Spring2.x中设置Bean的作用域

在配置文件里声明的Bean时，实际定义的并不是一个Bean实例，而是为Bean创建了一个模板，当通过getBean()调用或其他请求改Bean的时候，Spring将根据Bean的实际作用域返回Bean的实例，在某些情况下默认的作用域并不适合，此时需要为Bean设置一个更适合的作用域。
在Spring2.x里，可以通过<bean>中的scope属性设置作用域，默认情况下Spring只为在Ioc容器里声明的Bean创建一个实例，整个Ioc范围内都共享这个实例，所有后续的getBean()调用和引用该实例，都将返回这个唯一的Bean实例。这个作用域称为singleton,是默认的作用域。
Spring2.x中Bean的几种作用域：
1、singleton————–为每个Spring Ioc容器创建一个Bean实例；
2、prototype————-每次请求时都创建一个新的实例；
3、request—————每个HTTP请求创建一个Bean实例，这个作用域仅在WEB应用程序的上下文中有效；
4、session—————每个HTTP请求创建一个Bean实例，这个作用域仅在WEB应用程序的上下文中有效；
5、globalSession——为每个全局的HTTP会话创建一个Bean实例，这个作用域尽在门户应用程序的上下文中有效；
下边将用一个商品购物车例子来说明这个Bean的实例作用域：
[java] view plaincopyprint?
package com.song.spring.scope;

public abstract class Product {

private String name;
private double price;

public Product(){}

public Product(String name, double price){
this.name = name;
this.price = price;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public double getPrice() {
return price;
}

public void setPrice(double price) {
this.price = price;
}

public String toString(){
return name + ” ” + price;
}
}

[java] view plaincopyprint?
package com.song.spring.scope;

public class Battery extends Product {

private boolean rechargeable;

public Battery(){
super();
}

public Battery(String name, double price){
super(name, price);
}

public boolean isRechargeable() {
return rechargeable;
}

public void setRechargeable(boolean rechargeable) {
this.rechargeable = rechargeable;
}

}

[java] view plaincopyprint?
package com.song.spring.scope;

public class Disc extends Product {

private int capacity;

public Disc(){
super();
}

public Disc(String name, double price){
super(name, price);
}

public int getCapacity() {
return capacity;
}

public void setCapacity(int capacity) {
this.capacity = capacity;
}

}

接下来创建一个无购物车实例；
[java] view plaincopyprint?
package com.song.spring.scope;

import java.util.ArrayList;
import java.util.List;

public class ShoppingCart {

private List<Product> items = new ArrayList<Product>();

public void addItem(Product item){
items.add(item);
}

public List<Product> getItem(){
return items;
}
}

在classpath:下的xml文件applicationContext.xml中的Bean配置为：
[html] view plaincopyprint?
<?xml version=”1.0″ encoding=”UTF-8″?>
<!DOCTYPE beans PUBLIC “-//SPRING//DTD BEAN 2.0//EN”
“http://www.springframework.org/dtd/spring-beans-2.0.dtd”>
<beans>
<bean id=”aaa” class=”com.song.spring.scope.Battery”>
<property name=”name” value=”AAA” />
<property name=”price” value=”2.5″ />
</bean>

<bean id=”cdrw” class=”com.song.spring.scope.Disc”>
<property name=”name” value=”CD-RW” />
<property name=”price” value=”1.5″ />
</bean>

<bean id=”dvdrw” class=”com.song.spring.scope.Disc”>
<property name=”name” value=”DVD-RW” />
<property name=”price” value=”3.0″ />
</bean>

<bean id=”shoppingCart” class=”com.song.spring.scope.ShoppingCart” />
</beans>

创建一个运行类：
[java] view plaincopyprint?
package com.song.spring.scope;

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

public class Main {

public static void main(String[] args) {

ApplicationContext context = new ClassPathXmlApplicationContext(“applicationContext.xml”);

Product aaa = (Product)context.getBean(“aaa”);
Product cdrw = (Product)context.getBean(“cdrw”);
Product dvdrw = (Product)context.getBean(“dvdrw”);

ShoppingCart cart1 = (ShoppingCart)context.getBean(“shoppingCart”);
cart1.addItem(aaa);
cart1.addItem(cdrw);
System.out.println(“Shopping Cart1 contains:” + cart1.getItem());

ShoppingCart cart2 = (ShoppingCart)context.getBean(“shoppingCart”);
cart2.addItem(dvdrw);
System.out.println(“Shopping Cart2 contains:” + cart2.getItem());
}

}
运行结果为：
Shopping Cart1 contains:[AAA 2.5, CD-RW 1.5]
Shopping Cart2 contains:[AAA 2.5, CD-RW 1.5, DVD-RW 3.0]
显然这不是我们想要的结果；我们所要的是每个顾客各获得一个Bean实例，这时就应该将配置文件中的Bean实例的作用域改为prototype;
[html] view plaincopyprint?
<bean id=”shoppingCart” class=”com.song.spring.scope.ShoppingCart” <span style=”color:#ff0000;”>scope=”prototype”</span>/>
再运行所得结果为：
Shopping Cart1 contains:[AAA 2.5, CD-RW 1.5]
Shopping Cart2 contains:[DVD-RW 3.0]
这才是我们想要的结果，完毕！