How do I connect to a MongoDB Database?

In the previous post you have seen how we installed the MongoDB database server and try to use the MongoDB shell to manipulate collections in the database. You also have been introduced how to obtain and setup the MongoDB Java Driver that we can use to manipulate the MongoDB database from a Java program. Starting from this post we will begin to explore more on how to use the power of MongoDB Java Driver to work with MongoDB. You will see how we are connect to the database, how to do a CRUD operation (Create, Read, Update and Delete) with Java Driver. But first let see how we create a connection to a database in MongoDB.

Here is our first code snippet, it shows you how to bootstrap the MongoDB to open a connection to a database.

What you can see from the code above is. First we bootstrap the MongoDB by create an instance of MongoClient. Here we pass a ServerAddress to define the address of our MongoDB database with information about the host name and the port number. If you just create an instance of MongoClient without any arguments it will use the default address such as localhost for the host and 27017 as the default port number. Creating an instance of MongoClient can produce an UnknownHostException, so we need to place it inside a try-catch statement.

After initialize the MongoClient we can connect to a database by calling the getDB() method and passing the database name as argument. In the example above we connect to the school database, the database in MongoDB is represented by the DB class in the com.mongodb package. In the next line after connected to the database you can see that we are getting the students collection from this database. Just for the purpose of this example we then empty the students collection using the remove() method of the DBCollection class.

In the next lines until the end of a code snippet you can see that we populate some random data into the students collections. We call the DBCollection.insert() method to insert documents into the students collection. And finally we read the inserted documents from the students collection using the find() method and iterate the returned cursor one by one until all documents printed on the console. You can also see that we are using the try-with-resource syntax in this code as the DBCursor is already implementing the Java 7 AutoCloseable interface.

And here are the sample of the result produced by our code above.

 

Introduction to MongoDB Java Driver

In the past post Installing and Running MongoDB in Windows 7, you’ve seen how to install and running MongoDB database server. Now we are going to learn how to use the MongoDB Java Driver to access collections from the MongoDB database. To demonstrate this I am going to use Maven and and IntelliJ IDEA. You can use other IDE of your choice of course, such as Eclipse or NetBeans which also support Maven.

Let’s begin by creating our project in IntelliJ IDEA. I am going to use the community edition of IntelliJ IDEA which is free to download. Here are the steps for creating a Maven project in IntelliJ IDEA.

Creating Maven Project

  • Start IntelliJ IDEA. From the Welcome Screen select Create New Project.
  • A New Project wizard will be shown. Select Maven on the Sidebar, check the Create from archetype check box and select maven-archetype-quickstart.

    Maven Create from Archetype

    Maven Create from Archetype

  • Press the Next button to continue.
  • In the next screen you can enter the Maven project information details including the GroupId, ArtifactId, and Version.

    Maven Project Information

    Maven Project Information

  • Press the Next button to continue.
  • In this screen you can override any Maven configuration setting if you want. And you also see the summary of Maven project to be created. We do not modify the setting in this screen.

    Maven Project Summary

    Maven Project Summary

  • Press the Next button to continue.
  • In the final screen we input the Project name and Project location directory.
  • After you input these two information click the Finish button to generate the Maven project in IntelliJ IDEA.

    Maven Project Name and Location

    Maven Project Name and Location

  • Finally you have the Maven project created in IntelliJ IDEA.
  • This is the Maven project structure generated in IntelliJ IDEA.
    IntelliJ IDEA Maven Project Structure

    IntelliJ IDEA Maven Project Structure

     

 

Editing the pom.xml File

  • To use the MongoDB Java Driver in our Java application, the first thing we need to is to add the dependency to MongoDB Java Driver in our pom.xml file.
  • Add the following dependency configuration to the pom.xml.

  •  And you’ll have the complete pom.xml file like this configuration below.

IntelliJ IDEA will download all the required dependency files from the Maven Central repository if they are not available in you local Maven repository. After configuring the Maven, we are now ready to create a simple program to find a single collection from the MongoDB database.

If you are following the last post about installing and running MongoDB that I have mention in the beginning of this article you know that we have a peopledb and persons collections in our MongoDB database. Now we are going to read it using the MongoDB Java Driver in our Java application. So lets now create the application.

Create Java A Simple MongoDB Client

  • We create our class under the org.kodejava.example.mongodb package. Right click on this package and choose New, Java Class to create a new class.
  • Type in the class name MongoDBHelloWorld, and press OK button.
  • And this is the full code snippet for the MongoDBHelloWorld class.

  •  If you run this code you will get the following output printed on the screen.

  •  This is the JSON document that we’ve store in our peopledb in the MongoDB database.

The Java class above is our first example of how to use the MongoDB Java Driver to access and read a document from the MongoDB database. I hope this example can be a good start for us to learn more about MongoDB. If you have any question just submit it in the comment section below this article. See you on the next post. Thank you!

