Bean的作用域

一共有6种，但是后面的四种是基于web应用的；

Scope Description
singleton (Default) Scopes a single bean definition to a single object instance for each Spring IoC container.
prototype Scopes a single bean definition to any number of object instances.
request Scopes a single bean definition to the lifecycle of a single HTTP request. That is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
application Scopes a single bean definition to the lifecycle of a ServletContext. Only valid in the context of a web-aware Spring ApplicationContext.
websocket Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext.

测试代码：

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ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext ("applicationContext.xml");
       Student student1 = (Student)context.getBean ("student");
       Student student2 = (Student)context.getBean ("student");
       System.out.println (student1==student2);

1.sigleton:无论创建几个都始终只有一个并且是默认的作用域

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<bean id="student" class="com.saxon.pojo.Student" c:name="saxon" scope="singleton">

结果：true

2.prototype:每次创建都会新建一个对象，就是浪费资源

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<bean id="student" class="com.saxon.pojo.Student" c:name="saxon" scope="prototype">

结果：false；

八、自动装配

1.显示自动装配 xml 装配

applicationContext.xml

2.Java文件自动装配

3.隐式自动装配

autowrite:

1.autowire=”byName”

它会自动寻找我们属性中还没有注入的属性，选取ID 为setXXX的XXX 自动装配

比如：

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public void setAddress (Address address) {
        this.address = address;
    }
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<bean id="address" class="com.saxon.pojo.Address">
        <property name="country" value="CHINA"/>
        <property name="province" value="YUNNAN"/>
 </bean>

这个的set后缀就是address，那么就去找ID为address的bean;如果ID不一致就不会自动装配；区分大小写,id唯一；

2.autowire=”byType”

会自动寻找我们属性中还没有注入的属性，选取类的类型为setXXX的XXX 自动装配

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public void setAddress (Address address) {
        this.address = address;
    }
//类就是address
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<bean id="address" class="com.saxon.pojo.Address">
        <property name="country" value="CHINA"/>
        <property name="province" value="YUNNAN"/>
 </bean>

com.saxon.pojo.Address类型唯一自动装配，于id无关；id可以不写；