Simple example of MongoDB driver for Java

Comment.java

public class Comment {

	private final String author;
	private final String body;

	public Comment(String author, String body) {
		this.author = author;
		this.body = body;
	}

	public String getAuthor() {
		return author;
	}

	public String getBody() {
		return body;
	}

}

MongoPostTest.java

import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

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

public class MongoPostTest {

	public static void main(String[] args) throws UnknownHostException, MongoException {

		// Initialise the connection to MongoDB
		Mongo m = new Mongo("localhost", 27017);

		DB db = m.getDB("mydb");

		// Create a post and some comments to insert
		List<Comment> comments = new ArrayList<Comment>();
		comments.add(new Comment("bob", "comment 1"));
		comments.add(new Comment("alfred", "comment 2"));
		Post post = new Post(new Date(), "New blog post", "Welcome to my blog", comments);

		// Get the posts collection and store the post
		PostDAO postDAO = new PostDAO();
		postDAO.setDataSource(db);
		postDAO.storePost(post);

		// Get all posts and print them
		DBCollection postsColl = db.getCollection("posts");
		DBCursor cur = postsColl.find();
		while (cur.hasNext()) {
			System.out.println(cur.next());
		}
	}
}

Post.java

import java.util.Date;
import java.util.List;


public class Post {

	private final Date date;
	private final String title;
	private final String body;
	private final List<Comment> comments;

	public Post(Date date, String title, String body, List<Comment> comments) {
		this.date = date;
		this.title = title;
		this.body = body;
		this.comments = comments;
	}

	public Date getDate() {
		return date;
	}

	public String getTitle() {
		return title;
	}

	public String getBody() {
		return body;
	}

	public List<Comment> getComments() {
		return comments;
	}

}

PostDAO.java

import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.mongodb.BasicDBList;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;

public class PostDAO {
	
	private DB db;

	public void setDataSource(DB db) {
		this.db = db;
	}

	public void storePost(Post post) {
		DBCollection postsColl = db.getCollection("posts");
		postsColl.insert(getPostObj(post));
	}

	public DBObject getPostObj(Post post) {
		Map<String, Object> postMap = new HashMap<String, Object>();
		postMap.put("date", post.getDate());
		postMap.put("title", post.getTitle());
		postMap.put("body", post.getBody());

		List<DBObject> comments = new ArrayList<DBObject>();
		for (Comment comment : post.getComments()) {
			comments.add(getCommentObj(comment));
		}
		postMap.put("comments", comments);
		
		return new BasicDBObject(postMap);
	}

	private DBObject getCommentObj(Comment comment) {
		Map<String, Object> commentMap = new HashMap<String, Object>();
		commentMap.put("author", comment.getAuthor());
		commentMap.put("body", comment.getBody());
		return new BasicDBObject(commentMap);
	}

	public List<Post> getAllPosts(long id) {
		DBCollection postsColl = db.getCollection("posts");
		DBCursor cur = postsColl.find();

		List<Post> posts = new ArrayList<Post>();
        while(cur.hasNext()) {
            posts.add(getPost(cur.next()));
        }
        return posts;
	}

	private Post getPost(DBObject postObj) {
		Date date = (Date) postObj.get("date");
		String title = (String) postObj.get("title");
		String body = (String) postObj.get("body");

		List<Comment> comments = new ArrayList<Comment>();
		for (Object commentObj : (BasicDBList) postObj.get("comments")) {
			comments.add(getComment((DBObject) commentObj));
		}
		return new Post(date, title, body, comments);
	}

	private Comment getComment(DBObject commentObj) {
		String author = (String) commentObj.get("author");
		String body = (String) commentObj.get("body");
		return new Comment(author, body);
	}

}