Jakarta expression language API in the Java class library: detailed introduction and example

Jakarta Expression Language (EL) API is a standard API for handling expressions in Java.It provides a simple and flexible way to evaluate and operate the attributes or methods of the Java object.This article will introduce the usage of the Jakarta El API in detail and give some examples to help readers understand. Jakarta El API is a way to interact with Java objects through expression language.It is widely used in the container environment of the Java EE platform, especially associated with the JavaseerVer Pages (JSP) technology.Through the Jakarta El API, we can obtain variable values, execution methods, operation sets, etc. from the page. Using Jakarta El API, we can achieve complex logic in several lines of code.It provides a variety of expression operators and functions, which can easily process data types such as strings, numbers, and dates.The basic usage of Jakarta El API is one of the essential skills developed by Java Web. Here are some examples of usage to explain the usage of Jakarta El API: 1. Visit the attributes of the Java object: In EL expressions, we can use the "." Operator to access the attributes of the Java object.For example, suppose we have an object called Person, which has an name property.Through the Jakarta El API, we can use the following code to obtain the value of the name property: String name = (String) el.evaluate("${person.name}"); 2. The method of calling the Java object: In addition to access attributes, we can also use EL expressions to call Java objects.For example, suppose we have an object called User, and it has a getName () method.Through the Jakarta El API, we can use the following code to call this method and get the return value: String name = (String) el.evaluate("${user.getName()}"); 3. Access set element: Using the Jakarta El API, we can easily obtain the elements of specific indexes in the set.For example, assuming we have a list called Numbers, we can use the following code to obtain the element of indexing 0 in the list: int firstNumber = (int) el.evaluate("${numbers[0]}"); 4. Computing symbols and functions: The Jakarta El API also provides a series of operations and functions that can be used to perform various operations.For example, we can use arithmetic operator for mathematics calculation, and compare the relationship operators.In addition, it also provides a set of internal functions such as conversion functions, date functions, etc. If we need to use the Jakarta El API, we need to add the relevant library files to the project path.In the Java EE environment, this is usually implemented by adding corresponding dependencies. To sum up, Jakarta Exposition Language (EL) API is a convenient and powerful tool for handling expressions in Java.It provides simple grammar and rich functions, which can greatly simplify the writing and maintenance of code.By understanding and proficient in the use of the Jakarta El API, developers can develop Java Web more efficiently.