Installing and Running MongoDB in Windows 7

What is MongoDB

In this post you will see how to install and running MongoDB database server on Windows 7. What is MongoDB? MongoDB is a NoSQL database. MongoDB is a non-relational JSON document store, a document oriented database. Non-relational means that it doesn’t support the relational algebra that most often expressed in SQL like what RDBMS such as Oracle or MySQL does. The document here is not a Microsoft Word documents or such, but it is a JSON (JavaScript Object Notation) documents.

And if you don’t know what it is look like, here are some examples of JSON documents:

Other characteristics of MongoDB are: it has a dynamic schema, it doesn’t support SQL language, it doesn’t support Joins, and it doesn’t support transactional across multiple collections.

 

MongoDB Installation

After you know a bit of MongoDB lets get started with the installation process. Here are the step by step of the MongoDB installation.

  • Downloads Windows 64-bit MongoDB installer at https://www.mongodb.org/downloads. When this post is written the binary file name for Windows 64-bit is mongodb-win32-x86_64-2008plus-2.6.3-signed.msi.
  • After you have finish the download the installer double click the file to start the installation wizard.

    Welcome to MongoDB Setup

    Welcome to MongoDB Setup

  • Press the Next button for the next screen and check I accept the terms in the License Agreement check box and press the Next button to continue.

    End-User License Agreement

    End-User License Agreement

  • The next step is to choose the setup type. There are three types of setup available, Typical, Custom and Complete. For now we will choose Complete. So click the Complete button to continued the installation process.

    Choose Setup Type

    Choose Setup Type

  • Press the Install button to begin installation process.

    Ready to Install MongoDB

    Ready to Install MongoDB

  • After pressing the Install button you can see the screen of MongoDB installation process. Wait until the installation is done.

    Installing MongoDB

    Installing MongoDB

  • And finally you have the MongoDB database installed. Click the Finish button to end the installation process.

    Completed MongoDB Instalation

    Completed MongoDB Instalation

The steps above have finalize your MongoDB installation. If you check in your C:\Program Files directory you will see the MongoDB installation directory in there. There will be a bin directory under C:\Program Files\MongoDB 2.6 Standard where all the MongoDB application files. Now you have install the database server lets run and check the database server.

 

Running MongoDB

For this step we will focus on two files from the bin directory of the MongoDB installation. The mongod.exe and mongo.exe. The first executable is the MongoDB database engine daemon while the second executable is the shell program to access the MongoDB.

To run the database do the following steps:

  • Create data directory. By default MongoDB look for \data\db directory in the root Drive from where you run the mongod. For example you can create C:\data\db. Or you can use the --dbpath argument to tell MongoDB where to store the data.
  • Open Command Prompt and cd to C:\Program Files\MongoDB 2.6 Standard\bin and type mongod to start the daemon.
    MongoDB - mongod

    MongoDB – mongod

    The screen above shows you that the MongoDB is successfully started, using the dbpath \data\db and it ready and listening for connections on the default port 27017.

 

Running The Shell

  • Open Command Prompt and cd to C:\Program Files\MongoDB 2.6 Standard\bin.
  • Run mongo.exe to start the shell. You’ll see a welcome message to the MongoDB shell.

    MongoDB - Mongo Shell

    MongoDB – Mongo Shell

  • In the shell above we run a couple of commands:
  • use peopledb command ask the MongoDB to change to the persons collections, if it doesn’t exist Mongo will create one.
  • To add document to the collections we can call db.persons.insert(); and passing the JSON document as the arguments.
  • To query the collection we can use db.persons.find();.
  • If you want for instance to find Julia in the collection you can do db.persons.find({"firstName" : "Julia"});
  • To close the shell we can call quit(); command.

That’s all for now, I hope this post is useful for you. In the next post I will show you how to create a simple Java application that use Mongo Java Driver to store data using Java programming into the MongoDB database. So, see you in the next post. Thank you.

How do I combine filter and projection operation in Spring EL?

Using Spring Expression Language (SpEL) we can filter a collection based on some criteria. We can also create a projection of a collection by collecting only a particular property from the collection objects.

Now you know that you have two good features of SpEL that are really powerful to use when working with collection objects manipulation. But you are wondering how to combine both of these filter and projection in one expression. Can you do this in Spring EL? The answer is yes! You can combine them both in one expression. Let’s see an example below.

We are going to use the same configuration used in the previous example:

In the configuration above, when we define the library bean we set its bookTitles property using the filtering and projection operator. First we take only books that have more that 250 pages and then we create the projection that contains only the book title. So this expression give us all the book’s title of a book that has more than 250 pages.

To make the example complete here again the definition of the Book and the Library class.

The main class the run the configuration file:

The result of the code snippet: