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If there is a HAS-A relationship between classes, create an instance of the dependent object (containing object) first, and then pass it as a parameter to the constructor of the main class. In this scenario, our scenario is employee HAS-A address. The Address class object will be called a dependent object. Let's first take a look at the Address class:
Address.java
This class contains three properties, a constructor, and a toString() method to return the values of these objects.
package com.w3codebox;
public class Address {
private String city;
private String state;
private String country;
public Address(String city, String state, String country) {
super();
this.city = city;
this.state = state;
this.country = country;
}
public String toString(){
return city + " " + state + " " + country;
}
}
Employee.java
It contains three properties: id, name, and address (dependent object), two constructors, and a show() method to display the record of the current object (including dependent objects).
package com.w3codebox;
public class Employee {
private int id;
private String name;
private Address address; // Aggregation
public Employee() {System.out.println("def cons");}
public Employee(int id, String name, Address address) {
super();
this.id = id;
this.name = name;
this.address = address;
}
void show(){
System.out.println(id+" "+name);
System.out.println(address.toString());
}
}
applicationContext.xml
ref L'attributo viene utilizzato per definire un riferimento ad un altro oggetto, ad esempio, passeremo l'oggetto di dipendenza come parametro del costruttore.
<?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="a1" class="com.w3codebox.Address"> <constructor-arg value="ghaziabad"></constructor-arg> <constructor-arg value="UP"></constructor-arg> <constructor-arg value="India"></constructor-arg> </bean> <bean id="e" class="com.w3codebox.Employee"> <constructor-arg value="12" type="int"></constructor-arg> <constructor-arg value="Sonoo"></constructor-arg> <constructor-arg> <ref bean="a1"/> </constructor-arg> </bean> </beans>
Test.java
Questa classe recupera un Bean dal file applicationContext.xml e chiama il metodo show.
package com.w3codebox;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.*;
public class Test {
public static void main(String[] args) {
Resource r = new ClassPathResource("applicationContext.xml");
BeanFactory factory = new XmlBeanFactory(r);
Employee s = (Employee) factory.getBean("e");
s.show();
}
}