9 ServletConfig和ServletContext

 ServletContext和ServletConfig

ServletContext对象

ServletContext对象介绍

ServletContext官方叫Servlet上下文。服务器会为每一个Web应用创建一个ServletContext对象。这个对象全局唯一，而且Web应用中的所有Servlet都共享这个对象。所以叫全局应用程序共享对象

 

 

ServletContext对象的作用

  Ø  相对路径转绝对路径

  Ø  获取容器的附加信息

  Ø  读取配置信息

  Ø  全局容器

 

    

ServletContext对象的使用

获取项目的部署名 context.getContextPath() 相对路径转绝对路径(文件上传下载时需要注意)

context.getRealPath("path")

该方法可以将一个相对路径转换为绝对路径，在文件上传与下载时需要用到该方法做路径的转换。

获取容器的附加信息

servletContext.getServerInfo()

返回Servlet容器的名称和版本号

servletContext.getMajorVersion()

返回Servlet容器所支持Servlet的主版本号

servletContext.getMinorVersion()

返回Servlet容器所支持Servlet的副版本号。

获取web.xml文件中的信息

<context-param> <param-name>key</param-name> <param-value>value</param-value> </context-param>

 

servletContext.getInitParameter("key") 该方法可以读取web.xml文件中<context-param>标签中的配置信息。

servletContext.getInitParameterNames()

该方法可以读取web.xml文件中所有param-name标签中的值。

全局容器

servletContext.setAttribute("key",ObjectValue)

向全局容器中存放数据。

servletContext.getAttribute("key")

从全局容器中获取数据。

servletContext.removeAttribute("key")

根据key删除全局容器中的value。

ServletContext对象生命周期

当容器启动时会创建ServletContext对象并一直缓存该对象，直到容器关闭后该对象生命周期结束。ServletContext对象的生命周期非常长，所以在使用全局容器时不建议存放业务数据。

ServletConfig对象

ServletConfig对象对应web.xml文件中的<servlet>节点。当Tomcat初始化一个Servlet时，会将该Servlet的配置信息，封装到一个ServletConfig对象中。我们可以通过该对象读取<servlet>节点中的配置信息

<servlet> <servlet-name>servletName</servlet-name> <servlet-class>servletClass</servlet-class> <init-param> <param-name>key</param-name> <param-value>value</param-value> </init-param> </servlet>

 

servletConfig.getInitParameter("key");

该方法可以读取web.xml文件中<servlet>标签中<init-param>标签中的配置信息。

servletConfig.getInitParameterNames();

该方法可以读取web.xml文件中当前<servlet>标签中所有<init-param>标签中的值。

测试代码

Servlet1

 

package com.msb.testServlet;import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.util.ArrayList; import java.util.Collections; import java.util.List; /** * @Author: Ma HaiYang * @Description: MircoMessage:Mark_7001 */ public class Servlet1 extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //获取Servlet对象的方式 // 通过req对象 ServletContext servletContext1 = req.getServletContext(); // 通过继承的方法 ServletContext servletContext2 = this.getServletContext(); System.out.println(servletContext1 == servletContext2); // 获取当前项目的部署名 String contextPath = servletContext1.getContextPath(); System.out.println("contextPath"+contextPath); // 将一个相对路径转化为项目的绝对路径 String fileUpload = servletContext1.getRealPath("fileUpload"); System.out.println(fileUpload); String serverInfo = servletContext1.getServerInfo(); System.out.println("servletInfo"+serverInfo); int majorVersion = servletContext1.getMajorVersion(); int minorVersion = servletContext1.getMinorVersion(); System.out.println(majorVersion+":"+minorVersion); // 获取web.xml中配置的全局的初始信息 String username = servletContext1.getInitParameter("username"); String password = servletContext1.getInitParameter("password"); System.out.println(username+":"+password); //向ServletContext对象中增加数据 域对象 List<String> data=new ArrayList<>(); Collections.addAll(data,"张三","李四","王五"); servletContext1.setAttribute("list",data); servletContext1.setAttribute("gender","boy"); } }

 

 

Servlet2

package com.msb.testServlet;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.util.Enumeration;import java.util.List;/** * @Author: Ma HaiYang * @Description: MircoMessage:Mark_7001 */public class Servlet2 extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext servletContext = this.getServletContext(); // 获取web.xml中配置的全局的初始信息 Enumeration<String> pnames = servletContext.getInitParameterNames(); while(pnames.hasMoreElements()){ String e = pnames.nextElement(); System.out.println(e+":"+servletContext.getInitParameter(e)); } List<String> list = (List<String>) servletContext.getAttribute("list"); System.out.println(list); String gender = (String)servletContext.getAttribute("gender"); System.out.println(gender); }}

 

Servlet3

package com.msb.testServlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/** * @Author: Ma HaiYang * @Description: MircoMessage:Mark_7001 */public class Servlet3 extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletConfig servletConfig = this.getServletConfig(); System.out.println(servletConfig.getInitParameter("brand")); System.out.println(servletConfig.getInitParameter("screen")); }}

 

Servlet4

package com.msb.testServlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/** * @Author: Ma HaiYang * @Description: MircoMessage:Mark_7001 */public class Servlet4 extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletConfig servletConfig = this.getServletConfig(); System.out.println(servletConfig.getInitParameter("pinpai")); System.out.println(servletConfig.getInitParameter("pingmu")); }}

 

web.xml配置

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> <context-param> <param-name>username</param-name> <param-value>mashibing</param-value> </context-param> <context-param> <param-name>password</param-name> <param-value>123456</param-value> </context-param> <servlet> <servlet-name>servlet1</servlet-name> <servlet-class>com.msb.testServlet.Servlet1</servlet-class> </servlet> <servlet> <servlet-name>servlet2</servlet-name> <servlet-class>com.msb.testServlet.Servlet2</servlet-class> </servlet> <servlet> <servlet-name>servlet3</servlet-name> <servlet-class>com.msb.testServlet.Servlet3</servlet-class> <init-param> <param-name>brand</param-name> <param-value>ASUS</param-value> </init-param> <init-param> <param-name>screen</param-name> <param-value>三星</param-value> </init-param> </servlet> <servlet> <servlet-name>servlet4</servlet-name> <servlet-class>com.msb.testServlet.Servlet4</servlet-class> <init-param> <param-name>pinpai</param-name> <param-value>联想</param-value> </init-param> <init-param> <param-name>pingmu</param-name> <param-value>京东方</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>servlet1</servlet-name> <url-pattern>/servlet1.do</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>servlet2</servlet-name> <url-pattern>/servlet2.do</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>servlet3</servlet-name> <url-pattern>/servlet3.do</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>servlet4</servlet-name> <url-pattern>/servlet4.do</url-pattern> </servlet-mapping> </web-app>