MongoDB: Basics with java

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Now in this post we’ll see how to create database, collection, accessing documents from collection, and other CRUD operation and useful function using Java.

Prerequisites

For demo you need to add Java driver for MongoDB in your classpath.

You can download a driver from official MongoDB site.

For all demos in http://kode12.com we are using mongo-2.10.1.jar.

Connect to server

To connect with Mongo Server you can use either MongoClient or Mongo object.

Here we are using MongoClient.
Java Code:

MongoClient mongo = new MongoClient("localhost", 27017);

For basics you have to give a port on which server is listening and server ip/computer name or localhost if server is in local machine.

Creating Database

Example:

DB db = mongo.getDB("kode12");

here getDB(String dbName) method returns object of class DB.

In this case if database “kode12” already exist than it’ll return as it is. Otherwise create an empty Database with same name and return.

> show dbs;
kode12  (empty)
local   0.078125GB
>

Java Code:

public static void main(String[] args) {
	try {
		// connect to mongo server
		MongoClient mongo = new MongoClient("localhost", 27017);

		// create a blank database
		DB db = mongo.getDB("kode12");

		// display statistics
		System.out.println(db.getStats());
	} catch (UnknownHostException e) {
		System.out.println("Error in creating database.");
		e.printStackTrace();
	}
}

Output:

{ “serverUsed” : “localhost/127.0.0.1:27017″ , “db” : “kode12″ , “collections” : 0 , “objects” : 0 , “avgObjSize” : 0.0 , “dataSize” : 0 , “storageSize” : 0 , “numExtents” : 0 , “indexes” : 0 , “indexSize” : 0 , “fileSize” : 0 , “nsSizeMB” : 0 , “dataFileVersion” : { } , “ok” : 1.0}

Creating Collection and Insert Document

Using java you have to get DBCollection object using object of class DB like,

DBCollection collection = db.getCollection("posts");

This will return object of class DBCollection which is point to give collection of given database, now you can do all operation on collection.

MongoDB Command
> db.post.insert({“title”: “1. MongoDB basic setup on windows”, “author”: “vishal”});

In shell we write String to insert in { … }, but in java you have to create BasicDBObject instance.

BasicDBObject behave likeMap, it store data in Key Value pair.

There are many way to create BasicDBObject like you also can create BasicDBObject byMap. you can refer API for more.

Now you can use save(DBObject dbObject) or insert(DBObject dbObject) method to insert given object in database.The difference between save(…) and insert(..) is what we noticed is save has limited no of function while insert has many choice to insert data like insert(List), insert(DBObject[], WriteConcern) etc… .

Note: save and insert method’s signature is DBObject so don’t get confused, DBObject is Interface and BasicDBObjectis Implementing Class of DBObject.

Java Code:

public static void main(String[] args) {
	try {
		// connect to mongo server
		MongoClient mongo = new MongoClient("localhost", 27017);

		DB db = mongo.getDB("kode12");

		BasicDBObject dbObjectInsert = new BasicDBObject();
		dbObjectInsert.append("title", "1. MongoDB basic setup on windows");
		dbObjectInsert.append("author", "vishal");

		DBCollection collection = db.getCollection("posts");
		collection.insert(dbObjectInsert);

	} catch (UnknownHostException e) {
		e.printStackTrace();
	}
}

Retrieving Document

MongoDB method : find()

> db.post.find();

{ “_id” : ObjectId(“534cb58b7c01221db59db194″), “title” : “1. basic setup on windows”, “author” : “vishal” }

>

MySQL equivalent : SELECT * FROM post;
To retrieve using java again you have to Create object of implementing class of interface DBObject (for ex, BasicDBObject) or implement DBObject interface using its all implementing class.

When you use find() method than its return object of DBCursor class. Which is similar like List<?> so can iterate and get all returned DBObject. Refer below code.

// get all document in collection
DBCursor cursor = collection.find();
while (cursor.hasNext()) {
	System.out.println(cursor.next());
}

This’ll return all document stored in collection post.

MongoDB method: findOne()

MySQL equivalent: SELECT * FROM post LIMIT 1;

In Java findOne() return only one Document so you can direct get into DBObject. Refer code.

// get first document in collection
DBObject dbObject = collection.findOne();
System.out.println(dbObject);

Conditional Retrieving

You can use condition while retrieving documents. Suppose I want to get all post whose author is vishal.

MySQL equivalent: SELECT * FROM post where author=’vishal’;

MongoDB equivalent: db.post.find({“author”: “vishal”});

Java Code:

// get all document where author is vishal
BasicDBObject findObject = new BasicDBObject();
findObject.put("author", "vishal");
DBCursor findQuery = collection.find(findObject);
while (findQuery.hasNext()) {
	System.out.println(findQuery.next());
}

Updating Document

MySQL equivalent: UPDATE post set author=’yogeshm’ WHERE title=’ 2;

MongoDB equivalent: db.post.update({“title”: “2. MongoDB Basics with Shell”}, {$set: {“author”: “yogeshm”}})

Java Code:

public static void main(String[] args) {
	try {
		MongoClient mongo = new MongoClient("localhost", 27017);

		DB db = mongo.getDB("kode12");
		// get collection
		DBCollection collection = db.getCollection("posts");

		// get post where title is "2. MongoDB basic setup on linux"
		BasicDBObject searchUpdate = new BasicDBObject();
		searchUpdate.append("title", "2. MongoDB basic setup on linux");

		// change author name from "yogesh" to "yogeshm"
		BasicDBObject basicDBObjectUpdate = new BasicDBObject();
		basicDBObjectUpdate.append("$set", new BasicDBObject("author","yogeshm"));

		// update document in collection
		collection.update(searchUpdate, basicDBObjectUpdate);

	} catch (UnknownHostException e) {
		System.out.println("Error in creating database.");
		e.printStackTrace();
	}
}

Here we create 2 instance of BasicDBObject, one is for searching for given condition and another is with new value which needs to be update.

And used update(DBObject, DBObject) method of collection.

Removing Document

MySQL equivalent: DELETE FROM post WHERE author=’vishal’;

MongoDB equivalent: db.post.remove({“author”: “vishal”});

Java Code:

public static void main(String[] args) {
	try{
	MongoClient mongo = new MongoClient("localhost", 27017);

	DB db = mongo.getDB("kode12");

	//get collection
	DBCollection collection=db.getCollection("posts");

	//remove all document where author is vishal
	BasicDBObject  removeObject = new BasicDBObject();
	removeObject.append("author","vishal");

	//remove document in  collection
	collection.remove(removeObject);

	//remove all document
	collection.remove(new BasicDBObject());

	} catch (UnknownHostException e) {
		System.out.println("Error in creating database.");
		e.printStackTrace();
	}
}

MongoDB equivalent: db.dropDatabase();

Java Code:

public static void main(String[] args) {
	try {
		MongoClient mongo = new MongoClient("localhost", 27017);

		DB db = mongo.getDB("kode12");
		db.dropDatabase();
	} catch (UnknownHostException e) {
		e.printStackTrace();
	}
}
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