JAVA EE: Spring Expression Language – Referencing Static Methods and Members [Annotation]

Friday, 26 October 2018

Spring Expression Language – Referencing Static Methods and Members [Annotation] | Spring Tutorial

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What is Spring Expression Language (SpEL)?

The Spring Expression Language (SpEL) is a powerful expression language that supports querying and manipulating an object graph at runtime. It allows you to evaluate expressions dynamically and inject dynamic values directly into your Spring beans.

In this guide, you will learn how to access and invoke static methods and static fields (such as constants or helper functions from classes like java.lang.Math) using SpEL with annotation configuration.

The Type Operator: T(...)

To access static fields or methods in SpEL, you use the special T() type operator. This operator specifies an instance of java.lang.Class.

Referencing Classes: For standard classes in the java.lang package, you can simply reference them by class name (e.g., T(Math)). For classes in other packages, provide the fully qualified package name.
Accessing Static Constants: Inject static fields or constants using the syntax: #{T(java.lang.Math).PI}.
Invoking Static Methods: Execute static utility methods directly in annotations using: #{T(java.lang.Math).random()}.

Injecting Values with @Value

By placing the @Value("#{...}") annotation over fields or setter methods in your Spring-managed components, Spring evaluates the expression during bean initialization and injects the computed result automatically:

Field Injection: Assign evaluated mathematical constants or random values directly to properties.
Cleaner Code: Eliminate boilerplate initialization logic by letting the Spring container resolve static values declaratively.

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Spring Expression Language – Referencing Static Methods and Members [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>

Address.java

package com.ram.model;

import org.springframework.stereotype.Component;

@Component("address")

public class Address

{

    public static String STATE = "Karnataka";

    public static String COUNTRY = "India";

    public static String getFullAddress()

    {

        return STATE + "," + COUNTRY;

    }

}

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;

    @Value("#{T(com.ram.model.Address).STATE}")

    private String employeeState;

    @Value("#{T(com.ram.model.Address).getFullAddress()}")

    private String employeeFullAddress;

    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 getEmployeeState()

    {

        return employeeState;

    }

    public void setEmployeeState(String employeeState)

    {

        this.employeeState = employeeState;

    }

    public String getEmployeeFullAddress()

    {

        return employeeFullAddress;

    }

    public void setEmployeeFullAddress(String employeeFullAddress)

    {

        this.employeeFullAddress = employeeFullAddress;

    }

    @Override

    public String toString()

    {

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

                + employeeState + ", employeeFullAddress=" + employeeFullAddress

                + "]";

    }

}

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;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

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

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

        System.out.println(employee);

    }

}

Output

Sep 26, 2018 10:12:23 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@736e9adb: startup date [Wed Sep 26 22:12:23 IST 2018]; root of context hierarchy

Sep 26, 2018 10:12:23 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

Employee [id=10, name=Peter, employeeState=Karnataka, employeeFullAddress=Karnataka,India]