ServletConfig & ServletContext 区别

最新推荐文章于 2025-09-07 01:02:55 发布

转载最新推荐文章于 2025-09-07 01:02:55 发布 · 101 阅读

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原文链接：https://my.oschina.net/u/3434392/blog/1498513

文章标签：

#web.xml #python #前端 #ViewUI

本文详细介绍了web.xml中的关键配置项，如<context-param>、<listener>和<servlet>等，解释了它们的作用及如何在Servlet容器中进行初始化。

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<context-param>

web.xml的配置项，标识application范围内的参数，加载比其他任何Servlet都早。

<listener>
	<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- Spring 刷新Introspector防止内存泄露 -->
<listener>
	<listener-class>org.springframework.web.util.IntrospectorCleanupListener</listener-class>
</listener>
<!-- c1-start 配置spring的父上下文 -->
<context-param>
	<param-name>contextConfigLocation</param-name>
	<param-value>classpath*:spring/spring.xml,classpath*:spring/applicationContext-per.xml
    </param-value>
</context-param>

<!-- 登录失败Url -->
<context-param>
	<param-name>failUrl</param-name>
	<param-value>/</param-value>
</context-param>

启动web容器将读取web.xml上的节点：<listener>、<context-param>；
容器将<context-param>转化成值对保存在web容器创建的application内共享的ServletContext中；

在ServletContextListener（ContextLoaderListener ）监听器中contextInitialized( ServletContextEvent sce ) 初始化方法中获得：
servletContext = ServletContextEvent.getServletContext()

	/** 
	 * Implementations of this interface receive notifications about
	 * changes to the servlet context of the web application they are
	 * part of.
	 * To receive notification events, the implementation class
	 * must be configured in the deployment descriptor for the web
	 * application.
	 * @see ServletContextEvent
	 * @since	v 2.3
	 */

public interface ServletContextListener extends EventListener {
	/**
	 ** Notification that the web application initialization
	 ** process is starting.
	 ** All ServletContextListeners are notified of context
	 ** initialization before any filter or servlet in the web
	 ** application is initialized.
	 */

    public void contextInitialized ( ServletContextEvent sce );

	/**
	 ** Notification that the servlet context is about to be shut down.
	 ** All servlets and filters have been destroy()ed before any
	 ** ServletContextListeners are notified of context
	 ** destruction.
	 */
    public void contextDestroyed ( ServletContextEvent sce );
}

ServletContext

WEB容器启动时会创建一个代表当前web应用的上下文ServletContext对象，通常称为context 域对象。
不同的Web应用，ServletContext各自独立存在。只在Web应用被关闭时才被销毁。

获取到整个web应用的配置信息<context-param>

 context-param的值 = ServletContext.getInitParameter("context-param的键");

实现Servlet间通讯。主要是4个有关 Attribute 的方法：setAttribute()、getAttribute()、removeAttribute()、getAttributeNames()

ServletContext context =this.getServletContext(); // servletContext域对象 
context.setAttribute("data","共享数据"); // 向域中存了一个data属性
// 在另一个servlet中，可以使用如下语句来获取域中的data属性
ServletContext context =this.getServletContext();
String value = (String)context.getAttribute("data");  // 获取域中的data属性

读取资源文件

String path= "/WEB-INF/classes/db.properties"; //默认'/webapp'下目录
//返回资源文件的读取字节流
InputStream in =this.getServletContext().getResourceAsStream(path);
//获得文件的完整绝对路径path，再使用字节流读取path下的文件
String allPath =this.getServletContext().getRealPath(path);
//获得一个url对象，调用该类的openStream方法返回一个字节流，读取数据
URL url=this.getServletContext().getResource(path);

<init-param>

servlet范围内的参数，只在指定的servlet中获取。

<!-- 配置springmvc的前端控制器,同时初始化子上下文 -->
<servlet>
	<servlet-name>springmvc</servlet-name>
	<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
	<init-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>classpath*:spring/spring-mvc.xml</param-value>
	</init-param>
	<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
	<servlet-name>springmvc</servlet-name>
	<url-pattern>/</url-pattern>
</servlet-mapping>

init-param的值 = Servlet.getInitParameter("init-param的键");