How to instantiate spring managed beans at runtime?

Question

I stuck with a simple refactoring from plain java to spring. Application has a "Container" object which instantiates its parts at runtime. Let me explain with the code:

public class Container {
    private List<RuntimeBean> runtimeBeans = new ArrayList<RuntimeBean>();

    public void load() {
        // repeated several times depending on external data/environment
        RuntimeBean beanRuntime = createRuntimeBean();
        runtimeBeans.add(beanRuntime);
    }

    public RuntimeBean createRuntimeBean() {
         // should create bean which internally can have some 
         // spring annotations or in other words
         // should be managed by spring
    }
}

Basically, during load container asks some external system to provide him information about number and configuration of each RuntimeBean and then it create beans according to given spec.

The problem is: usually when we do in spring

ApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfiguration.class);
Container container = (Container) context.getBean("container");

our object is fully configured and have all dependencies injected. But in my case I have to instantiate some objects which also needs dependency injection after I execute load() method. How can I achieve that?

I am using java-based config. I already tried making a factory for RuntimeBeans:

public class BeanRuntimeFactory {

    @Bean
    public RuntimeBean createRuntimeBean() {
        return new RuntimeBean();
    }
}

expecting @Bean to work in so called 'lite' mode. http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/annotation/Bean.html Unfortunately, I found no difference with simply doing new RuntimeBean(); Here is a post with a similar issue: How to get beans created by FactoryBean spring managed?

There is also http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/beans/factory/annotation/Configurable.html but it looks like a hammer in my case.

I also tried ApplicationContext.getBean("runtimeBean", args) where runtimeBean has a "Prototype" scope, but getBean is an awful solution.

Upd1. To be more concrete I am trying to refactor this class: https://github.com/apache/lucene-solr/blob/trunk/solr/core/src/java/org/apache/solr/core/CoreContainer.java @see #load() method and find "return create(cd, false);"

Upd2. I found quite interesting thing called "lookup method injection" in spring documentation: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html#beans-factory-lookup-method-injection

And also an interesting jira ticket https://jira.spring.io/browse/SPR-5192 where Phil Webb says https://jira.spring.io/browse/SPR-5192?focusedCommentId=86051&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-86051 that javax.inject.Provider should be used here (it reminds me Guice).

Upd3. There is also http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/beans/factory/config/ServiceLocatorFactoryBean.html

Upd4. The issue with all these 'lookup' methods is they don't support passing any arguments.. I also need to pass arguments as I would do with applicationContext.getBean("runtimeBean", arg1, arg2). Looks like it was fixed at some point with https://jira.spring.io/browse/SPR-7431

Upd5. Google Guice have a neat feature for it called AssistedInject. https://github.com/google/guice/wiki/AssistedInject

Answer 1

Looks like I found a solution. As I am using java based configuration it is even simpler than you can imagine. Alternative way in xml would be lookup-method, however only from spring version 4.1.X as it supports passing arguments to the method.

Here is a complete working example:

public class Container {
    private List<RuntimeBean> runtimeBeans = new ArrayList<RuntimeBean>();
    private RuntimeBeanFactory runtimeBeanFactory;

    public void load() {
        // repeated several times depending on external data/environment
        runtimeBeans.add(createRuntimeBean("Some external info1"));
        runtimeBeans.add(createRuntimeBean("Some external info2"));
    }

    public RuntimeBean createRuntimeBean(String info) {
         // should create bean which internally can have some 
         // spring annotations or in other words
         // should be managed by spring
         return runtimeBeanFactory.createRuntimeBean(info)
    }

    public void setRuntimeBeanFactory(RuntimeBeanFactory runtimeBeanFactory) {
        this.runtimeBeanFactory = runtimeBeanFactory
    }
}

public interface RuntimeBeanFactory {
    RuntimeBean createRuntimeBean(String info);
}

//and finally
@Configuration
public class ApplicationConfiguration {

    @Bean
    Container container() {
        Container container = new Container(beanToInject());
        container.setBeanRuntimeFactory(runtimeBeanFactory());
        return container;
    }

    // LOOK HOW IT IS SIMPLE IN THE JAVA CONFIGURATION
    @Bean 
    public BeanRuntimeFactory runtimeBeanFactory() {
        return new BeanRuntimeFactory() {
            public RuntimeBean createRuntimeBean(String beanName) {
                return runtimeBean(beanName);
            }
        };
    }

    @Bean
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    RuntimeBean runtimeBean(String beanName) {
        return new RuntimeBean(beanName);
    }
}

class RuntimeBean {
    @Autowired
    Container container;
}

That's it.

Thanks everyone.