自动装配

Spring IOC 容器可以自动装配Bean.在 <bean> 的 autowire 属性里指定自动装配的模式

byType(根据类型自动装配): 若 IOC 容器中有多个与目标 Bean 类型一致的 Bean. 在这种情况下, Spring 将无法判定哪个 Bean 最合适该属性, 所以不能执行自动装配.

byName(根据名称自动装配): 必须将目标 Bean 的名称和属性名设置的完全相同.

缺点

在 Bean 配置文件里设置autowire 属性进行自动装配将会装配 Bean 的所有属性. 然而, 若只希望装配个别属性时,autowire 属性就不够灵活了.

autowire 属性要么根据类型自动装配, 要么根据名称自动装配, 不能两者兼而有之.

一般情况下，在实际的项目中很少使用自动装配功能，因为和自动装配功能所带来的好处比起来，明确清晰的配置文档更有说服力一些

Main

package com.spring.beans.autowire;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {

	public static void main(String[] args) {
		ApplicationContext ac = new ClassPathXmlApplicationContext("/com/spring/beans/autowire/beans-autowire.xml");
		Person p = (Person)ac.getBean("person");
		System.out.println(p);
	}
}
/*
Car's constructor
Person [name=Tom, address=null, car=Car [brand=Audi, price=222333.0]]
*/

/com/spring/beans/autowire/beans-autowire.xml

<?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.xsd">
	
	<bean id="address1" class="com.spring.beans.autowire.Address"
    p:city="Beijing" p:street="Hilongguan"></bean>
    
    <bean id="car" class="com.spring.beans.autowire.Car" 
    p:brand="Audi" p:price="222333"></bean>
    <!-- 
    	可以使用autowire属性指定自动装配的方式，
    	byName根据bean的名字和当前bean的setter风格的属性名进行自动装配 ，若有匹配则进行自动装配，没有匹配，则不装配
    	byType根据bean的类型和当前bean的属性的类型进行自动装配，若IOC容器中有一个以上的类型匹配的bean，则抛异常
    -->
    <bean id="person" class="com.spring.beans.autowire.Person"
    p:name="Tom" autowire="byName"></bean>

</beans>

Person

package com.spring.beans.autowire;

public class Person {
	
	private String name;
	private Address address;
	private Car car;
	
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Address getAddress() {
		return address;
	}
	public void setAddress(Address address) {
		this.address = address;
	}
	public Car getCar() {
		return car;
	}
	public void setCar(Car car) {
		this.car = car;
	}
	@Override
	public String toString() {
		return "Person [name=" + name + ", address=" + address + ", car=" + car + "]";
	}
}

Address

package com.spring.beans.autowire;

public class Address {
	private String city;
	private String street;
	public String getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}
	public String getStreet() {
		return street;
	}
	public void setStreet(String street) {
		this.street = street;
	}
	@Override
	public String toString() {
		return "Address [city=" + city + ", street=" + street + "]";
	}
	
}

Car

package com.spring.beans.autowire;

public class Car {
	private String brand;
	private double price;
	public String getBrand() {
		return brand;
	}
	public void setBrand(String brand) {
		this.brand = brand;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	@Override
	public String toString() {
		return "Car [brand=" + brand + ", price=" + price + "]";
	}
	public Car() {
		System.out.println("Car's constructor");
	}
	
}