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What is EL? – Description and usage of Expression Language
Introduction:
Expression Language (EL) is a scripting language introduced in JavaServer Pages (JSP) and JavaServer Faces (JSF) technologies. It is designed to simplify the access and manipulation of data stored in JavaBeans components or other managed objects within the web applications. EL provides a concise syntax and powerful set of operators that enable developers to evaluate expressions and access data dynamically at runtime.
Usage of Expression Language:
1. Accessing and Manipulating Managed Bean Properties:
One of the primary purposes of EL is to access and manipulate properties of JavaBeans or managed objects. EL expressions can directly reference these properties using the dot (.) operator. For example, if we have a managed bean named “user” with a property “name”, we can access it using the EL expression ${user.name}.
We can further perform operations like setting values on properties using the EL expressions. For example, to set a value to the “name” property, we can use ${user.name = ‘John’}.
2. Evaluating Simple and Complex Expressions:
EL supports the evaluation of both simple and complex expressions. Simple expressions can be evaluated within tags like ${expression} or #{expression}, where expressions can include literals, variables, or function calls.
Complex expressions, on the other hand, enable developers to perform more advanced operations like arithmetic calculations, comparisons, logical operations, and conditional statements. For example, an EL expression ${(num1 lt num2) ? ‘Less than’ : ‘Greater than or equal to’} can be used to compare the values of num1 and num2 and return the appropriate result.
3. Iterating and Accessing Collections:
Another useful feature of EL is its ability to iterate over collections and access their elements. EL provides special syntax to loop over collections, such as ${item} or ${userList}.
Additionally, EL provides built-in functions to access the length and iterate over arrays, lists, and maps. For instance, the EL expression ${fn:length(userList)} can be used to retrieve the length of a list named “userList”.
Conclusion:
Expression Language (EL) is a powerful scripting language that simplifies the access and manipulation of data within JavaServer Pages (JSP) and JavaServer Faces (JSF) web applications. It facilitates the evaluation of expressions, accessing properties of managed beans, performing arithmetic and logical operations, and iterating over collections. By leveraging EL, developers can write more concise and dynamic code, enhancing the overall functionality and flexibility of their web applications.
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