ObjectMapper抛出NullPointerException

Question

这是我的代码：

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();
}

但这抛出了一个NullPointerException，我不知道原因。

Answer 1

你需要初始化你的映射器/写入器：

   //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);
    }

你的代码：

//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();
}