Convert JSON to Map

What is the best way to convert a JSON code as this:

{ 
    'data' : 
    { 
        'field1' : 'value1', 
        'field2' : 'value2'
    }
}

in a Java Map in which one the keys are (field1, field2) and the values for those fields are (value1, value2).

Any ideas? Should I use Json-lib for that? Or better if I write my own parser?

Answers:

The JsonTools library is very complete. It can be found at Github.

Answers:

I hope you were joking about writing your own parser. :-)

For such a simple mapping, most tools from http://json.org (section java) would work. For one of them (Jackson https://github.com/FasterXML/jackson-databind/#5-minute-tutorial-streaming-parser-generator), you'd do:

Map<String,Object> result =
        new ObjectMapper().readValue(JSON_SOURCE, HashMap.class);

(where JSON_SOURCE is a File, input stream, reader, or json content String)

Answers:

JSON to Map always gonna be a string/object data type. i haved GSON lib from google.

works very well and JDK 1.5 is the min requirement.

Answers:

Use JSON lib E.g. http://www.json.org/java/

// Assume you have a Map<String, String> in JSONObject jdata
@SuppressWarnings('unchecked')
Iterator<String> nameItr = jdata.keys();
Map<String, String> outMap = new HashMap<String, String>();
while(nameItr.hasNext()) {
    String name = nameItr.next();
    outMap.put(name, jdata.getString(name));

}

Answers:

Using the GSON library:

import com.google.gson.Gson;
import com.google.common.reflect.TypeToken;
import java.lang.reclect.Type;

Use the following code:

Type mapType = new TypeToken<Map<String, Map>>(){}.getType();  
Map<String, String[]> son = new Gson().fromJson(easyString, mapType);

Answers:

I like google gson library.
When you don't know structure of json. You can use

JsonElement root = new JsonParser().parse(jsonString);

and then you can work with json. e.g. how to get 'value1' from your gson:

String value1 = root.getAsJsonObject().get('data').getAsJsonObject().get('field1').getAsString();

Answers:

This way its works like a Map...

JSONObject fieldsJson = new JSONObject(json);
String value = fieldsJson.getString(key);

<dependency>
    <groupId>org.codehaus.jettison</groupId>
    <artifactId>jettison</artifactId>
    <version>1.1</version>
</dependency>

Answers:

java.lang.reflect.Type mapType = new TypeToken<Map<String, Object>>(){}.getType();
Gson gson = new Gson();
Map<String, Object> categoryicons = gson.fromJson(json, mapType );

Answers:

My post could be helpful for others, so imagine you have a map with a specific object in values, something like that:

{  
   'shopping_list':{  
      '996386':{  
         'id':996386,
         'label':'My 1st shopping list',
         'current':true,
         'nb_reference':6
      },
      '888540':{  
         'id':888540,
         'label':'My 2nd shopping list',
         'current':false,
         'nb_reference':2
      }
   }
}

To parse this JSON file with GSON library, it's easy : if your project is mavenized

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.3.1</version>
</dependency>

Then use this snippet :

import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;

//Read the JSON file
JsonElement root = new JsonParser().parse(new FileReader('/path/to/the/json/file/in/your/file/system.json'));

//Get the content of the first map
JsonObject object = root.getAsJsonObject().get('shopping_list').getAsJsonObject();

//Iterate over this map
Gson gson = new Gson();
for (Entry<String, JsonElement> entry : object.entrySet()) {
    ShoppingList shoppingList = gson.fromJson(entry.getValue(), ShoppingList.class);
    System.out.println(shoppingList.getLabel());
}

The corresponding POJO should be something like that :

public class ShoppingList {

    int id;

    String label;

    boolean current;

    int nb_reference;

    //Setters & Getters !!!!!
}

Hope it helps !

Answers:

Underscore-java library can convert json string to hash map. I am the maintainer of the project.

Code example:

import com.github.underscore.lodash.U;
import java.util.*;

public class Main {

    @SuppressWarnings('unchecked')
    public static void main(String[] args) {
        String json = '{'
            + '    'data' :'
            + '    {'
            + '        'field1' : 'value1','
            + '        'field2' : 'value2''
            + '    }'
            + '}';

       Map<String, Object> data = (Map) U.get((Map<String, Object>) U.fromJson(json), 'data');
       System.out.println(data);

       // {field1=value1, field2=value2}
    }
}

Answers:

One more alternative is json-simple which can be found in Maven Central:

(JSONObject)JSONValue.parse(someString); //JSONObject is actually a Map.

The artifact is 24kbytes, doesn't have other runtime dependencies.

Answers:

With google's Gson 2.7 (probably earlier versions too, but I tested 2.7) it's as simple as:

Map map = gson.fromJson(json, Map.class);

Which returns a Map of type class com.google.gson.internal.LinkedTreeMap and works recursively on nested objects.

Answers:

I do it this way. It's Simple.

import java.util.Map;
import org.json.JSONObject;
import com.google.gson.Gson;

public class Main {
    public static void main(String[] args) {
        JSONObject jsonObj = new JSONObject('{ 'f1':'v1'}');
        @SuppressWarnings('unchecked')
        Map<String, String> map = new Gson().fromJson(jsonObj.toString(),Map.class);
        System.out.println(map);
    }
}

Answers:

import net.sf.json.JSONObject

JSONObject.fromObject(yourJsonString).toMap

Answers:

If you need pure Java without any dependencies, you can use build in Nashorn API from Java 8. It is deprecated in Java 11.

This is working for me:

...
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
...

public class JsonUtils {

    public static Map parseJSON(String json) throws ScriptException {
        ScriptEngineManager sem = new ScriptEngineManager();
        ScriptEngine engine = sem.getEngineByName('javascript');

        String script = 'Java.asJSONCompatible(' + json + ')';

        Object result = engine.eval(script);

        return (Map) result;
    }
}

Sample usage

JSON:

{
    'data':[
        {'id':1,'username':'bruce'},
        {'id':2,'username':'clark'},
        {'id':3,'username':'diana'}
    ]
}

Code:

...
import jdk.nashorn.internal.runtime.JSONListAdapter;
...

public static List<String> getUsernamesFromJson(Map json) {
    List<String> result = new LinkedList<>();

    JSONListAdapter data = (JSONListAdapter) json.get('data');

    for(Object obj : data) {
        Map map = (Map) obj;
        result.add((String) map.get('username'));
    }

    return result;
}

Answers:

If you're using org.json, JSONObject has a method toMap(). You can easily do:

Map<String, Object> myMap = myJsonObject.toMap();

Answers:

Try this code:

  public static Map<String, Object> convertJsonIntoMap(String jsonFile) {
        Map<String, Object> map = new HashMap<>();
        try {
            ObjectMapper mapper = new ObjectMapper();
            mapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
            mapper.readValue(jsonFile, new TypeReference<Map<String, Object>>() {
            });
            map = mapper.readValue(jsonFile, new TypeReference<Map<String, String>>() {
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
        return map;
    }

Answers: