singleton:
单例模式，针对每个spring容器，只有一个该类的实例被管理，每次调用此实例都是同一个对象被返回，所以适用于无状态bean。默认情况下，singleton作为spring容器中bean的作用域。
<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:
针对每一次bean调用，注入或者程序中显式调用getBean(...)类似方法，都有一个新的对象被初始化后返回，所以适用于有状态bean。值得注意的是尽管初始化回调方法依然会被调用，但是声明为prototype的bean的“销毁”回调方法不会被容器调用。spring container初始装配之后将控制权交给客户代码，客户代码需要承担释放资源的责任。（spring 提供prototype资源的释放方案，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:
以上三种顾名思义，作用域分别是http request级别，session级别。spring context需要是web实现（比如：XmlWebApplicationContext）。DispatcherServlet/DispatcherPortlet，RequestContextListener 或RequestContextFilter 负责将每个http request/session 绑定到负责相应这个请求的线程上，并使得声名为request/session作用域的bean在后续调用中可用。
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