@Autowired field always null in subclasses

Question

I am trying to refactor my code that, among other things, returns a message depending on a parameter typeSignature.

The code below is the original working code (without the irrelevant parts) :

@Component
public class AuditUtil {
    @Autowired
    @Qualifier("messages")
    private ReloadableConfig conf;

    public Audit getTrace(int typeSignature, Order order) throws ParseException{
        Audit audit = new Audit();
        audit.setLabel(createMessage(typeSignature, order));
        return audit;
    }
    
    private String createMessage(int typeSignature, Order order) {
        List<Object> params = new ArrayList<>();
        params.add("canal");
        params.add(order.getId());
        if(typeSignature == 1){
            return MessageFormat.format(conf.getPropertyStr("message.simple.signature"), params.toArray());
        } else if(typeSignature == 2){
            return MessageFormat.format(conf.getPropertyStr("message.premiere.signature"), params.toArray());
        } else if(typeSignature == 3){
            return MessageFormat.format(conf.getPropertyStr("message.seconde.signature"), params.toArray());
        }
    }
}

I wanted to try the command pattern, so I did that (I'll show only 1 concrete subclass of SignatureMessageBuilder):

@Component
public class AuditUtil {
    static Map<Integer, SignatureMessageBuilder> signatureCommandMap;
    static {
        signatureCommandMap = new HashMap<>();
        signatureCommandMap.put(1, new SimpleSignatureMessageBuilder());
        signatureCommandMap.put(2, new FirstSignatureMessageBuilder());
        signatureCommandMap.put(3, new SecondSignatureMessageBuilder());
    }
    
    @Autowired
    @Qualifier("messages")
    private ReloadableConfig conf;

    public Audit getTrace(int typeSignature, Order order) throws ParseException{
        Audit audit = new Audit();
        audit.setLabel(createMessage(typeSignature, order));
        return audit;
    }
    
    private String createMessage(int typeSignature, Order order) {
        List<Object> params = new ArrayList<>();
        params.add("canal");
        params.add(order.getId());
        return signatureCommandMap.containsKey(typeSignature) ? signatureCommandMap.get(typeSignature).buildMessage() : "";
    }
}

public abstract class SignatureMessageBuilder {
    protected ReloadableConfig conf;
    
    @Autowired
    public final void setConfig(@Qualifier("messages") ReloadableConfig conf) {
        this.conf = conf;
    }

    public abstract String buildMessage();

    // ommitted common protected methods for subclasses
}


@Component
public class SimpleSignatureMessageBuilder extends SignatureMessageBuilder {
    private String template;

    @Override
    public String buildMessage() {
        template = conf.getPropertyStr("message.simple.signature");
        return template;
    }
}

It doesn't work : I get a NullPointerException in the SimpleSignatureMessageBuilder.buildMessage() because conf is null.

I've also tried to put the signatureCommandMap initialization in a AuditUtil constructor, conf is still null.

What am I doing wrong ?