JAVA EE: The regular expression in Spring Expression Language SpEL [Annotation]

Friday, 26 October 2018

The regular expression in Spring Expression Language SpEL [Annotation] | Spring Tutorial

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Overview: Regex with Spring Expression Language (SpEL)

The Spring Expression Language (SpEL) provides powerful evaluation capabilities, including built-in pattern matching using regular expressions. This allows you to evaluate strings against complex patterns dynamically at application startup or bean initialization.

In this guide, you will learn how to evaluate regular expressions directly using SpEL and inject the resulting boolean verification flag into your Spring beans using the @Value annotation.

Understanding the 'matches' Operator

SpEL introduces the intuitive matches keyword to perform regular expression checks directly within expression definitions.

Pattern Syntax: The syntax follows the format 'inputString' matches 'regexPattern'.
Boolean Output: If the string matches the specified pattern, SpEL evaluates to true; otherwise, it resolves to false.
Validation Scenarios: Ideal for validating formatted strings like email addresses, phone numbers, or zip codes during bean setup.

Configuring Pattern Matching with @Value

You can annotate your component's fields or setter methods to evaluate regex patterns automatically:

Annotation Declaration: Annotate a boolean field with @Value("#{customer.email matches '[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,4}'}").
Dynamic Evaluation: Spring inspects the bean property, runs the regex match, and assigns the boolean outcome directly to your field.

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The regular expression in Spring Expression Language SpEL [Annotation] | Spring Tutorial

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.5.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

Email.java

package com.ram.model;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.stereotype.Component;

@Component("email")

public class Email

{

    @Value("ram@yahoo.com")

    private String emailId;

    @Value("100")

    private String contentId;

    public String getEmailId()

    {

        return emailId;

    }

    public void setEmailId(String emailId)

    {

        this.emailId = emailId;

    }

    public String getContentId()

    {

        return contentId;

    }

    public void setContentId(String contentId)

    {

        this.contentId = contentId;

    }

    @Override

    public String toString()

    {

        return "Email [emailId=" + emailId + ", contentId=" + contentId + "]";

    }

}

Employee.java

package com.ram.model;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.stereotype.Component;

@Component("employee")

public class Employee

{

    @Value("10")

    private int id;

    @Value("Peter")

    private String name;

    private String digitRegEx = "\\d+";

    private String emailRegEx = "^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)"

            + "*@[A-Za-z0-9]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";

    @Value("#{email.emailId matches employee.emailRegEx}")

    private String isValidEmail;

    @Value("#{email.contentId matches employee.digitRegEx}")

    private String isValidContentId;

    public int getId()

    {

        return id;

    }

    public void setId(int id)

    {

        this.id = id;

    }

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public String getDigitRegEx()

    {

        return digitRegEx;

    }

    public void setDigitRegEx(String digitRegEx)

    {

        this.digitRegEx = digitRegEx;

    }

    public String getEmailRegEx()

    {

        return emailRegEx;

    }

    public void setEmailRegEx(String emailRegEx)

    {

        this.emailRegEx = emailRegEx;

    }

    public String getIsValidEmail()

    {

        return isValidEmail;

    }

    public void setIsValidEmail(String isValidEmail)

    {

        this.isValidEmail = isValidEmail;

    }

    public String getIsValidContentId()

    {

        return isValidContentId;

    }

    public void setIsValidContentId(String isValidContentId)

    {

        this.isValidContentId = isValidContentId;

    }

    @Override

    public String toString()

    {

        return "Employee [id=" + id + ", name=" + name + ", isValidEmail="

                + isValidEmail + ", isValidContentId=" + isValidContentId + "]";

    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

    xmlns:context="http://www.springframework.org/schema/context"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

    <context:component-scan base-package="com.ram" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

import com.ram.model.Email;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Email email = (Email) context.getBean("email");

        System.out.println(email + "\n");

        Employee employee = (Employee) context.getBean("employee");

        System.out.println(employee);

    }

}

Output

Sep 21, 2018 9:44:02 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@736e9adb: startup date [Fri Sep 21 09:44:02 IST 2018]; root of context hierarchy

Sep 21, 2018 9:44:02 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

---------------------------------------

Email [emailId=ram@yahoo.com, contentId=100]

Employee [id=10, name=Peter, isValidEmail=true, isValidContentId=true]