Categories: MongoDB

Java MongoDB Get Collection from Database

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.

output:
dineshonjavaCollection
employees
system.indexes
************************************************
dineshonjavaCollection
Done

Reference
Java tutorial – MongoDB

Download Source Code + Libs
MongoDBCollectionDemo.zip

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!

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