injection and lookup

[Raj chiru]

hi..
Any explain to me what is difference between injection and lookup?

[kurt hanni]

Dependency Lookup is when your class is responsible for getting its dependencies from some lookup factory, (this is similar to a JNDI lookup).
for example ClassA has a ClassB,
in ClassA you will have a code something like this

class ClassA {

    ClassB classB;

    public static void main(String args[]) {
        // instantiate a factory by connecting to some factory
        SomeFactory factory = //connect to some factory

        // use the factory to get an instance of "classB" and assign it to a variable;
        classB = factory.getBean("classB");

        // classB has now a reference, you can now call methods on classB.
        classB.callMethods();

    }
}

while a Dependency Injection is when your class is given a dependency by some factory or framework
example ClassA has a ClassB,

class ClassA {

    // "classB" is given a reference by some configuration outside our code (XML file), or can be configured using annotations.
    ClassB classB;

    public static void main() {        
        // classB has now a reference, you can now call methods on classB.
        classB.callMethods();
    }
}

you can see in Dependency Injection that the framework was responsible for injecting the instance of ClassB.

[Leonardo Carreira]

sorry i have any question about "DI/IoC"..

if iam using Spring..
is it DI make our application to use Singleton Object?..

and how to i make a Singleton Object in spring?..

example i have class : com.leonardo.action.SomeAction

how to configure ir in a spring context to be an singleton object?..
and how to use it in my application?..

CMIIW.
Thank's

Regards,
W
(Sorry my english isn't too good )

[kurt hanni]

Hi Leonardo, by default all objects created by spring are singleton, so you don't have do anything in your configuration.

If you want to see the configuration, you can specify it in the "scope" attribute of <bean> tag.

<bean id="hello" class="Hello" scope="singleton" />

you also specify in scope attribute if you want nonsingleton beans.

[Leonardo Carreira]

kurt hanni wrote:Hi Leonardo, by default all objects created by spring are singleton, so you don't have do anything in your configuration.

If you want to see the configuration, you can specify it in the "scope" attribute of <bean> tag.

<bean id="hello" class="Hello" scope="singleton" />

you also specify in scope attribute if you want nonsingleton beans.

Alright, thank's for your reply ..
now, how to get (use) bean which named "hello" in our application?..

is it just like this?

public class MyClass {
private Hello helo;

public void setHello(Hello hello){
this.hello=hello;
}

public doWork{
hello.print("-X-"); //example method
//any code
}
}

Thank's before
(sorry my english isn't too good)

[Mark Spritzler]

Yes and no, I like the code of MyClass, the next part is how you tell Spring there is the dependency between MyClass and the Hello class.

You can define another bean of type MyClass in your configuration and use a <property> tag in that <bean> tag that points or "ref"s references your "hello" bean. That is if you want it defined in the xml.

The other choice is to use Annotations. the @Autowired (Spring annotation) or the @Resource (JSR-250 annotation) does the trick. But to use annotations you have to put in the xml file that you are using annotations.

Now, if MyClass is not going to be a Spring Bean, then in MyClass you need to get a reference to the ApplicationContext object and call the getBean(String beanName) method.

Mark