How to convert hashmap to JSON object in Java

You can use:

new JSONObject(map);

Caution: This will only work for a Map<String, String>!

Other functions you can get from its documentation
http://stleary.github.io/JSON-java/index.html

Gson can also be used to serialize arbitrarily complex objects.

Here is how you use it:

Gson gson = new Gson(); String json = gson.toJson(myObject); 

Gson will automatically convert collections to JSON arrays. Gson can serialize private fields and automatically ignores transient fields.

You can convert Map to JSON using Jackson as follows:

Map<String,Object> map = new HashMap<>();//You can convert any Object.String[] value1 = new String[] { "value11", "value12", "value13" };String[] value2 = new String[] { "value21", "value22", "value23" };map.put("key1", value1);map.put("key2", value2);map.put("key3","string1");map.put("key4","string2");String json = new ObjectMapper().writeValueAsString(map);System.out.println(json);

Maven Dependencies for Jackson :

<dependency>    <groupId>com.fasterxml.jackson.core</groupId>    <artifactId>jackson-core</artifactId>    <version>2.5.3</version>    <scope>compile</scope></dependency><dependency>    <groupId>com.fasterxml.jackson.core</groupId>    <artifactId>jackson-databind</artifactId>    <version>2.5.3</version>    <scope>compile</scope></dependency>

If you are using `JSONObject` library, you can convert map to `JSON` as follows:

JSONObject Library:import org.json.JSONObject;

Map<String, Object> map = new HashMap<>();// Convert a map having list of values.String[] value1 = new String[] { "value11", "value12", "value13" };String[] value2 = new String[] { "value21", "value22", "value23" };map.put("key1", value1);map.put("key2", value2);JSONObject json = new JSONObject(map);System.out.println(json);

Maven Dependencies for `JSONObject` :

<dependency>    <groupId>org.json</groupId>    <artifactId>json</artifactId>    <version>20140107</version></dependency>

Hope this will help. Happy coding.