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Wednesday, 3 October 2018

Bean reference example using spring expression language(Annotation) | Spring Tutorial

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Overview: Bean References in SpEL (Annotation)

The Spring Expression Language (SpEL) provides a seamless way to reference other managed Spring beans and access their properties directly at runtime. When working with annotation-driven configurations, you can use the @Value annotation to inject an entire bean reference or drill down into its specific fields and getter methods.

In this guide, you will learn how to reference Spring beans and extract nested properties using annotation configuration and SpEL.

Understanding Bean Reference Syntax

SpEL enables direct interaction with other beans registered in the Spring ApplicationContext:

Referencing Another Bean: You can reference a bean directly by its name inside the expression delimiter: @Value("#{addressBean}").
Accessing Nested Properties: Drill into bean properties directly using dot notation: @Value("#{addressBean.city}").
Invoking Bean Methods: Execute methods on the referenced bean dynamically: @Value("#{addressBean.getFullAddress()}").
Dynamic Bean Interconnection: Connect components cleanly without having to inject the entire bean object when you only need a single property value.

Step-by-Step Configuration

Define the Source Bean: Annotate your source class with @Component("beanName") and define its fields and getters.
Inject via @Value: In your dependent component, annotate your field using SpEL syntax referencing the source bean:
@Value("#{itemBean.price}")
Container Initialization: When the ApplicationContext starts, Spring evaluates the reference and assigns the resolved property value directly to the field.

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Bean reference example using spring expression language(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.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.state}")

    private String employeeState;

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

    private String fullAddress;

    @Value("#{address}")

    private Address address;

    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 Address getAddress()

    {

        return address;

    }

    public void setAddress(Address address)

    {

        this.address = address;

    }

    @Override

    public String toString()

    {

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

                + employeeState + ", fullAddress=" + fullAddress + ", address="

                + address + "]";

    }

}

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 02, 2018 9:27:41 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@736e9adb: startup date [Sun Sep 02 09:27:41 IST 2018]; root of context hierarchy

Sep 02, 2018 9:27:41 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, employeeState=TamilNadu, fullAddress=A220 Bridge Appartment,Chennai,TamilNadu, address=Address [street=A220 Bridge Appartment, city=Chennai, state=TamilNadu]]