Spring Bean Scope (做用域)

singleton:

單例模式，針對每一個spring容器，只有一個該類的實例被管理，每次調用此實例都是同一個對象被返回，因此適用於無狀態bean。默認狀況下，singleton做爲spring容器中bean的做用域。

<bean id="accountService" class="com.foo.DefaultAccountService"/>

<!-- the following is equivalent, though redundant (singleton scope is the default); using spring-beans-2.0.dtd -->
<bean id="accountService" class="com.foo.DefaultAccountService" scope="singleton"/>

<!-- the following is equivalent and preserved for backward compatibility in spring-beans.dtd -->
<bean id="accountService" class="com.foo.DefaultAccountService" singleton="true"/>

prototype:

針對每一次bean調用，注入或者程序中顯式調用getBean(...)相似方法，都有一個新的對象被初始化後返回，因此適用於有狀態bean。值得注意的是儘管初始化回調方法依然會被調用，可是聲明爲prototype的bean的「銷燬」回調方法不會被容器調用。spring container初始裝配以後將控制權交給客戶代碼，客戶代碼須要承擔釋放資源的責任。（spring 提供prototype資源的釋放方案，BeanPostProcessors）。

<!-- using spring-beans-2.0.dtd -->
<bean id="accountService" class="com.foo.DefaultAccountService" scope="prototype"/>

<!-- the following is equivalent and preserved for backward compatibility in spring-beans.dtd -->
<bean id="accountService" class="com.foo.DefaultAccountService" singleton="false"/>

request，session，global session:

以上三種顧名思義，做用域分別是http request級別，session級別。spring context須要是web實現（好比：XmlWebApplicationContext）。DispatcherServlet/DispatcherPortlet，RequestContextListener 或RequestContextFilter 負責將每一個http request/session 綁定到負責相應這個請求的線程上，並使得聲名爲request/session做用域的bean在後續調用中可用。

spring mvc

<servlet>
        <servlet-name>rest</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

servlet 2.4+

<web-app>
  ...
  <listener>
    <listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>
  </listener>
  ...
</web-app>

servlet 2.3

<web-app>
  ..
  <filter> 
    <filter-name>requestContextFilter</filter-name> 
    <filter-class>org.springframework.web.filter.RequestContextFilter</filter-class>
  </filter> 
  <filter-mapping> 
    <filter-name>requestContextFilter</filter-name> 
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  ...
</web-app>

 

refer to spring reference