Dependency injection without using spring framework

Question

I have a rather naive question. Can we inject dependencies using core java just like how we inject using Spring framework?

For now, I do something like this:

In web.xml:

<context-param>
     <param-name>contextConfigLocation</param-name>
     <param-value>classpath:applicationContext.xml</param-value>
</context-param>
<listener>
     <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

spring applicationcontext.xml:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans.xsd
  http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context.xsd">

    <bean id="mybean" class="com.test.app.MyService" />

</beans>

Class where I will use the injected bean:

public class MyResource {

    @Autowired
    private MyService mybean;

     public MyResponse doService(MyRequest req) {
           mybean.doBusiness(req);
     }
}

}

So, is there a way we can do this dependency injection using core java? I have been reading a bit on CDI but didn't understand it well. Plus, it also felt like it was not a direct substitution of what Spring does.

Please help and correct me if I am wrong.

Answer 1

javax.inject (JSR-330) and CDI (JSR-299, JSR-346) are just APIs, not implementations. There are implementations of these APIs that do work in Java SE (as opposed to Java EE, which I suppose is what you mean by "core Java"), e.g. Weld SE.

CDI builds upon JSR-330.

While javax.inject is only about basic injection and does not address scopes and lifecycles, it is fair to say that CDI and Spring Core are more or less equally powerful. Both can be used in Java SE.

Answer 2

@Autowired is a Spring annotation that is not standardized. The corresponding standard annotation is @Inject from javax.inject

Aside from Spring, Google Guice supports also javax.inject

Another extremely lightweight framework for dependency injection (that does not support javax.inject) is PicoContainer