What's the best way to convert pojo to JSON in Spring

Spring boot uses Jackson libraries to convert Java POJO Object to/from Json. These converters are created and used automatically for Rest services to convert POJO object returned by Rest method to Json (e.g. Rest service methods annotated with @ResponseBody). If Rest services are used then Spring creates POJO/Json converters automatically. If you want to make POJO/Json conversion in some different case you need com.fasterxml.jackson.databind.ObjectMapper.

Avoid creating ObjectMapper instance by operator new, reuse the ObjectMapper already available in Spring application context using dependency injection annotation @Autowired.Spring will automatically inject value to your objectMapper variable.

public class clA {    @Autowired    private ObjectMapper objectMapper;    public Optional<String> objToJson(MyObj obj) {            try {                String objJackson = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj));            } catch (JsonProcessingException e) {                log.debug("failed conversion: Pfra object to Json", e);            }        });}

If you don't want to use Spring MVC to convert object to JSON string, you could do it like this:

private JsonGenerator jsonGenerator = null;private ObjectMapper objectMapper = null;public void init(){  objectMapper = new ObjectMapper();  try{     jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(System.out, JsonEncoding.UTF8);     jsonGenerator.writeObject(bean);      objectMapper.writeValue(System.out, bean);  }catch (IOException e) {        e.printStackTrace();  }  jsonGenerator.flush();  jsonGenerator.close();}

You must declare the bean like this

public class AccountBean {    private int id;    private String name;    private String email;    private String address;    private Birthday birthday;    //getters, setters    @Override    public String toString() {        return this.name + "#" + this.id + "#" + this.address + "#" + this.birthday + "#" + this.email;    }}

import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.SerializationFeature;public static String jsonToPojo(Object targetPojo) {    if(targetPojo == null)        return null;    ObjectMapper mapper = new ObjectMapper();    try {         mapper.enable(SerializationFeature.INDENT_OUTPUT);         return mapper.writeValueAsString(targetPojo);    } catch (IOException e) {        LOGGER.error("Error parsing string to json. Target pojo : {}", targetPojo.getClass().getName() );    }     return null;}