什么是ServletContext？

根據(jù)字面意思即Servlet上下文

服務(wù)器會(huì)為每一個(gè)工程創(chuàng)建一個(gè)對(duì)象，這個(gè)對(duì)象就是ServletContext對(duì)象，這個(gè)對(duì)象是全局唯一的，工程內(nèi)部的所有servlet都共享這個(gè)對(duì)象，所有應(yīng)用程序共享對(duì)象

下面用一段簡(jiǎn)單的代碼來證明一下

import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet('/ServletContext2')public class ServletContext2 extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext servletContext = this.getServletContext(); System.out.println('ServletContext2的地址：'); System.out.println(servletContext); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doGet(req, resp); }}

import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet('/ServletContext')public class ServletContext extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { javax.servlet.ServletContext servletContext = this.getServletContext(); System.out.println('ServletContext2的地址：'); System.out.println(servletContext); RequestDispatcher servletContext2 = req.getRequestDispatcher('ServletContext2'); servletContext2.forward(req,resp); }}

可以看到二者的地址一模一樣

ServletContext對(duì)象的生命周期

誕生：web部署到服務(wù)器上，啟動(dòng)服務(wù)器，此時(shí)上下文環(huán)境對(duì)象創(chuàng)建，只要tomcat服務(wù)器不關(guān)閉，上下文環(huán)境對(duì)象就一直存在

銷毀：關(guān)閉服務(wù)器或者是從web服務(wù)器上卸載該程序的時(shí)候，該對(duì)象銷毀

怎么創(chuàng)建ServletContext對(duì)象？

方法一：

javax.servlet.ServletContext servletContext = this.getServletContext();

方法二:

javax.servlet.ServletContext servletContext1 = req.getServletContext();

方法三：

javax.servlet.ServletContext servletContext3 = this.getServletConfig().getServletContext();

ServletContext對(duì)象的作用與相關(guān)方法

1.是一個(gè)域?qū)ο?

什么是域：域其實(shí)就是一個(gè)map結(jié)構(gòu)，及存入一個(gè)鍵值對(duì)，來存儲(chǔ)獲取數(shù)據(jù)作用范圍：本工程內(nèi)部域?qū)ο罂梢员槐竟こ虄?nèi)所有的servlet對(duì)象共享，因?yàn)橐粋€(gè)工程只有一個(gè)servletcontext對(duì)象

方法介紹：存儲(chǔ)數(shù)據(jù)： void setAttribute(String var1, Object var2);

移除數(shù)據(jù)： void removeAttribute(String var1);

獲取數(shù)據(jù)： Object getAttribute(String var1);1.由于取出的是一個(gè)Object類型，需要強(qiáng)轉(zhuǎn)2.如果指定的屬性名不存在，則返回null

2.可以獲取文件的真實(shí)路徑

真實(shí)路徑：即部署在服務(wù)器是的路徑String getRealPath（） 獲取文件的真實(shí)路徑

不同目錄下訪問資源的方式不同

//src下的資源訪問 String realPath = servletContext.getRealPath('/WEB-INF/classes/a.text'); System.out.println(realPath);//WEB-INF下的資源訪問 String realPath1 = servletContext.getRealPath('/WEB-INF/b.text'); System.out.println(realPath1); //web目錄下的資源訪問 String realPath2 = servletContext.getRealPath('/c.text'); System.out.println(realPath2);

代碼

import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet('/ServletContext')public class ServletContext extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { javax.servlet.ServletContext servletContext = this.getServletContext(); //src下的資源訪問 String realPath = servletContext.getRealPath('/WEB-INF/classes/a.text'); System.out.println(realPath); //WEB-INF下的資源訪問 String realPath1 = servletContext.getRealPath('/WEB-INF/b.text'); System.out.println(realPath1); //web目錄下的資源訪問 String realPath2 = servletContext.getRealPath('/c.text'); System.out.println(realPath2); }}

結(jié)果

3.獲得MIME類型

s什么是MIME類型，是在互聯(lián)網(wǎng)通信過程中定義等等一種文件數(shù)據(jù)類型格式：大類型/小類型 image/jpeg獲?。?String getMimeType（String file)

代碼如下

import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet('/ServletContext')public class ServletContext extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { javax.servlet.ServletContext servletContext = this.getServletContext(); String filename='a.jpg'; String mimeType = servletContext.getMimeType(filename); System.out.println(mimeType); }}

結(jié)果

以上就是ServletContext對(duì)象的一些基礎(chǔ)知識(shí)，如有錯(cuò)誤還請(qǐng)各位批評(píng)指正，喜歡我的文章可以點(diǎn)贊呀，也可以關(guān)注我，我會(huì)經(jīng)常跟新文章

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