Map reduce operation with suitable example using MongoDB

package mapreduce;

import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBObject;
import com.mongodb.MapReduceCommand;
import com.mongodb.MapReduceOutput;
import com.mongodb.MongoClient;
public class mapreduce {
public static void main(String[] args) {
// TODO Auto-generated method stub
MongoClient mongo;
try {
mongo = new MongoClient("localhost", 27017);
DB db = mongo.getDB("library");

DBCollection books = db.getCollection("books");

BasicDBObject book = new BasicDBObject();
book.put("name", "Understanding JAVA");
book.put("pages", 100);
books.insert(book);

book = new BasicDBObject();
book.put("name", "Understanding JSON");
book.put("pages", 200);
books.insert(book);

book = new BasicDBObject();
book.put("name", "Understanding XML");
book.put("pages", 300);
books.insert(book);

book = new BasicDBObject();
book.put("name", "Understanding Web Services");
book.put("pages", 400);
books.insert(book);

book = new BasicDBObject();
book.put("name", "Understanding Axis2");
book.put("pages", 150);
books.insert(book);

String map = "function() { "+
"var category; " +
"if ( this.pages >= 250 ) "+
"category = 'Big Books'; " +
"else " +
"category = 'Small Books'; "+
"emit(category, {name: this.name});}";

String reduce = "function(key, values) { " +
"var sum = 0; " +
"values.forEach(function(doc) { " +
"sum += 1; "+
"}); " +
"return {books: sum};} ";

MapReduceCommand cmd = new MapReduceCommand(books, map, reduce,
null, MapReduceCommand.OutputType.INLINE, null);

MapReduceOutput out = books.mapReduce(cmd);

for (DBObject o : out.results()) {
System.out.println(o.toString());
}
} catch (Exception e) {
//TODO Auto-generated catch block
e.printStackTrace();
}
}
}
*************************************OUTPUT*****************************************{ "_id" : "Big Books" , "value" : { "books" : 2.0}}
{ "_id" : "Small Books" , "value" : { "books" : 3.0}}