Why use @PostConstruct?

Question

In a managed bean, @PostConstruct is called after the regular Java object constructor.

Why would I use @PostConstruct to initialize by bean

Answer 1

The main problem is that:

in a constructor, the injection of the dependencies has not yet occurred*

_{*obviously excluding Constructor Injection}

---

Real-world example:

public class Foo {

    @Inject
    Logger LOG;

    @PostConstruct
    public void fooInit(){
        LOG.info("This will be printed; LOG has already been injected");
    }

    public Foo() {
        LOG.info("This will NOT be printed, LOG is still null");
        // NullPointerException will be thrown here
    }
}

---

IMPORTANT: @PostConstruct and @PreDestroy have been completely removed in Java 11.

To keep using them, you'll need to add the javax.annotation-api JAR to your dependencies.

Maven

    javax.annotation
    javax.annotation-api
    1.3.2

Gradle

// https://mvnrepository.com/artifact/javax.annotation/javax.annotation-api
compile group: 'javax.annotation', name: 'javax.annotation-api', version: '1.3.2'