ObjectMapper throw NullPointerException

Question

This is my code:

Prueba test = new Prueba();
test.setNombre("test");
test.setApellidos("test");
test.setEdad("test");
try {
    String pruebaTest = mapper.writeValueAsString(test);
    System.out.println(pruebaTest);
} catch (JsonProcessingException e) {
    e.printStackTrace();
}

But this throw a NullPointerException, and i don't know the reason.

Answer 1

You need to initialize your mapper / writer:

   //json object to string
    ObjectMapper objectMapper = new ObjectMapper();

    ObjectWriter ow = objectMapper.writer();
    String jsonAsString;
    try {
      jsonAsString = ow.writeValueAsString(object);
    } catch (final JsonProcessingException e) {
      throw new Exception("Couldn't process object.", e);
    }

Your code:

//json object to string
ObjectMapper objectMapper = new ObjectMapper();
ObjectWriter ow = objectMapper.writer();

Prueba test = new Prueba();
test.setNombre("test");
test.setApellidos("test");
test.setEdad("test");
String pruebaTest;
try {
    pruebaTest = ow.writeValueAsString(test);
    System.out.println(pruebaTest);
} catch (JsonProcessingException e) {
    e.printStackTrace();
}