How to inject dependencies into a self-instantiated object in Spring?

Question

Let's say we have a class:

public class MyClass {
    @Autowired private AnotherBean anotherBean;
}

Then we created an object of this class (or some other framework have created the instance of this class).

MyClass obj = new MyClass();

Is it possible to still inject the dependencies? Something like:

applicationContext.injectDependencies(obj);

(I think Google Guice has something like this)

Tamatamable

Answer 1

You can do this using the autowireBean() method of AutowireCapableBeanFactory. You pass it an arbitrary object, and Spring will treat it like something it created itself, and will apply the various autowiring bits and pieces.

To get hold of the AutowireCapableBeanFactory, just autowire that:

private @Autowired AutowireCapableBeanFactory beanFactory;

public void doStuff() {
   MyBean obj = new MyBean();
   beanFactory.autowireBean(obj);
   // obj will now have its dependencies autowired.
}

Phallicism

Good answer (+1). There's also a second method where you can influence how the autowiring happens: static.springsource.org/spring/docs/3.0.x/javadoc-api/org/… – Bugbear

But what if I have two objects, and first autowires second. How autowire bean factory deals with dependencies in the case? – Gordongordy

This is actually a bad pattern. If this is how you really use MyBean why not just have constructor with AnotherBean as parameter. Something like: code private @Autowired AnotherBean bean; public void doStuff() { MyBean obj = new MyBean(bean); } code. Seems to be like with all these annotations people get really confused and just don't use the basic pattern that were in java SDK since day 1. :( – Ungovernable

I agree - Spring has redefined the entire language. Now we use interfaces as concrete classes, methods as class instances and all manner of complicated and code heavy methods of doing what you used to do with new and a decent design. – Sherrylsherurd

@Ungovernable if MyBean has dependencies that the actual class don't need, you're registering dependencies that doesn't actually exist, just to instance a class, so there's really no difference. – Dogeatdog

I think the answer by @glaz666 is much cleaner/better than this. The only disadvantage of using @Configurable I can see is that it requires Spring to use AspectJ under the covers. – Kaleykaleyard

It is a very useful capability and the answer is quite correct. Some frameworks , like struts 2, use this feature to autowire their beans. See #39706721 – Chalone

actually there has nothing mentioned about this in spring framework reference documentation, why is that – Attic

There is also another very helpful BeanFactory method that does NOT autowire the bean as such (i.e. it does not inject dependencies by means of setter or field injection), but it does make the bean aware of its surroundings by injecting application context, reference to a bean factory, invoking post-initialization callbacks, and assigning bean a name. And it does not require a BeanDefinition to be present (something that autowire() method expects): initializeBean(Object existingBean, String beanName) – Rexer

Answer 2

You can also mark your MyClass with @Configurable annotation:

@Configurable
public class MyClass {
   @Autowired private AnotherClass instance
}

Then at creation time it will automatically inject its dependencies. You also should have <context:spring-configured/> in your application context xml.

Specific

Galz666, your method looks much cleaner for what I want to do. However I cannot get it to work. I have no xml file and am using entirely Java config. Is there an equivalent to <context:spring-configured/> ? – Askew

This is clean solution, but requires a little more effort: You should either use load-time weaving as iimuhin shows above or add AspectJ compiler to project. Load-time as the name suggest will cause additional cost at run-time. – Allaround

Answer 3

Just got the same need and in my case it was already the logic inside non Spring manageable java class which had access to ApplicationContext. Inspired by scaffman. Solved by:

AutowireCapableBeanFactory factory = applicationContext.getAutowireCapableBeanFactory();
factory.autowireBean(manuallyCreatedInstance);

Dorman

Answer 4

I used a different approach. I had spring loaded beans that I wanted to call from my extended classes of a third-party library that created its own threads.

I used approach I found here https://confluence.jaytaala.com/display/TKB/Super+simple+approach+to+accessing+Spring+beans+from+non-Spring+managed+classes+and+POJOs

In the non-managed class:

{
    [...]
    SomeBean bc = (SomeBean) SpringContext.getBean(SomeBean.class);

    [...]
    bc.someMethod(...)
}

And then as a helper class in the main application:

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class SpringContext implements ApplicationContextAware
{
    private static ApplicationContext context;

    public static <T extends Object> T getBean(Class<T> beanClass)
    {   
        return context.getBean(beanClass);
    }

    @Override
    public void setApplicationContext(ApplicationContext context) throws BeansException
    {   
        SpringContext.context = context;
    }
}

Loisloise

This worked for me after going to the confluence link. Have upvoted it. – Jacquie

This work for me thanks. If you are in my country. i am glad to treat you beer – Sullen

Answer 5

I wanted to share my solution that follows the @Configurable approach as briefly mentioned in @glaz666 answer because

• The answer by @skaffman is nearly 10 years old, and that does not mean not good enough or does not work
• The answer by @glaz666 is brief and didn't really help me solve my problem but, did point me in the right direction

My setup

1. Spring Boot 2.0.3 with Spring Neo4j & Aop starts (which is irrelevant anyway)
2. Instantiate a bean when Spring Boot is ready using @Configurable approach (using ApplicationRunner)
3. Gradle & Eclipse

Steps

I needed to follow the steps below in order to get it working

1. The @Configurable(preConstruction = true, autowire = Autowire.BY_TYPE, dependencyCheck = false) to be placed on top of your Bean that is to be manually instantiated. In my case the Bean that is to be manually instantiated have @Autowired services hence, the props to above annotation.
2. Annotate the Spring Boot's main XXXApplicaiton.java (or the file that is annotated with @SpringBootApplication) with the @EnableSpringConfigured and @EnableLoadTimeWeaving(aspectjWeaving=AspectJWeaving.ENABLED)
3. Add the dependencies in your build file (i.e. build.gradle or pom.xml depending on which one you use) compile('org.springframework.boot:spring-boot-starter-aop') and compile('org.springframework:spring-aspects:5.0.7.RELEASE')
4. New+up your Bean that is annotated with @Configurable anywhere and its dependencies should be autowired.

*In regards to point #3 above, I am aware that the org.springframework.boot:spring-boot-starter-aop transitively pulls the spring-aop (as shown here mavencentral) but, in my case the Eclipse failed to resolve the @EnableSpringConfigured annotations hence, why I explicitly added the spring-aop dependency in addition to the starter. Should you face the same issue, just declare the dependency or go on adventure of figuring out

• Is there a version conflict
• Why the org.springframework.context.annotation.aspect.* is not available
• Is your IDE setup properly
• Etc etc.

Antiseptic

Answer 6

This worked for me:

@Configuration
public class AppConfig {
    @Bean
    public TransferService transferService() {
        return new TransferServiceImpl();
    }
}

See more information: https://docs.spring.io/spring-javaconfig/docs/1.0.0.m3/reference/html/creating-bean-definitions.html

Candlestick

Answer 7

Found the following way useful for my use case. Sharing here for reference, credit goes to the blogger entirely. This creates a static field and populates that from Spring and then provides a public static method which returns the field populated above.

https://sultanov.dev/blog/access-spring-beans-from-unmanaged-objects/

Auriol