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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
例子:
新建一个包名为:com.yorkmass.spring.beans.autowire
新建Address类
package com.yorkmass.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 + "]";
}
}
新建Car类
package com.yorkmass.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 + "]";
}
}
新建Person类
package com.yorkmass.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 + "]";
}
}
新建spring xml配置文件,文件名: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="address" class="com.yorkmass.spring.beans.autowire.Address"
p:city="beijing" p:street="wudaokou"></bean>
<!--
用byType自动装配当出现两个以上同类型匹配项时,会抛异常
<bean id="address2" class="com.yorkmass.spring.beans.autowire.Address"
p:city="tangshan" p:street="caofeidian"></bean>
-->
<bean id="car" class="com.yorkmass.spring.beans.autowire.Car"
p:brand="audi" p:price="30000"></bean>
<!--
<bean id="person" class="com.yorkmass.spring.beans.autowire.Person"
p:name="tom" p:address-ref="address" p:car-ref="car"></bean>
-->
<!--
可以使用autowire属性指定自动装配的方式
byName根据当前bean的setter风格的属性名进行自动装配,若有匹配的,则进行自动装配,没有不装配
代码:<bean id="person" class="com.yorkmass.spring.beans.autowire.Person"
p:name="tom" autowire="byName"></bean>
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容器中有一个以上类型匹配则抛异常
代码:<bean id="person" class="com.yorkmass.spring.beans.autowire.Person"
p:name="tom" autowire="byType"></bean>
-->
<bean id="person" class="com.yorkmass.spring.beans.autowire.Person"
p:name="tom" autowire="byType"></bean>
</beans>
新建主类Main
package com.yorkmass.spring.beans.autowire;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
ApplicationContext ctx=new ClassPathXmlApplicationContext("beans-autowire.xml");
Person person=(Person)ctx.getBean("person");
System.out.println(person);
}
}