Using Spring Expression Language (SpEL) we can inject object references or values into a bean dynamically when the bean is created instead of statically defined at development time. In this example you’ll learn how to inject a bean’s property using a property of another bean.

Let start by create two classes, the Student and Grade classes. The student object will have a property to store their grade name which will be obtained from the grade object.

package org.kodejava.spring.core.el;

public class Student {
    private String name;
    private String grade;

    public Student() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGrade() {
        return grade;
    }

    public void setGrade(String grade) {
        this.grade = grade;
    }
}

package org.kodejava.spring.core.el;

public class Grade {
    private String name;
    private String description;

    public Grade() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}

Next we create the spring configuration file. In this configuration we have two beans definition, the grade and student bean. We set the name and description property of the grade bean.

We also set the name property of student bean using a string literal. But the grade property value is set to the grade‘s bean name property using the Spring EL, #{grade.name}. The expression tells the spring container to look for a bean whose id is grade, read its name and assign it to student‘s grade.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="grade" class="org.kodejava.spring.core.el.Grade">
        <property name="name" value="Beginner" />
        <property name="description" value="A beginner grade." />
    </bean>
    <bean id="student" class="org.kodejava.spring.core.el.Student">
        <property name="name" value="Alice" />
        <property name="grade" value="#{grade.name}" />
    </bean>

</beans>

And then create the following program to execute the spring container and retrieve the student bean from it.

package org.kodejava.spring.core.el;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpELDemo {
    public static void main(String[] args) {
        try (ClassPathXmlApplicationContext context =
                     new ClassPathXmlApplicationContext("spel-example.xml")) {

            Student student = (Student) context.getBean("student");
            System.out.println("Name  = " + student.getName());
            System.out.println("Grade = " + student.getGrade());
        }
    }
}

This program will print the following output:

Name  = Alice
Grade = Beginner

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.3.23</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>5.3.23</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-support</artifactId>
        <version>5.3.23</version>
    </dependency>
</dependencies>