Is it possible to @Lazy init a Spring @Value?

Question

Is it possible to @Lazy init a Spring @Value?

e.g.

@Lazy
@Value("${someConfig}")
private String someConfig;

The scenario I'm specifically referring to, is a variable which is set via JNDI, and an embedded Tomcat container, which has some of it's JNDI variables initialised during Spring Boot loading... other scenarios I could think of where you'd want JIT variable population: It's "expensive" to retrieve a variable and you don't want to impact startup time, the variable isn't available at application startup, etc.

The above code gives the following error:

java.lang.IllegalArgumentException: Cannot subclass final class java.lang.String

I imagine you could possibly achieve lazy-loaded variables by using a @ConfigurationProperties bean?

A follow up question: Can/Would a @Value-initialised variable be reinitialised (without an app restart), if the underlying variable source is changed (e.g. JNDI on the server)? i.e. re-retrieved

(I'm in the process of trying these last two scenarios)

No, to your follow up question, not for a field in a singleton bean. But if you managed to declare the bean as singleton and get a new instance each time, that field would get initialized to the current value each time. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented May 4, 2016 at 23:52
As a note on the specific error: @Lazy is implemented by replacing the field with a proxy, which can't be done if the field's declared type is a final class. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented May 5, 2016 at 0:02

Maciej Walkowiak · Accepted Answer · 2016-11-07 23:58:10Z

7

+50

You can give a try to such a setup. Downside is that it requires beans using this variable to be also declared as @Lazy.

@Bean(name = "myVar")
@Lazy
String foo(@Value("${someConfig}") String someConfig) {
    return someConfig;
}

@Component
@Lazy
class SomeComponent {

    @Autowired
    @Qualifier("myVar")
    String myVar;
}

answered Nov 7, 2016 at 23:58

Maciej Walkowiak

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