Sending #Value annotated fields to a DTO layer returns null - spring-boot

Question

I have a class which is composed of 2 different objects :
public class MyClass{
private OptionClass optionClass;
private ConstantClass constantClass;
public DocumentToSignRestRequest(OptionClass optionClass, ConstantClass constantClass) {
this.optionClass= optionClass;
this.constantClass= constantClass;
}
}
My first class is a classic POJO. My second class retrieve values from the application.properties file.
public class ConstantClass {
#Value("${api.url}")
private String hostName;
#Value("${sign.path}")
private String pathStart;
public ConstantClass () {
this.hostName= getHostName();
this.path = getPath();
}
I map MyClass with MyClassDto in order to call a service.
#PostMapping(
value="/sign",
consumes = { MediaType.APPLICATION_XML_VALUE, MediaType.APPLICATION_JSON_VALUE },
produces = { MediaType.APPLICATION_XML_VALUE, MediaType.APPLICATION_JSON_VALUE }
)
public MyClassRest prepareDocument(#RequestBody DocumentToPrepare documentToPrepare) throws Exception {
MyClassRest returnValue = new MyClassRest ();
ModelMapper modelMapper = new ModelMapper();
MyClassDto myClassDto = modelMapper.map(documentToPrepare, MyClassDto .class);
DocumentDto signedDocument = documentService.signDocument(documentDto);
returnValue = modelMapper.map(signedDocument, DocumentRest.class);
return returnValue;
}
My DTO class work fine and retrieve the OptionClass datas, but concerning the second Class, i obtain null as value, while i try to print it out in the service layer.

Answer 1

Your ConstantClass should be a Bean or a Component (as #cassiomolin says in comments)
#Component
public class ConstantClass {
private String hostName;
private String pathStart;
public ConstantClass (#Value("${api.url}") String url, #Value("${sign.path}") String path ) {
this.hostName = url;
this.pathStart = path;
}
// getters...
Then you can easily inject this component in your Controller and use it.
#Controller
public class YourController(){
private ConstantClass constantClass;
public YourController(ConstantClass constantClass){
this.constantClass = constantClass;
}
#PostMapping("...")
public MyClass post(.....){
.....
MyClass myclass = new MyClass(this.constantClass,...)
.....
}
}
note that Spring can autowire #Value and #Component, ... via the constructor; that can be very useful when you do unit-testing