JAVA EE: Spring expression language method invocation (Annotation) | Spring Tutorial

Thursday, 4 October 2018

Spring expression language method invocation (Annotation) | Spring Tutorial | Spring Framework

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Overview: Method Invocation in SpEL

The Spring Expression Language (SpEL) allows you to invoke methods on beans or literal objects dynamically at runtime. When using annotation-driven configuration, you can execute methods—both with or without arguments—and inject their return values directly into target bean properties using the @Value annotation.

In this guide, you will learn how to invoke methods on Spring beans and Java types using annotation-based SpEL configuration.

Understanding Method Invocation Syntax

SpEL supports standard Java method call syntax inside expression delimiters:

Invoking Bean Methods: Call methods directly on managed beans: @Value("#{beanName.methodName()}").
Passing Arguments: Pass literal values, expressions, or other bean references as arguments: @Value("#{beanName.calculateDiscount(100)}").
Calling Methods on Literals: Execute standard Java methods directly on literal types: @Value("#{'Ram N Java'.toUpperCase()}").
Method Chaining: Chain multiple calls seamlessly within the expression: @Value("#{beanName.getName().trim().toLowerCase()}").

Step-by-Step Configuration

Define the Target Bean & Method: Create a component with the business method whose output you need to capture.
Apply @Value Annotation: In the consuming bean, annotate your property with the method call expression inside @Value("#{...}").
Run the Application Context: Spring executes the method during bean initialization and injects the resulting value into the annotated field.

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Spring expression language method invocation (Annotation) | Spring Tutorial | Spring Framework

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.beans.factory.annotation.Value;

import org.springframework.stereotype.Component;

@Component("address")

public class Address

{

    @Value("A220 Bridge Appartment")

    private String street;

    @Value("Chennai")

    private String city;

    @Value("TamilNadu")

    private String state;

    public String getStreet()

    {

        return street;

    }

    public void setStreet(String street)

    {

        this.street = street;

    }

    public String getCity()

    {

        return city;

    }

    public void setCity(String city)

    {

        this.city = city;

    }

    public String getState()

    {

        return state;

    }

    public void setState(String state)

    {

        this.state = state;

    }

    public String getFullAddress()

    {

        return street + "," + city + "," + state;

    }

    @Override

    public String toString()

    {

        return "Address [street=" + street + ", city=" + city + ", state="

                + state + "]";

    }

}

Employee.java

package com.ram.model;

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

import org.springframework.stereotype.Component;

@Component("employee")

public class Employee

{

    @Value("100")

    private int id;

    @Value("Peter")

    private String name;

    @Value("#{address.getFullAddress()}")

    private String fullAddress;

    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 getFullAddress()

    {

        return fullAddress;

    }

    public void setFullAddress(String fullAddress)

    {

        this.fullAddress = fullAddress;

    }

    @Override

    public String toString()

    {

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

                + fullAddress + "]";

    }

}

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(

                "Got employee object from the ApplicationContext(Spring Container)");

        System.out.println(employee);   

    }

}

Output

Sep 03, 2018 10:37:42 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@736e9adb: startup date [Mon Sep 03 10:37:42 IST 2018]; root of context hierarchy

Sep 03, 2018 10:37:42 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

Got employee object from the ApplicationContext(Spring Container)

Employee [id=100, name=Peter, fullAddress=A220 Bridge Appartment,Chennai,TamilNadu]