The expression language version 3.0 is now a separate specification in Java EE 7. It allows the page author to reference the bean properties, invoke methods, and perform arithmetic operations in the page description language. Originally, EL was a part of the JavaServer Pages specification, and it also became useful for the JSF technology. There are two types of EL: immediate evaluation and deferred evaluation. JSP relied on the immediate form, whereas JSF—because of its lifecycle management of request and response—required a deferred form. EL 3.0 represents the final unification of these strategies.
EL is useful for the page authors so that the digital developer can reference the properties in the managed beans, CDI components, and reference methods in a controller. EL is also used to invoke methods in a controller. EL is used to retrieve values from the beans but it can also set values.