What happens first at startup of a Spring boot application - loading of the application.properties file or creations of beans annotated with @Bean?

I've this class:

@Slf4j
@Configuration
public class TxnIdGeneratorProperties {

    @Bean
    public TimeBasedTxnIdGenerator seqGenerator() {
        if (log.isInfoEnabled())
            log.info("{} Loading CustomProperties :: getTxnIdGeneratorAccounts....", BOOT_CONFIG);

        TimeBasedTxnIdGenerator sequencer = new TimeBasedTxnIdGenerator();
        sequencer.calculateLimit();
        return sequencer;
    }

}

Here I'm creating an object of TimeBasedTxnIdGenerator, calling the calculateLimit() method, and returning the same object as the bean that must be created during startup. This is the TimeBasedTxnIdGenerator class:

@Service
public class TimeBasedTxnIdGenerator extends AbstractSequencer implements TransactionIdGenerator {
    
    @Value("${qr.code.app.url}")
    private String qrCodeAppUrl;
    
    private static final int NODE_ID_BITS = 10;
    private static final long maxNodeId = (1L << NODE_ID_BITS) - 1;

    public TimeBasedTxnIdGenerator() {
        super();
    }
    
    @Override
    public synchronized String doExecute() {
        return getSequenceId();
    }
    
    private static long createNodeId() {
        long nodeId;
        try {
            StringBuilder sb = new StringBuilder();
            Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();
            while (networkInterfaces.hasMoreElements()) {
                NetworkInterface networkInterface = networkInterfaces.nextElement();
                byte[] mac = networkInterface.getHardwareAddress();
                if (mac != null) {
                    for(byte macPort: mac) {
                        sb.append(String.format("%02X", macPort));
                    }
                }
            }
            nodeId = sb.toString().hashCode();
        } catch (Exception ex) {
            nodeId = (new SecureRandom().nextInt());
        }
        nodeId = nodeId & maxNodeId;
        return nodeId;
    }

    @Override
    public void calculateLimit() {
        
        System.out.println("MFS App param : " + qrCodeAppUrl);
        
        long nodeId = createNodeId();
        setSequencerLimit(nodeId);
    }   
}

The problem is when I try to read this qr.code.app.url configuration value from the application.properties file, when I print the value at the startup, it is getting printed as null. But when I change the data type of qrCodeAppUrl from String to int, I'm getting this startup error:

Caused by: org.springframework.beans.TypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'int'; For input string: "digipay://pay?"

So, the application knows the value of that configuration before calling the calculateLimit() method, but inside the method, its value is printed as null. Why is that?

You're creating the class instance with new, the @Value annotation on the field is not going to get evaluated. EDIT: as pointed out by @SotiriosDelimanolis in the comment, the annotation is going to get evaluated, but only after the object is returned from the method.

You can create Beans either with the @Service annotation or in the @Configuration as a @Bean. To inject the value that way, you can do

public class TimeBasedTxnIdGenerator extends AbstractSequencer implements TransactionIdGenerator {
    private final String qrUrl;

    public TimeBasedTxnIdGenerator(String url) {
        qrUrl = url;
    }
    // ...
}

@Configuration
public class Config {
    @Bean
    public TimeBasedTxnIdGenerator seqGenerator(@Value("${qr.code.app.url}") String qrCodeAppUrl) {
        if (log.isInfoEnabled())
            log.info("{} Loading CustomProperties :: getTxnIdGeneratorAccounts....", BOOT_CONFIG);

        TimeBasedTxnIdGenerator sequencer = new TimeBasedTxnIdGenerator(qrCodeAppUrl);
        sequencer.calculateLimit();
        return sequencer;
    }
}