自动装配

XML 配置里的 Bean 自动装配

Spring IOC 容器可以自动装配 Bean. 需要做的仅仅是在 <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.

constructor(通过构造器自动装配): 当 Bean 中存在多个构造器时, 此种自动装配方式将会很复杂. 不推荐使用

 

XML 配置里的 Bean 自动装配的缺点

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

<?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.learn.spring.autowire.Address">
		<property name="city" value="BeiJing" ></property>
		<property name="street" value="HuiLongGuan"></property>
	</bean>
	
	<bean id="address2" class="com.learn.spring.autowire.Address">
		<property name="city" value="ShangHai" ></property>
		<property name="street" value="PuDong"></property>
	</bean>
	
	
	<bean id="car" class="com.learn.spring.autowire.Car" p:brand="Audi" p:price="400000">
	</bean>
	
	<!-- 
		autowire:
			byName: 通过bean的id值与要进行注入的属性名进行匹配
			byType: 通过bean的class值与要进行注入的属性的类型进行匹配.
	 -->
	<bean id="person" class="com.learn.spring.autowire.Person" autowire="byType">
		<property name="name" value="Tom"></property>
	</bean>
	
	

</beans>

package com.learn.spring.autowire;

public class Address {
	private String city ;
	private String street ;
	
	public Address() {
		// TODO Auto-generated constructor stub
		System.out.println("Address 's  Constructor ......");
	}
	
	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 + "]";
	}
	
	
}

package com.learn.spring.autowire;

public class Car {
	private String brand ;
	private double price ;
	public Car() {
		// TODO Auto-generated constructor stub
	}
	
	public Car(String brand, double price) {
		super();
		this.brand = brand;
		this.price = 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 + "]";
	}
	
	
}

package com.learn.spring.autowire;

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

public class Main {
	public static void main(String[] args) {
		//1.实例化容器
		ApplicationContext ctx = 
				new ClassPathXmlApplicationContext("spring-autowire.xml");
		//2.从容器中获取bean
		Person person = (Person)ctx.getBean("person");
		System.out.println(person);
	}
}

package com.learn.spring.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
				+ "]";
	} 
	
	
}