Java spring @Value注释

Question

I have a Spring Boot application with a class TokenProvider where i get some token from application.properties. In another controller class TestController i need to create a object new TokenProvider and retrieve the value. It gives me null values. Why it doesn't work ?

PS: If i inject TokenProvider in TestController (with @Autowired JwtTokenProvider tokenProvider; )it works.

Why i cannot retrieve token without injecting ?

@Component
public class JwtTokenProvider {
    private static Logger logger = LoggerFactory.getLogger(JwtTokenProvider.class);

    @Value("${app.jwtSecret}")
    private String jwtSecret;

    public String getJwtSecret() {
        return jwtSecret;
    }

}

@RestController
@RequestMapping("/test")
public class TestController {

//    @Autowired
//    JwtTokenProvider tokenProvider;

    @RequestMapping(value = "/get_propertie")
    public String getPropertie() {
        JwtTokenProvider jwt = new JwtTokenProvider();
        String res = "jwt" + jwt.getJwtSecret();
        return res;
    }
}

Answer 1

in case of creating JwtTokenProvider with new it is not being created by Spring and all annotations like @Value are basically being ignored - that's how Spring is working. What you can do is to create the JwtTokenProvider in proper Java @Configuration class providing @Value String token parameter

@Configuration
public class TokenConfig {
    @Bean
    public JwtTokenProvider jwtTokenProvider(@Value("${app.jwtSecret}") token) {
        return new JwtTokenProvider(token); // or some setter depends on what the class provide
    }
}

but still - you need to use on of Spring dependency injection mechanism to have @Value working

Answer 2

See https://baledung.com/spring-value-annotation

You can use the @Value annotation to inject values into fields in beans that Spring manages.

If your bean is not @Autowired, Spring can't inject the value.

In case you don't want to use the @Value annotation, you can always use the Java Properties class (with .getProperty method) to retrieve your value.