C");
Iterable<Pair<String, String>> pairs = Pair.from(map);
assertEquals(2, Iterables.size(pairs));
assertEquals("A", Iterables.get(pairs, 0).first());
assertEquals("B", Iterables.get(pairs, 0).second());
assertEquals("B", Iterables.get(pairs, 1).first());
assertEquals("C", Iterables.get(pairs, 1).second());
}