Constructor Injection (with Dependent Objects) Example Constructor Injection with Dependent Objects

Constructor injection and example

We can inject collection values through the constructor in the Spring framework. constructor-arg The element within can use three elements.

can be: List Set Map

Each collection can have values based on strings and based on non-string values. In this example, we take "forum" as an example, where A question can have multiple answers. There are a total of three pages:

Question.java applicationContext.xml Test.java

In this example, the list we use can contain duplicate elements, and you can use a set that contains only unique elements. However, you need to change the list set in applicationContext.xml and the list set in Question.java.

Question.java

This class contains three properties, two constructors, and the displayInfo() method to display information. Here, we use a list to contain multiple answers.

Example

package com.w3codebox;
import java.util.Iterator;
import java.util.List;
public class Question {}}
private int id;
private String name;
private List<String> answers;
public Question() {}
public Question(int id, String name, List<String> answers) {
　　　　super();
　　　　this.id = id;
　　　　this.name = name;
　　　　this.answers = answers;
}
public void displayInfo(){
　　　　System.out.println(id+" "+name);
　　　　System.out.println("answers are:");
　　　　Iterator<String> itr=answers.iterator();
　　　　while(itr.hasNext()){
　　　　　　　　System.out.println(itr.next());
　　　　}
}
}

applicationContext.xml

Here we use builder-The list element defines the list of args.

Example

<?xml version="1.0" encoding="UTF-8"?>
<beans
　　　　xmlns="http://www.springframework.org/schema/beans"
　　　　xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
　　　　xmlns:p="http://www.springframework.org/schema/p"
　　　　xsi:schemaLocation="http://www.springframework.org/schema/beans
　http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="q" class="com.w3codebox.Question">
<constructor-arg value="111">/constructor-arg>
<constructor-arg value="What is java?">/constructor-arg>
<constructor-arg>
<list>
<value>Java is a programming language</value>/value>
<value>Java is a Platform</value>/value>
<value>Java is an Island of Indonasia</value>/value>
</list>
</constructor-arg>
</bean>
</beans>

Test.java

This class retrieves a Bean from the applicationContext.xml file and calls the displayInfo method.

Example

package com.w3codebox;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
public class Test {
public static void main(String[] args) {
　　　　Resource r = new ClassPathResource("applicationContext.xml");
　　　　BeanFactory factory = new XmlBeanFactory(r);
　　　　
　　　　Question q = (Question) factory.getBean("q");
　　　　q.displayInfo();
　　　　
}
}

Constructor Injection (with Dependent Objects) Example Constructor Injection with Dependent Objects

Spring Tutorial

Constructor injection and example