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Spring Framework Interview Questions

Unified Expression Language(EL) :

Unified EL has been added to JSTL to overcome problems when integrating JSP EL with the JSF EL.EL was used to access data objects in a simple way. It is used mainly as a short-hand for accessing values. Later it was included in JSP 2.0 with more functionality. When JSF was released it also needed EL.JSF and JSP each has its own Lethe JSP EL is much flexible to the web application developer but JSF people were unsatisfied by the JSP EL.One of the reason was that it requires JSP engine to evaluate expression at the appropriate time during the lifecycle, but JSP expressions are evaluated immediately. The second reason behind it was that JSP functions could only call static methods in TLD and they cannot be used to invoke public methods dynamically on server side objects during lifecycle to validate data and handle component events

So these were the reasons for developing such an EL that would work for both JSP and JSF and make using JSP and JSF together easier. This new EL is called unified EL. So this was inspired by EL used in JSTL and JSP. There is a package "el" in javax package that represents EL

In addition to the features already available in the JSP EL, unified EL has the following features :

  • Deferred evaluation of expressions i.e. evaluation of the expression at the appropriate time during the page lifecycle from JSP engine.

  • Support for expressions that can set and get values.

  • Support for expressions that can invoke methods.

  • A pluggable API for resolving expressions.



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