Explore the advanced functions and applications of Expression Language 3.0 API

Expression Language (EL) 3.0 is an expression language introduced in the Java Enterprise Edition (Java EE) specification for evaluating and operating data in Web applications.EL 3.0 API provides many advanced functions and applications, enabling developers to process data and expressions more flexibly. One of the most important features of the EL 3.0 API is to support LAMBDA expressions and method references in the expression.Lambda expression is a concept of functional programming, which can be passed as a parameter to the method or stored in the variable.Using Lambda expression, you can write more concise and flexible code in EL expressions to process data. The following is an example of EL expression using Lambda expression: // Create a variable called "Users", it is a list containing multiple User objects List<User> users = getUsers(); // Use Lambda expressions to screen for users older than 18 years old List<User> adults = (List<User>) expressionFactory.createValueExpression( ELContext.getCurrent(), "#{users.stream().filter(user -> user.getAge() > 18).collect(Collectors.toList())}", List.class).getValue(ELContext.getCurrent()); The EL expression in the above example uses Lambda expressions to screen the user list, and only returns users who are older than 18 years old.By using Lambda expressions, we can define the screening conditions in a more concise and readability. In addition to Lambda expression, EL 3.0 also introduces the concept of method reference.Methods Quote allowing developers to directly quote the existing methods in EL expressions without writing LAMBDA expressions.This is very useful for calling a specific method in an expression. The following is an example of EL expression cited by usage: // Define a variable called "Message", it is a string String message = "Hello World"; // Use how to reference the length of the string int length = (int) expressionFactory.createValueExpression( ELContext.getCurrent(), "#{message.length()}", int.class).getValue(ELContext.getCurrent()); The EL expression in the above example uses method reference to obtain the length of the string "Hello World".If you use it, we can directly use the existing method to process the data without writing an additional Lambda expression. In addition, the EL 3.0 API also provides some new functions for processing collection and array.These functions can be directly called in EL expressions, thereby simplifying the operation of collection and array. The following is an example of a new function using EL 3.0: // Define a variable called "NUMBERS", which is a list containing multiple integers List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); // Use the sum of all elements in the list of new functions int sum = (int) expressionFactory.createValueExpression( ELContext.getCurrent(), "#{numbers.sum()}", int.class).getValue(ELContext.getCurrent()); The EL expression in the above example uses the new function "SUM ()" to calculate the sum of all elements in the list.The new functions of EL 3.0 can greatly simplify the operation of collection and array. Expression Language 3.0 API's advanced features and applications enable developers to evaluate and operate data in a more flexible and concise way.By supporting LAMBDA expression and method reference, and providing new functions for processing collection and array, EL 3.0 greatly improves the programming efficiency and code readability of developers.When developing web applications, you can make full use of EL 3.0 to process data and expressions.