XML 定义的 spring bean 的程序等价物是什么

Question

What is the programatic equivalane to defining a bean like this in xml:

<bean id="foo" class="com.bizz.Foo" />

Ideally I would like to be able to have spring create that bean, without using XML and without calling new and for this to happen within a @Configuration type class. For example:

@Configuration
public ConfigBar {
  @Bean
  public com.bizz.Foo foo() {
    return /* Programmatic equivalent of <bean id="foo" class="com.bizz.Foo" /> here*/; 
  }
}

I don't think new Foo() is equivalent:

• as spring is able to pick which constructor to use which may not be the no args constructor.
• and spring is able to inject dependencies, which I don't think will be done here.

I know that spring is doing some reflection to achieve this, however simply stating that is not the answer to this question.

so how can we let spring create the Foo bean programmatically letting spring inject dependencies, pick the constructor and perhaps other tasks that spring would normally do when defined in XML?

Answer 1

The equivalent is @Component or any variant thereof such as @Controller or @Service . So long as your bean is in a package included in the component scan Spring will be able to find your bean at runtime and inject it into other beans.

As an example:

@Component
public class Foo {
    //...
}

@Service
public class Bar {

    // Spring will find and inject Foo bean creating it if necessary when 
    // creating the Bar "service" bean 
    @Autowired
    private Foo foo;

    //...
}

Answer 2

I have worked it out:

@Bean
@Autowired
public Foo foo(AutowireCapableBeanFactory autowireCapableBeanFactory) {
    return autowireCapableBeanFactory.createBean(Foo.class);
}