Application Context Webapplicationcontext

First, say ServletContext

The Java EE standard specifies that the servlet container needs to initialize a servletcontext as a public environment container for public information when the application project starts. The information in the ServletContext is provided by the container.

Example:

Get the parameters configured in Web. XML by customizing Contextlistener 1. When the container starts, locate the Context-param in the configuration file as the key-value pair in ServletContext 2. Then find the listener, the container calls its contextinitial Ized (Servletcontextevent Event) method, perform one of the following actions, such as: Configuring in Web. xml

<context-param>   <param-name>key</param-name>   <param-value>value123</ Param-value></context-param><listener>    <listener-class> Com.brolanda.contextlistener.listener.contextlistenertest</listener-class></listener>

Once configured, get the corresponding parameter information in the class

Package Com.brolanda.contextlistener.listener;import Javax.servlet.servletcontext;import Javax.servlet.servletcontextevent;import Javax.servlet.servletcontextlistener;public class ContextListenerTest Implements Servletcontextlistener {public        void contextdestroyed (Servletcontextevent event) {        System.out.println ("*************destroy contextlistener*************");    }        @SuppressWarnings ("unused") public    void Contextinitialized (Servletcontextevent event) {        System.out.println ("*************init contextlistener*************");        ServletContext ServletContext = Event.getservletcontext ();        System.out.println ("Key:" +servletcontext.getinitparameter ("key"));    }    }

Execution process:

Web. XML declares application-scoped initialization parameters in the <context-param></context-param> tag

1. When you start a Web project, the container (for example, Tomcat) reads its configuration file, Web. Read two nodes: <listener></listener> and <context-param></ Context-param>2. Immediately thereafter, the container creates a ServletContext (context). Globally shared within the app.

3. The container converts <context-param></context-param> into a key-value pair and gives it to ServletContext.

4. The container creates a class instance in <listener></listener>, that is, the listener is created. The listener must implement a self-servletcontextlistener interface

5. Contextinitialized (Servletcontextevent Event) initialization method in listening

Get ServletContext = Servletcontextevent.getservletcontext () in this method;
            "Context-param value" = Servletcontext.getinitparameter ("Context-param key"); 6. After you get the value of this context-param, you can do something about it. Note that this time your Web project is not fully started yet. This action will be earlier than all servlets. In other words, at this time, you have a <context-param> The key values in the operation will be executed before your Web project is fully started.   web.xml can define two parameters:    One is the global parameter (ServletContext), through the < context-param></context-param>    One is the servlet parameter, by declaring      <init-param in the servlet >                                                           ,         &N Bsp     <param-name>param1</param-name>                  & nbsp                          ,         &NB Sp                  <param-value>avalible in servlet init () </param-value>                                    ,         &NB Sp                         </init-param>      The first parameter in the servlet can be obtained by Getservletcontext (). Getinitparameter ("Context/param")      The second parameter can only be obtained by This.getinitparameter ("param1") in the servlet's init () method  

Second, Spring context container configuration

Spring provides us with a context-initialization listener that implements the Servletcontextlistener interface: Org.springframework.web.context.ContextLoaderListener

Spring provides us with an IOC container that requires us to specify the container's configuration file, which is then initialized and created by the listener. Requires you to specify the address and file name of the configuration file, be sure to use: Contextconfiglocation as the parameter name.

<context-param>    <param-name>contextConfigLocation</param-name>    <param-value>/ web-inf/applicationcontext.xml,/web-inf/action-servlet.xml,/web-inf/jason-servlet.xml</param-value></ Context-param><listener>    <listener-class> Org.springframework.web.context.contextloaderlistener</listener-class></listener>

The listener, by default, reads the Applicationcontext.xml file under/web-inf/. However, after specifying the configuration file path through Context-param, the corresponding configuration file is read and initialized under the path you specify.

Iii. what is initialized after the spring context container is configured?

Now that ServletContext was initialized by the servlet container, what did spring Contextloaderlistener do to initialize it?

1, the servlet container starts, creates a "global context" for the application: ServletContext 2, The container invokes the Contextloaderlistener configured in Web. XML, initializes the Webapplicationcontext context (that is, the IOC container), loads the Context-param specified profile information into the IOC container. Webapplicationcontext is stored as a key-value pair in the ServletContext 3, The container initializes the servlet configured in Web. XML, initializes its own context information servletcontext, and loads the configuration information for its settings into that context.        Sets the Webapplicationcontext to its parent container. 4. All subsequent servlet initializations are created in 3 steps, initializing their own context and setting Webapplicationcontext to their parent context.

For the scope, the contents of the ApplicationContext created by Contextloaderlistener can be referenced in Dispatcherservlet, but not in the reverse. When spring executes ApplicationContext's Getbean, it is found in the parent applicationcontext if the corresponding bean is not found in its own context. This also explains why we can get the beans in the dispatcherservlet that correspond to the ApplicationContext in the Contextloaderlistener.

  Four, spring configuration, the use of:<context:exclude-filter> reasons, Why the controller is excluded from Applicationcontext.xml, and incloud the controller

in Spring-mvc.xml

Now that you know the spring START process, the Web container initializes the Webapplicationcontext as a public context, only the configuration information for service, DAO, and so on is loaded here, and the servlet's own contextual information does not need to be loaded. Therefore, the components of the @controller annotation are excluded from the applicationcontext.xml, and the components of the @controller annotation are loaded in the Dispatcherservlet loaded configuration file. Easy to Dispatcherservlet control and find. Therefore, the configuration is as follows: APPLICATIONCONTEXT.MXL: <context:component-scan base-package= "Com.linkage.edumanage" > <context: Exclude-filter expression= "Org.springframework.stereotype.Controller" type= "annotation"/> </context:   Component-scan> spring-mvc.xml: <context:component-scan base-package= "Com.brolanda.cloud" Use-default-filters= "false" > <context:include-filter expression= "Org.springframework.stereotype.Controller "Type=" annotation "/> </context:component-scan>

Application Context Webapplicationcontext