如果类之间存在HAS-A关系，则首先创建依赖对象(包含对象)的实例，然后将其作为主类构造函数的参数传递。在这里，我们的场景是员工HAS-A地址。 Address类对象将称为从属对象。首先让我们看一下Address类:
Address.java
该类包含三个属性，一个构造函数和toString()方法以返回这些对象的值。
package com.nhooo;
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
它包含三个属性id，名称和地址(从属对象)，两个构造函数和show()方法来显示当前对象(包括依赖对象)的记录。
package com.nhooo;
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 属性用于定义另一个对象的引用，例如，我们将依赖对象传递为构造函数参数。
<?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.nhooo.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.nhooo.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
此类从applicationContext.xml文件获取Bean并调用show方法。
package com.nhooo;
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();
}
}