What is Constructor Auto-wiring mode in Spring?

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What is Constructor Auto-wiring mode in Spring?

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>5.0.2.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;

public class Address
{
    private String city;
    private String state;
    private String country;

    public Address(String city, String state, String country)
    {
        this.city = city;
        this.state = state;
        this.country = country;
    }

    @Override
    public String toString()
    {
        return "Address [city=" + city + ", state=" + state + ", country="
                + country + "]";
    }

}

Employee.java

package com.ram.model;

public class Employee
{
    private String name;
    private Address address;

    public Employee(String name)
    {
        System.out.println("Employee(String name) constructor "
                + "is called by the Spring container");
        this.name = name;
    }

    public Employee(String name, Address address)
    {
        System.out.println("Employee(String name, Address address) "
                + "constructor is called by the Spring container");
        this.name = name;
        this.address = address;
    }

    public void displayEmployeeDetails()
    {
        System.out.println(
                "Employee [name=" + name + ", address=" + address + "]");
    }

}

applicationContext.xml

<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-4.3.xsd">

    <bean id="address" class="com.ram.model.Address" >
        <constructor-arg value="Chennai"></constructor-arg>
        <constructor-arg value="Tamil Nadu"></constructor-arg>
        <constructor-arg value="India"></constructor-arg>
    </bean>

    <bean id="employee" class="com.ram.model.Employee" autowire="constructor">
        <constructor-arg value="Peter"></constructor-arg>
    </bean>

</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]");
       
        employee.displayEmployeeDetails();
    }

}

Output

Jul 01, 2018 10:27:21 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sun Jul 01 10:27:21 IST 2018]; root of context hierarchy
Jul 01, 2018 10:27:21 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
Employee(String name, Address address) constructor is called by the Spring container
---------------------------------------
Got employee object from the ApplicationContext[Spring Container]
Employee [name=Peter, address=Address [city=Chennai, state=Tamil Nadu, country=India]

Click the below link to download the code:
https://sites.google.com/site/ramj2eev2/java_basics/SpringDemo_Constructor_Autowiring.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/javaee/tree/master/Spring_2018/SpringDemo_Constructor_Autowiring

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/a2a3948db9c8932cede027a3aaf7ba5a87170ed8/Spring_2018/SpringDemo_Constructor_Autowiring/?at=master

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