Dinesh on Java

In this tutorial we will discuss an example of java which describe how to get the collection from MongoDb and other functions of collection.

To get a collection to use, just specify the name of the collection to the getCollection(String collectionName) method:

DBCollection coll = db.getCollection("dineshonjavaCollection");

Once you have this collection object, you can now do things like insert data, query for data, etc. Suppose “dineshonjavaCollection” if this collection already created not created on the mongoDB then return the “dineshonjavaCollection” else it create new “dineshonjavaCollection” in the MongoDB.

com.mongodb.DBCollection is abstract class. This class provides a skeleton implementation of a database collection.
A typical invocation sequence is thus

Mongo mongo = new Mongo( new DBAddress( "localhost", 127017 ) );
     DB db = mongo.getDB( "dineshonjavaDB" );
     DBCollection collection = db.getCollection( "dineshonjavaCollection" );

If you do not know the collection name, use db.getCollectionNames() to get the entire list of collection names from a selected database.

DB db = mongo.getDB("dineshonjavaDB");
Set<String> collections = db.getCollectionNames();
 
for (String collectionName : collections) {
   System.out.println(collectionName);
}

If “dineshonjavaDB” contains collection name “dineshonjavaCollection”, then you will see following result :

system.indexes //system collection
system.users //system collection
dineshonjavaCollection

Full example to get collection from MongoDB, via Java driver.

package com.dineshonjava.mongo.test;

import java.net.UnknownHostException;
import java.util.Set;

import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.Mongo;
import com.mongodb.MongoException;

/**
 * @author Dinesh Rajput
 *
 */
public class CollectiomDemo {

 /**
  * @param args
  */
 public static void main(String[] args) {
  try {
   // connect to mongoDB, IP and port number
   Mongo mongo = new Mongo("localhost", 27017);
 
   // get database from MongoDB,
   // if database doesn't exists, mongoDB will create it automatically
   DB db = mongo.getDB("dineshonjavaDB");
 
   // get list of collections
   Set<String>collections = db.getCollectionNames();
 
   for (String collectionName : collections) {
    System.out.println(collectionName);
   }
   System.out.println("************************************************");   
   // Get collection from MongoDB, database named "dineshonjavaDB"
   // if collection doesn't exists, mongoDB will create it automatically
   DBCollection collection = db.getCollection("dineshonjavaCollection");
 
   System.out.println(collection);
 
   System.out.println("Done");
 
  } catch (UnknownHostException e) {
   e.printStackTrace();
  } catch (MongoException e) {
   e.printStackTrace();
  }
 
 }

}

If every thing is fine then run as a java application then we will get following output on console.

Reference
Java tutorial – MongoDB

Download Source Code + Libs
MongoDBCollectionDemo.zip