How to Inject Dependencies into Self-Instantiated Objects in Spring?

Overcoming Injection Challenges for Self-Instantiated Objects in Spring

When working with Spring, it is common to manage dependencies through annotations and dependency injection. However, situations may arise where you have a self-instantiated object outside of the Spring context. In such cases, how can you still leverage Spring's injection capabilities?

The Dilemma: Manual Instantiation and Dependency Management

Consider the following scenario:

<code class="java">public class MyClass {
    @Autowired private AnotherBean anotherBean;
}

...

MyClass obj = new MyClass();</code>

You have instantiated MyClass manually but want to inject its dependencies like anotherBean. How do you go about it?

Solution: Utilizing the AutowireCapableBeanFactory

Spring provides the AutowireCapableBeanFactory interface, which enables us to inject dependencies into any arbitrary object, including self-instantiated ones. To access the BeanFactory:

<code class="java">private @Autowired AutowireCapableBeanFactory beanFactory;</code>

Injecting Dependencies into a Self-Instantiated Object

Using the beanFactory, you can inject dependencies into your object:

<code class="java">public void doStuff() {
   MyBean obj = new MyBean();
   beanFactory.autowireBean(obj);
   // obj will now have its dependencies autowired.
}</code>

After calling autowireBean, your instantiated object will have its dependencies injected and ready for use. This approach allows you to leverage Spring's dependency injection capabilities even for objects you create manually.

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