Introduction to Jakarta Expression Language API

Jakarta Expression Language (EL) is an API for accessing and operating JavaBeans or other objects in an expression.In the development of Java Web, EL is a very practical tool. For example, in the JSP page, the data that can be transmitted at the back end can be accessed and operated through EL. Jakarta Expression Language provides a simple way to obtain and set the attribute values of the object, execute methods, perform mathematical calculations, operate collection and array, etc.EL is embedded in JSP and JSF, which can easily access and operate the attributes of the objects through page expressions. The following is a simple EL expression example: ${person.name} In the above example, EL expression `$ {person.name}` is used to obtain the value of the "name" property called "Person" object.This expression can be directly embedded in the JSP page. When the page is rendered, the EL engine will automatically analyze and execute this expression, and eventually insert the attribute value into the generated HTML. In addition to the access of object attributes, EL also supports other operations, such as method calls and arithmetic operations.Here are some examples of EL: $ {Person.getName ()} // Call the getName () method to get the attribute value $ {2 + 2} // Execute mathematics operations $ {list.size ()} // Call the set of the set to get the size $ {Array [0]} // Access elements of the array Jakarta Expression Language API also provides some built -in functions and operators, which can be used for string operations, date processing and collection operations.For example: $ {fn: length (string)} // Get the length of the string $ {Empty (List)} // Check whether the set is empty $ {Not Booleanvalue} // Reverse the BOOLEAN value To sum up, Jakarta Expression Language API is a very useful tool that can easily access and operate the attribute values, execute methods and various operations in the Java Web development.By using EL, developers can build dynamic web applications more efficiently and simplify the interaction of pages and back -end data.