Spring - register scoped bean at runtime

Question

I am working on a Spring-based application which registers a custom scope "task". The idea is that when a new Task is started, Spring should supply task-scoped objects.

The task is instantiated in the runtime. It is supplied with some configuration in the form of a Properties object. I want to register that object with the ApplicationContext but within the task scope so that all beans within that scope can reference the configuration of that particular task.

Here is the rough idea in code:

public class MyTask extends SourceTask {
    @Override
    public void start(Map<String, String> props) {
        context = ContextProvider.getApplicationContext();
        // Initialize the scope
        ConnectorTaskScope scope = context.getBean(ConnectorTaskScope.class);
        scope.startNewTask();

        // TODO register the props object in the context

        // get an object which requires the properties and work with it
        context.getBean(SomeScopedBean.class);        
    }
}

I can't figure out how can I register a bean in the ApplicationContext that is scoped appropriately.

Thank you

Update:

Here is some more code to explain the question a bit better. SomeScopedBean should be doing something with the configuration it has bean provided with and looks something like this:

public class SomeScopedBean {
    @Autowire
    public SomeScopedBean (Properties configuration) {
        // do some work with the configuration 
    }
}

The idea of the application is that it should have multiple instances of MyTask running with different configuration and each task is its own scope. Within the scope of each task, there should be 1 instance of SomeScopedBean initialized with the task's configuration.

public class MyApplication {
    public static void main (String[] args) {
        // ...
        Properties config1 = loadConfiguration1();
        Properties config2 = loadConfiguration2();
        MyTask task1 = new MyTask();
        MyTask task2 = new MyTask();
        task1.start(config1);
        task2.start(config2);
        // ...
    }
}

http://memorynotfound.com/spring-custom-scope-creating-and-implementing-threadscope/ — StanislavL, Apr 12 '17 at 09:32
@StanislavL, I've got the custom scope implemented and it works fine. The question is how to register a scoped bean at runtime. — artemb, Apr 12 '17 at 09:53
Have you tried using `scope=prototype` which creates a new instance of the class wherever it is injected? — Downhillski, Apr 16 '17 at 21:03
See [this question](http://stackoverflow.com/questions/28374000/spring-programmatically-generate-a-set-of-beans) about registering Spring beans dinamically — fps, Apr 16 '17 at 21:20
@ZhenyangHua, I am not sure how this would help me. `SomeScopedBean` should be autowired with the configuration which is specific to the current scope. — artemb, Apr 17 '17 at 10:32
Im not an expert but this approach seems a bit off. Scopes are used to separate bean instances but it looks like what you want is to separate bean definitions. Usual workflow is: create bean definition and let scope decide whether create a new instance or use existing one. — chimmi, Apr 17 '17 at 13:35
Have you tried wire your `SomeScopedBeans` class manually by using prototype scope? this way gets more flexibility with scoping for instance and prototype. — Downhillski, Apr 17 '17 at 14:02
`The question is how to register a scoped bean at runtime.` In your example, which scoped bean do you want to register ?. If you take the @StanislavL links, you can inject `ThreadScope`, add a method `register(Bean)`, and call it inside your thread — Nicolas Labrot, Apr 20 '17 at 20:15
@chimmi, maybe scopes are not the best tool for this. What I want is to have 1 instance of `SomeScopedBean` within each scope (within each `MyTask`), but each configured with different configuration properties (which are provided by the deployment framework when it instantiates each Task, so I have no control of it). Maybe there is a better way to do that, I just don't know. — artemb, Apr 23 '17 at 15:03

Nicolas Labrot · Accepted Answer · 2017-04-24T08:55:30.750

If I take your last comment:

What I want is to have 1 instance of SomeScopedBean within each scope (within each MyTask), but each configured with different configuration properties (which are provided by the deployment framework when it instantiates each Task,

And especially within each MyTask and if it is limited to MyTask.

You can:

define SomeScopedBean as a prototype bean
create a factory @Configuration which will instantiate SomeScopedBean with the provided properties configuration

First the configuration:

@Configuration
public class SomeScopedBeanFactoryConfiguration {

    @Bean
    @Scope(BeanDefinition.SCOPE_PROTOTYPE)
    public SomeScopedBean create(Properties configuration) {
        return new SomeScopedBean(configuration);
    }

}

Then autowired the SomeScopedBeanFactoryConfiguration into MyTask and creates SomeScopedBean:

public class MyTask extends SourceTask {

    @Autowired
    private SomeScopedBeanFactoryConfiguration  someScopedBeanFactoryConfiguration;

    @Override
    public void start(Map<String, String> props) {
        SomeScopedBean scopedBean = someScopedBeanFactoryConfiguration.create(props);    
    }
}

Note: if SomeScopedBean must be injected in more than one bean with the task/thread scope, you could change its scope to your thread scope one eg.:

    @Bean
    @Scope("thread")
    public SomeScopedBean create(Properties configuration) {
        return new SomeScopedBean(configuration);
    }

This looks promising. I wonder if other beans within the same ("task") scope then can require SomeScopedBean and be provided with the correctly-configured instance. I will try that — artemb, Apr 24 '17 at 08:45
It should if you set the scope of `SomeScopedBean` to your `task` scope and not the `prototype` one — Nicolas Labrot, Apr 24 '17 at 08:56
Yes! That worked exactly how I wanted it to! A but non-intuitive to set it up, but works as I wanted it to! Thank you — artemb, Apr 24 '17 at 09:47

StanislavL · Answer 2 · 2017-04-24T08:58:35.727

AutowireCapableBeanFactory beanFactory = applicationContext.getAutowireCapableBeanFactory();

MyTask instance = new MyTask();
beanFactory.autowireBean(instance);
beanFactory.initializeBean(instance, MyTask.class.getCanonicalName());

//for singleton I used
((ConfigurableListableBeanFactory)beanFactory).registerSingleton(MyTask.class.getCanonicalName(), instance);

In your case I would register singleton of MyTask Proxy. The Proxy can keep all your scope dependent instances (e.g. in a Map or in ThreadLocal storage) and on call delegate logic to correct one from the Map.

UPDATE: Actually you autowire not MyTask bean but a Proxy. The proxy wraps all the MyTask methods. Proxy has the same interface as MyTask. Suppose you call ProxyMyTask.do() method. The proxy intercepts the call, get somehow scope e.g. current thread in case of Tread Scope example and get from the Map (or for Thread Scope from ThreadLocal storage) proper instance of MyTask. Finally calls the do(0 method of the found MyTask instance.

UPDATE 2: See the example http://tutorials.jenkov.com/java-reflection/dynamic-proxies.html You can easily wrap an interface. Your logic to determine scope and return proper instance should be in the method

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    return method.invoke(target, args);
}

Ok, so if MyTask stores all scope-dependent instances in a map, when MyTask method is called, how will it know within which scope it has been called? — artemb, Apr 23 '17 at 14:59
Thank you! In this case MyTaskProxy - is this something that I develop or is it provided by Spring? — artemb, Apr 24 '17 at 08:46

Spring - register scoped bean at runtime

2 Answers2