Several solutions to implement initialization when Spring starts

To be precise, several initialization methods are completed after the instantiation of the spring container. Why do you say so?

Here is an example:

@Slf4j
@Component
public class InitBeanDemo {
    @Autowired
    private Environment env;

    public InitBeanDemo() {
        ("DefaultProfiles: {}", (()));
        ("ActiveProfiles: {}", (()));
    }

The example is to do some initialization work in the bean construction method. The example is relatively simple and only does log printing. It’s the ideal is full, the reality is skinny, and the error is reported:

Constructor threw exception; nested exception is

The reason is that Environment has not been initialized yet.

Next, let’s explore what initialization methods can meet the needs of the above example.

Initialization in the construction method

It can run normally and has the earliest execution time among all initialization methods.

The principle is to instantiate the Environment before InitBeanDemo is instantiated.

@Component
public class InitBeanDemo {

    private final Environment env;

    @Autowired
    public InitBeanDemo (Environment environment) {
         = environment;
        ("Constructor DefaultProfiles: {}", (()));
        ("Constructor ActiveProfiles: {}", (()));
    }
}

Regular three-piece set

Regular three-piece set: @PostConstruct, InitializingBean, initMethod.

If you prefer, the three ways can be used simultaneously under the same bean, priority of execution @PostConstruct > InitializingBean > initMethod.

@PostConstruct annotation

In a bean that can be scanned into, add a public void xxx() method and add @PostConstruct annotation to write the logic that needs to be initialized.

There can be multiple @PostConstruct annotations in the same application, and there can also be multiple @PostConstruct annotations in the same bean.

@Slf4j
@Component
public class InitBeanDemo {
    @Autowired
    private Environment env;

    @PostConstruct
    public void init() {
        ("@PostConstruct DefaultProfiles: {}", (()));
        ("@PostConstruct ActiveProfiles: {}", (()));
    }

Implement the InitializingBean interface

Implement the InitializingBean interface and write the logic that needs to be initialized in the afterPropertiesSet() method.

There can be multiple classes that implement the InitializingBean interface in the same application, and the execution opportunities are sorted in the natural order of the class names.

@Slf4j
@Component
public class InitBeanDemo implements InitializingBean {
    @Autowired
    private Environment env;

    @Override
    public void afterPropertiesSet() throws Exception {
        ("InitializingBean DefaultProfiles: {}", (()));
        ("InitializingBean ActiveProfiles: {}", (()));
    }
}

Specify the initMethod method of the bean

Use @Bean annotationinitMethodAttributes can be used for methods executed after initialization of a bean.

initMethod must be a parameterless constructor of public void.

@Slf4j
public class InitBeanDemo implements InitializingBean {
    @Autowired
    private Environment env;
    
	public void initMethod() {
        ("initMethod DefaultProfiles: {}", (()));
        ("initMethod ActiveProfiles: {}", (()));
    }

@Configuration
public class InitBeanConfig {

    @Bean(initMethod="initMethod")
    public InitBeanDemo initBeanDemo () {
        return new InitBeanDemo();
    }

}

Equivalent to the XML configurationinit-methodproperty:

<bean  class="" init-method="initMethod"></bean>

Custom ApplicationListener Listening

There are two ways, one implements the interface and the other uses annotations.

Implement the ApplicationListener interface

Listen to the ContextRefreshedEvent event.

@Slf4j
@Component
public class InitBeanDemo implements ApplicationListener<ContextRefreshedEvent>{
    @Autowired
    private Environment env;

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        ("ApplicationListener DefaultProfiles: {}", (()));
        ("ApplicationListener ActiveProfiles: {}", (()));
    }
}

@EventListener annotation

Specify the ContextRefreshedEvent event in the method parameter.

@Slf4j
@Component
public class InitBeanDemo {
    @Autowired
    private Environment env;

    @EventListener
    public void onApplicationEvent2(ContextRefreshedEvent event) {
        ("@EventListener DefaultProfiles: {}", (()));
        ("@EventListener ActiveProfiles: {}", (()));
    }
}

Initialization interface provided by Spring Boot

ApplicationRunner interface

@Slf4j
@Component
public class InitBeanDemo implements ApplicationRunner {
    @Autowired
    private Environment env;

    @Override
    public void run(ApplicationArguments args) throws Exception {
        ("ApplicationRunner: {}", args);
        ("ApplicationRunner: {}", ());
        ("ApplicationRunner DefaultProfiles: {}", (()));
        ("ApplicationRunner ActiveProfiles: {}", (()));
    }
}

CommandLineRunner interface

Multiple CommandLineRunner beans can be defined in the same application context and can be sorted using the @Ordered interface or the @Order annotation.

@Slf4j
@Component
public class InitBeanDemo implements CommandLineRunner {
    @Autowired
    private Environment env;

    @Override
    public void run(String... args) throws Exception {
        ("CommandLineRunner: {}", args);
        ("CommandLineRunner DefaultProfiles: {}", (()));
        ("CommandLineRunner ActiveProfiles: {}", (()));
    }
}

Use the above initialization method to execute order in the same bean

Use the above initialization method in the same bean to run the log fragment:

2021-06-07 11:24:41|INFO |main||Constructor DefaultProfiles: [default]
2021-06-07 11:24:41|INFO |main||Constructor ActiveProfiles: [sit]

2021-06-07 11:24:42|INFO |main||@PostConstruct DefaultProfiles: [default]
2021-06-07 11:24:42|INFO |main||@PostConstruct ActiveProfiles: [sit]
2021-06-07 11:24:42|INFO |main||InitializingBean DefaultProfiles: [default]
2021-06-07 11:24:42|INFO |main||InitializingBean ActiveProfiles: [sit]
2021-06-07 11:24:42|INFO |main||initMethod DefaultProfiles: [default]
2021-06-07 11:24:42|INFO |main||initMethod ActiveProfiles: [sit]

2021-06-07 11:24:44|INFO |main||@EventListener DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main||@EventListener ActiveProfiles: [sit]
2021-06-07 11:24:44|INFO |main||ApplicationListener DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main||ApplicationListener ActiveProfiles: [sit]

2021-06-07 11:24:44|INFO |main||ApplicationRunner: @68bef3df
2021-06-07 11:24:44|INFO |main||ApplicationRunner: []
2021-06-07 11:24:44|INFO |main||ApplicationRunner DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main||ApplicationRunner ActiveProfiles: [sit]

2021-06-07 11:24:44|INFO |main||CommandLineRunner: {}
2021-06-07 11:24:44|INFO |main||CommandLineRunner DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main||CommandLineRunner ActiveProfiles: [sit]

That is, the order of sorting out the entire article.

Summarize

The above is personal experience. I hope you can give you a reference and I hope you can support me more.