Beans as Injectable Objects

The concept of injection has been part of Java technology for some time. Since the Java EE 5 platform was introduced, annotations have made it possible to inject resources and some other kinds of objects into container-managed objects. CDI makes it possible to inject more kinds of objects and to inject them into objects that are not container-managed.

The following kinds of objects can be injected:

• (Almost) any Java class

• Session beans

• Java EE resources: data sources, Java Message Service topics, queues, connection factories, and the like

• Persistence contexts (JPA EntityManager objects)

• Producer fields

• Objects returned by producer methods

• Web service references

• Remote enterprise bean references

For example, suppose that you create a simple Java class with a method that returns a string:

package greetings;

public class Greeting {
    public String greet(String name) {
        return "Hello, " + name + ".";
    }
}

This class becomes a bean that you can then inject into another class. This bean is not exposed to the EL in this form. Giving Beans EL Names explains how you can make a bean accessible to the EL.