当使用自动接线时，将是示例的受益者

Question

I have recently learned concept of autowiring in spring. When I was trying to understand in which particular scenarios spring autowiring can be useful I came up with the below two reasons from one of the questions asked in our stakoverflow forum.

1.I wanted to read values from a property file and inject them into a bean. Only way I could figure out how to do this at start up of my app was to wire the bean in XML (and inject the properties.) I ended up using the "byName" attribute (because the bean was also marked as @Component ) and then used @Autowired @Qualifier("nameIChose") when injecting the bean into another class. It's the only bean I've written that I wire with XML.

2.I've found autowiring useful in cases where I've had a factory bean making another bean (whose implementation class name was described in a system property,so I couldn't define the all wiring in XML). I usually prefer to make my wiring explicit though;

Can any body please give me some code snippet example of the above situations that would make my understanding of autowiring more clearer?

Answer 1

Here is an example of injecting properties into a bean.

Using field injection:

@Component
public class YourBean {

    @Value("${your.property.name}")
    private String yourProperty;
}

Using constructor injection:

@Component
public class YourBean2 {

    private String yourProperty;

    @Autowired
    public YourBeans2(@Value("${your.property.name}") String yourProperty) {
       this.yourProperty = yourProperty;
    }
}

The following is a super simple example of autowiring various beans

@Component
public class Foo {

    public void doSomething() {

    }
}

@Component
public class Bar {

   private Foo foo;

   @Autowired
   public Bar(Foo foo) {
      this.foo = foo;
   }

   public void doSomethingElse() {
      foo.doSomething();
   }
}

In the previous example, no XML configuration of Foo and Bar needs to be done, Spring automatically picks up the beans because of their @Component annotation (assuming of course that component scanning has been enabled)