与Spring Batch阅读器结合使用时无法调用@PostConstruct

Question

I've been trying to implement @PostConstruct and @PreDestroy methods in an Account class of mine. Neither of them worked in the following situation, but for the sake of brevity, I'll only talk about @PostConstruct .

I'm using Spring Batch's readers to load these accounts from a fixed-length file. So far, so good, except when my reader creates these accounts, it apparently does not call the @PostConstruct method (debug breakpoints are never activated, and log messages are not printed out).
The reader is only custom in the sense that it's a custom class extending FlatFileItemReader<Account> and setting values in the constructor.

Adding the exact same initialization method (that never got called in the Account class) to the reader itself works just fine.
Ie if the @PostConstruct method should be called upon reader initialization, it works. Just not when the reader itself initializes accounts annotated with @PostConstruct .

If I add a breakpoint or log message in the constructor of Account directly, it also works without an issue.

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Is this desired behaviour by Spring Batch? Or could this be caused by any configuration of mine?

Another question's answer mentioned that annotations such as @PostConstruct "only apply to container-managed beans", not if "you are simply calling new BlogEntryDao() yourself".

Is this what's happening here - Spring Batch calling new Account(...) directly, without registering them in the container? After all, I never have these accounts available as beans or anything.

Answer 1

Is your Account class annotated with @Component , @Bean or @Service ? If you create objects of account class like Account c = new Account() the nSpring doesn't know about creation of such objects. Because of that Spring doesn't call method annotated with @postConstruct

Answer 2

when my reader creates these accounts, it apparently does not call the @PostConstruct method

@PostConstruct and @PreDestroy methods are called by the Spring container after creating and before destroying the instance of your bean. If your object is not managed by Spring, those methods will not be called.

I'm using Spring Batch's readers to load these accounts from a fixed-length file

In this case, you should have already configured a FieldSetMapper to map fields to an Account instance. If you use the BeanWrapperFieldSetMapper , you can set the PrototypeBeanName which is the name of a bean (for example of type Account ) of scope prototype (so that an instance is created for each line). This way, Account instances will be managed by Spring, used by Spring Batch reader, and your method annotated with PostConstruct will be called. Here is an example:

@Bean
@Scope("prototype")
public Account account() {
    return new Account();
}

@Bean
public BeanWrapperFieldSetMapper<Account> beanMapper() {
    BeanWrapperFieldSetMapper<Account> fieldSetMapper = new BeanWrapperFieldSetMapper<>();
    fieldSetMapper.setPrototypeBeanName("account");
    return fieldSetMapper;
}

@Bean
public FlatFileItemReader<Account> accountReader() {
    return new FlatFileItemReaderBuilder<Account>()
            .name("accountsItemReader")
            .resource(new ClassPathResource("accounts.txt"))
            .fixedLength()
            .columns(new Range[] {new Range(1, 1), new Range(2, 4)})
            .names(new String[]{"id", "name"})
            .fieldSetMapper(beanMapper())
            .build();
}

More details about this in the Javadoc .

Hope this helps.