Java – Convert Map to JSON

[code lang=”java”]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));
}
}

}[/code]

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 – Convert JSON to MongoDB Object

JSON Data to Convert:

{
‘name’ : ‘javac’,
‘age’ : 6
}

Conversion Code:
[code lang=”java”]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();
}
}

}[/code]

Output:

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

Java – Read JSON Data Simple Example

In below example, it uses JSONParser to read and display JSON data from a file named “test.json“ using JSON.simple, a simple Java library for JSON processing.
[code lang=”java”]
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class JsonSimpleExample {
public static void main(String[] args) {

JSONParser parser = new JSONParser();

try {

Object obj = parser.parse(new FileReader("c:\\test.json"));

JSONObject jsonObject = (JSONObject) obj;

String name = (String) jsonObject.get("name");
System.out.println(name);

long age = (Long) jsonObject.get("age");
System.out.println(age);

// loop array
JSONArray msg = (JSONArray) jsonObject.get("messages");
Iterator&lt;String&gt; iterator = msg.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}

} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ParseException e) {
e.printStackTrace();
}

}

}
[/code]
Output:

prasanna
25
msg 1
msg 2
msg 3