Spring依赖对象的构造函数注入实例

1. 依赖对象的构造方法注入

如果各类之间存在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, 我们的方案是员工HAS-A地址。 Address类对象将称为从属对象。让我们首先看一下Address类：

Address.java

此类包含三个属性, 一个构造函数和toString()方法以返回这些对象的值。

package com.srcmini;

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, name和address(从属对象), 两个构造函数和show()方法, 以显示当前对象(包括依赖对象)的记录。

package com.srcmini;

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, 以这种方式我们将依赖对象作为构造函数参数传递。

<?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.srcmini.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.srcmini.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.srcmini;

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();
		
	}
}

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