Dependency Injecting with constructors

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Dependency Injecting with constructors

Every instance in Java needs to call the constructor once in the lifetime. In Spring constructors can also be used to inject the various properties using the metadata. There are various ways we can supply the properties to the constructor of the bean.

Writing in sequence all the properties using <constructor-arg value/value-ref="XXX" /> tag.

Using the indexes in the <constructor-arg [index="0"] value/value-ref="XXX" /> tag.

Using the datatype to map the arguments with the parameters example <constructor-arg [type="datatype"] value/value-ref="XXX" />

The coming example will use the all three types in the same wiring.

Example :-

package com.visualbuilder.beans;

public class ConstructorInjectionBean {

private String name;

private int age;

private char sex;

    public ConstructorInjectionBean(){


}

    public ConstructorInjectionBean(String name, int age,char sex){


this.name=name;


this.age=age;


this.sex=sex;


}

    public void printData(){

        System.out.println( "Assigned Name is "+ name);

        System.out.println( "Assigned Age is "+ age);

        System.out.println( "Assigned Sex is "+ sex);


}

}

ConstructorInjectionExample.java

package com.visualbuilder.example;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.visualbuilder.beans.ConstructorInjectionBean;

public class ConstructorInjectionExample {

    public static void main (String [] ar){


ApplicationContext context = new ClassPathXmlApplicationContext(new String[] {"com/visualbuilder/xml/spring-beans.xml"});


ConstructorInjectionBean bean = (ConstructorInjectionBean)context.getBean("constructorInjection");

        bean.printData();


}

}

Output:-

Jun 1, 2008 7:07:47 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@c4bcdc: display name [org.springframework.context.support.ClassPathXmlApplicationContext@c4bcdc]; startup date [Sun Jun 01 19:07:47 IST 2008]; root of context hierarchy

Jun 1, 2008 7:07:47 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [com/visualbuilder/xml/spring-beans.xml]

Jun 1, 2008 7:07:47 PM org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory

INFO: Bean factory for application context [org.springframework.context.support.ClassPathXmlApplicationContext@c4bcdc]: org.springframework.beans.factory.support.DefaultListableBeanFactory@15e83f9

Bean is created

Assigned Name is John Smith

Assigned Age is 25

Assigned Sex is M

Jun 1, 2008 7:07:47 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons

INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@15e83f9: defining beans [test,collectionExample,typeCollectionExample,constructorInjection,setterInjection]; root of factory hierarchy