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value not injecting in @ReuqestBody POJO from application-dev.properties – SpringBoot Application

I am new to Java SpringBoot and I am trying to inject a default value from application-dev.properties file. Basically, the idea is to set default value to RequestObject’s id property, default value being injected(/fetched) from application-dev.properties.

UseCase: In case, no data or blank data is being passed in request body of API, the code should set a default value (being injected/fetched from application-dev.properties).

Controller Code

@RequestMapping(value = PATH, method = RequestMethod.POST, consumes = MediaType.APPLICATION_JSON_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
private @ResponseBody ResponseEntity<ResponseBean<ResponseObject>> postController(
    final @Valid @RequestBody RequestObject request) throws Exception {
return serviceClass.service(request);
}

I did the following in RequestObject Class code

public class RequestObject {

    @Value("${package.default}")
    private String default_id;
    private String id = default_id;
    
    public String getId() {
     return id;
}

public void setId(String id) {
    this.id = !StringUtils.isBlank(id) ? id : default_id;
}

The above code is not working. Please help or suggest a better way to achieve the requirement.

Note: If I hardcode the id value like id=”abcd” while defining & in setter method, the code is working.

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Answer

You can inject stuff(default values from application properties, other beans, etc.) only in spring managed components – those are classes annotated with @Component, @Service etc.

RequestObject, being a class you map request body to, is not, and should not be a component.

In order to inject default value from application.properties you need custom deserializer, which is a bean, and register this deserializer with ObjectMapper.

@Component
public class RequestObjectDeserializer extends StdDeserializer<RequestObject> {

    @Value("${your.property.here}")
    private String defaultValue;

    public RequestObjectDeserializer() {
        super(RequestObject.class);
    }

    @Override
    public RequestObject deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JacksonException {
        //deserialize
    }
}

Then register it with already existing Objectmapper:

@Autowired
public void configObjectMapper(ObjectMapper objectMapper, RequestObjectDeserializer deserializer) {
    SimpleModule module = new SimpleModule();
    module.addDeserializer(RequestObject.class, deserializer);
    objectMapper.registerModule(module);
}

You can add above in any @Configuration class.

I’d say keeping the default value as static field in RequestObject, and having the logic in setter, is better in this case.

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