A simple MongoDB snippet detailing some common functions used when integrating MongoDB in a Java application.

MongoDB.java

import com.mongodb.MongoClient;
import com.mongodb.MongoException;
import com.mongodb.WriteConcern;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
import com.mongodb.DBCursor;
import com.mongodb.ServerAddress;

import java.util.Arrays;

public class MongoDB {

  // To directly connect to a single MongoDB server (note that this will not auto-discover the primary even
  // if it's a member of a replica set:
  MongoClient mongoClient = new MongoClient();
  // or
  MongoClient mongoClient = new MongoClient( "localhost" );
  // or
  MongoClient mongoClient = new MongoClient( "localhost" , 27017 );
  // or, to connect to a replica set, with auto-discovery of the primary, supply a seed list of members
  MongoClient mongoClient = new MongoClient(Arrays.asList(new ServerAddress("localhost", 27017),
                                        new ServerAddress("localhost", 27018),
                                        new ServerAddress("localhost", 27019)));
  
  DB db = mongoClient.getDB( "mydb" );
  
  // Authentication
  boolean auth = db.authenticate(myUserName, myPassword);
  
  // Get a list of collections
  Set<String> colls = db.getCollectionNames();
  
  for (String s : colls) {
      System.out.println(s);
  }
  
  // Get a specific collection
  DBCollection coll = db.getCollection("testCollection");
  
  // Insert a document in a collection
  BasicDBObject doc = new BasicDBObject("name", "MongoDB").
                                append("type", "database").
                                append("count", 1).
                                append("info", new BasicDBObject("x", 203).append("y", 102));
  
  coll.insert(doc);
  
  // Find the first document in a collection
  DBObject myDoc = coll.findOne();
  
  // Get the amount of documents in a collection
  System.out.println(coll.getCount());
  
  // Iterate over a number of documents in a collection
  // The find() method can be used to narrow down the selection of documents used
  DBCursor cursor = coll.find();
  try {
     while(cursor.hasNext()) {
         System.out.println(cursor.next());
     }
  } finally {
     cursor.close();
  }
  
  // Get a single document using a query
  BasicDBObject query = new BasicDBObject("i", 71);
  
  cursor = coll.find(query);
  
  // Get a set of embedded documents
  
  BasicDBObject query = new BasicDBObject("j", new BasicDBObject("$ne", 3)).
                                        append("k", new BasicDBObject("$gt", 10));

  cursor = coll.find(query);

  // Get a set of documents
  query = new BasicDBObject("i", new BasicDBObject("$gt", 50));  // e.g. find all where i > 50
  
  cursor = coll.find(query);
  
  // or
  
  query = new BasicDBObject("i", new BasicDBObject("$gt", 20).
                                                 append("$lte", 30));  // i.e.   20 < i <= 30
  cursor = coll.find(query);
  
  // Create an index
  coll.createIndex(new BasicDBObject("i", 1));  // create index on "i", ascending
  
  // Get a list of indexes from a collection
  List<DBObject> list = coll.getIndexInfo();
  
  for (DBObject o : list) {
     System.out.println(o);
  }
  
  // Get a list of databases
  MongoClient mongoClient = new MongoClient();
  
  for (String s : mongoClient.getDatabaseNames()) {
     System.out.println(s);
  }
  
  // Drop a database
  MongoClient mongoClient = new MongoClient();
  mongoClient.dropDatabase("myDatabase");
}