MongoDB的MapReduce简单示例（java）

1、数据准备

db.sell.insert({"price":8.0,"amount":500.0,"status":"a"})
db.sell.insert({"price":8.0,"amount":450.0,"status":"a"})
db.sell.insert({"price":8.0,"amount":400.0,"status":"a"})
db.sell.insert({"price":9.0,"amount":350.0,"status":"a"})
db.sell.insert({"price":9.0,"amount":300.0,"status":"a"})
db.sell.insert({"price":9.0,"amount":250.0,"status":"a"})
db.sell.insert({"price":9.0,"amount":200.0,"status":"a"})
db.sell.insert({"price":10.0,"amount":150.0,"status":"d"})
db.sell.insert({"price":10.0,"amount":100.0,"status":"d"})
db.sell.insert({"price":10.0,"amount":50.0,"status":"d"})
db.sell.insert({"price":10.0,"amount":0.0,"status":"d"})

2、MapReduce

	private static void testMapReduce3x()
	{
		MongoClient mongoClient = new MongoClient("localhost", 27017);
		MongoDatabase db = mongoClient.getDatabase("test");
		MongoCollection collection = db.getCollection("sell");

		String map = "function(){emit(this.price,this.amount);}";
		String reduce = "function(key, values){return Array.sum(values)}";

		MapReduceIterable out = collection.mapReduce(map, reduce);
		MongoCursor cursor = out.iterator();
		while (cursor.hasNext()) 
		{
			System.out.println(cursor.next());
		}
	}
	
	private static void testMapReduce2x()
	{
		MongoClient mongoClient = new MongoClient("localhost", 27017);
		MongoDatabase db = mongoClient.getDatabase("test");
		BasicDBObject query=new BasicDBObject("status","a");
		DBCollection dbcollection = mongoClient.getDB("test").getCollection("sell");
		
		String map = "function(){emit(this.price,this.amount);}";
		String reduce = "function(key, values){return Array.sum(values)}";
		
		MapReduceCommand cmd = new MapReduceCommand(dbcollection, map, reduce,
		    "outputCollection", MapReduceCommand.OutputType.INLINE, query);
		
		MapReduceOutput out2 = dbcollection.mapReduce(cmd);
		for (DBObject o : out2.results()) 
		{
		   System.out.println(o.toString());
		}
	}