Spring SpEL - Functions

SpEL expression allows to create and use functions specific to expression using #function-name syntax. A function is set using registerFunction on EvaluationContext.

Syntax

context.registerFunction("reverse", 
   MainApp.class.getDeclaredMethod("reverse", new Class[] { String.class }));

Following example shows the various use cases.

Example - Usage of Projection in Collection in SpEL

Let's update the project created in Spring SpEL - Create Project chapter. We're updating following file −

• MainApp.java − Main application to run and test.

MainApp.java

Here is the content of MainApp.java file −

package com.tutorialspoint;

import java.text.ParseException;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

public class MainApp {
   public static void main(String[] args) throws ParseException, NoSuchMethodException, SecurityException {
      ExpressionParser parser = new SpelExpressionParser();
      StandardEvaluationContext context = new StandardEvaluationContext();

      context.registerFunction("reverse",
      MainApp.class.getDeclaredMethod("reverse", new Class[] { String.class }));

      String reverseString=parser.parseExpression("#reverse('main')").getValue(context, String.class);
      System.out.println(reverseString);
   }
   public static String reverse(String input) {
      StringBuilder backwards = new StringBuilder();
      for (int i = 0; i < input.length(); i++) {
         backwards.append(input.charAt(input.length() - 1 - i));
      }
      return backwards.toString();
   }
}

Output

Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message −

niam