把spring集成到web框架很简单，只要在web.xml里面加上
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/applicationContext*.xml</param-value>
</context-param>
或者
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
如果为下面这种方式的话，那么就是加载默认的文件
/WEB-INF/applicationContext.xml
这个在
org.springframework.web.context.support.XmlWebApplicationContext类里面定义的,,部分代码：
/** Default config location for the root context */
public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";
/** Default prefix for building a config location for a namespace */
public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";
/** Default suffix for building a config location for a namespace */
public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";
Once the context files are loaded, Spring creates a WebApplicationContext object based on the bean definitions and puts it into the ServletContext.
这样我们就可以直接用ServletContext获取自己想要的参数的，，
All Java web frameworks are built on top of the Servlet API, so you can use the following code to get the ApplicationContext that Spring created.
WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);
通过WebApplicationContext我们就可以通过bean的名字获取它的实例了
The WebApplicationContextUtils class is for convenience, so you don't have to remember the name of the ServletContext attribute. Its getWebApplicationContext() method will return null if an object doesn't exist under the WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE key. Rather than risk getting NullPointerExceptions in your application, it's better to use the getRequiredWebApplicationContext() method. This method throws an Exception when the ApplicationContext is missing.
Once you have a reference to the WebApplicationContext, you can retrieve beans by their name or type. Most developers retrieve beans by name, then cast them to one of their implemented interfaces.
Fortunately, most of the frameworks in this section have simpler ways of looking up beans. Not only do they make it easy to get beans from the BeanFactory, but they also allow you to use dependency injection on their controllers. Each framework section has more detail on its specific integration strategies.