Java – Convert Map to JSON

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

public class MapToJson {

	public static void main(String[] args) {
		Map<String, String> colours = new HashMap<String, String>();
		colours.put("BLACK", "#000000");
		colours.put("RED", "#FF0000");
		colours.put("GREEN", "#008000");
		colours.put("BLUE", "#0000FF");
		colours.put("YELLOW", "#FFFF00");
		colours.put("WHITE", "#FFFFFF");

		//
		// Convert a Map into JSON string.
		//
		Gson gson = new Gson();
		String json = gson.toJson(colours);
		System.out.println("json = " + json);

		//
		// Convert JSON string back to Map.
		//
		Type type = new TypeToken<Map<String, String>>(){}.getType();
		Map<String, String> map = gson.fromJson(json, type);
		for (String key : map.keySet()) {
			System.out.println("map.get = " + map.get(key));
		}
	}

}

Output:

json = {“WHITE”:”#FFFFFF”,”BLUE”:”#0000FF”,”YELLOW”:”#FFFF00″,”GREEN”:”#008000″,”BLACK”:”#000000″,”RED”:”#FF0000″}
map.get = #FFFFFF
map.get = #0000FF
map.get = #FFFF00
map.get = #008000
map.get = #000000
map.get = #FF0000

Java MongoDB – Get Collection from Database

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

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

public class GetCollectionApp {

	public static void main(String[] args) {
		try {
			Mongo mongo = new Mongo("localhost", 27017);
			DB db = mongo.getDB("yourdb");

			// get entire list of collections
			Set<String> collections = db.getCollectionNames();

			for (String collectionName : collections) {
				System.out.println(collectionName);
			}

			// get a single collection
			DBCollection collection = db.getCollection("yourCollection");
			System.out.println(collection.toString());

			System.out.println("Done");

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

}

Java – Convert JSON to MongoDB Object

JSON Data to Convert:

{
‘name’ : ‘javac’,
‘age’ : 6
}

Conversion Code:

import java.net.UnknownHostException;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.Mongo;
import com.mongodb.MongoException;
import com.mongodb.util.JSON;

public class App {

	public static void main(String[] args) {
		try {

			Mongo mongo = new Mongo("localhost", 27017);
			DB db = mongo.getDB("yourdb");
			DBCollection collection = db.getCollection("dummyColl");

			// convert JSON to DBObject directly
			DBObject dbObject = (DBObject) JSON.parse("{'name':'javac', 'age':6}");

			collection.insert(dbObject);

			DBCursor cursorDoc = collection.find();
			while (cursorDoc.hasNext()) {
				System.out.println(cursorDoc.next());
			}

			System.out.println("Done");

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

}

Output:

{ “_id” : { “$oid” : “4dc9ebb5237f275c2fe4959f”} , “name” : “javac” , “age” : 6}
Done

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