Basis of Dependency injection framework

Question

I want to write my own simple DI framework. I want that it perform only this simple case like Spring does:

public interface IWriter {
    public void writer(String s);
}

@Service
public class MySpringBeanWithDependency {
    private IWriter writer;

    @Autowired
    public void setWriter(IWriter writer) {
        this.writer = writer;
    }

    public void run() {
        String s = "This is my test";
        writer.writer(s);
    }
}

@Service
public class NiceWriter implements IWriter {
    public void writer(String s) {
        System.out.println("The string is " + s);
    }
}

public class Main extends TestCase {

    @Test
    public void test() {

        ApplicationContext context = new ClassPathXmlApplicationContext(
                "META-INF/beans.xml");
        MySpringBeanWithDependency test = (MySpringBeanWithDependency) context
                .getBean("mySpringBeanWithDependency");
        test.run();
    }
}

The same case, but mb without an XML-file.

Can somebody explain the concept of this type of frameworks and write some code.

A lot of interfaces and their huge implementations make it very hard. At all, it is too complex for newbie. — itun, Nov 29 '11 at 23:02

score 3 · Accepted Answer · answered Nov 29 '11 at 23:01

Guice is open source. You can browse the code here: http://code.google.com/p/google-guice/source/browse/

Spring is also open source. You can download it here: http://www.springsource.org/download

Browsing through either of these should satisfy the "write some code" part of your question.

EDIT: It seems you are looking for the "magic". It boils down to reflection. Spring and/or Guice use Java Reflection to find the appropriate setters (or fields) on the class and set the values. That's it. Everything else is glue to make the whole system work.

Basis of Dependency injection framework

1 Answers1