1.概念：代表整个web应用（整个web工程），可以和程序的容器（服务器，例如：Tomcat）通信
2.获取
1.通过request对象获取：request.getServletContext();
2.通过HttpServlet获取：this.getServletContext();
package cn.itcast.web.servletcontext; 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; /** * @author 旗木五五开 * @create 2020-03-08 8:48 */ @WebServlet("/servletContextDemo1") public class ServletContextDemo1 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // servletContext获取 ServletContext context1 = request.getServletContext(); ServletContext context2 = this.getServletContext(); System.out.println(context1==context2);//true System.out.println(context1); System.out.println(context2); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }
3.功能：
1.获取MIE类型：在互联网通信过程中，定义的一种文件数据类型。（http协议也遵循这个类型的标准）
格式：大类型/小类型
例如：text/html：text表示纯文本，html表示内部是HTML形式的。html形式的纯文本
image/jpeg：图片/jpeg类型。jpeg类型的图片
用途：http协议响应头里有Content-Type: text/html;charset=UTF-8 设置文件的MIE类型，服务器告诉浏览器，响应体的格式，浏览器用相应的解析引擎去解析
获取：String getMimeType(String file);接收文件的名称（后缀名）返回一个string类型的值。
为什么能获取到，整个mime类型所有的对应关系都在服务器存储着，这个对象刚好可以服务器通信，所以可以获取到
package cn.itcast.web.servletcontext; 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; /** * @author 旗木五五开 * @create 2020-03-08 9:30 */ @WebServlet("/servletContextDemo2") public class ServletContextDemo2 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1.通过 HttpServlet 获取 ServletContext context = this.getServletContext(); // 2.定义文件名称。以后是通过对应的文件动态的获取 String filename="a.jpg"; // 3.获取mime类型 String mimeType = context.getMimeType(filename); System.out.println(mimeType); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }
2.域对象：共享数据
1.设置数的名称和值：setAttribute(String name,Object value);
2.通过名称获取对应的值：getAttribute(String name);
3.通过名称删除对应的值：removeAttribute(String name);
ServletContext对象范围：所有用户所有请求的数据
使用：要谨慎，所有用户都可以操作，不安全。而且对象的生命周期长，服务器启动就被创建了，服务器关了才能被销毁。对象驻留在内存能保持很久的时间。存储的数据多了会对内存产生压力
package cn.itcast.web.servletcontext; 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; /** * @author 旗木五五开 * @create 2020-03-08 9:45 */ @WebServlet("/servletContextDemo3") public class ServletContextDemo3 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1.通过 HttpServlet 获取 ServletContext context = this.getServletContext(); // 2.设置数据 context.setAttribute("msg","haha"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }
package cn.itcast.web.servletcontext; 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; /** * @author 旗木五五开 * @create 2020-03-08 9:47 */ @WebServlet("/servletContextDemo4") public class ServletContextDemo4 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1.通过 HttpServlet 获取 ServletContext context = this.getServletContext(); // 2.获取数据 Object msg = context.getAttribute("msg"); System.out.println(msg); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }
3.获取文件的真实（服务器）路径
方法：String getRealPath(String path); String path=/资源名.后缀
package cn.itcast.web.servletcontext; 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.File; import java.io.IOException; /** * @author 旗木五五开 * @create 2020-03-09 0:58 */ @WebServlet("/servletContextDemo5") public class ServletContextDemo5 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1.通过HttpServlet获取 ServletContext context = this.getServletContext(); // 2.获取文件的服务器路径 String b = context.getRealPath("/b.txt");//web目录下资源访问 System.out.println(b); String c = context.getRealPath("/WEB-INF/c.txt");//web-inf下的资源访问 System.out.println(c); String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问 System.out.println(a); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }
此目录就是：web目录下资源访问的路径。
有了路径就可以找到文件对应的目录找到后，就可以通过流，加载它进内存。
ClassLoader 类加载器：只能获取src下的目录不能获取web下的真实目录