servlet中的ServletContext

设置、获取ServletContext配置信息

与ServletConfig不同的是，所有Servlet共享一份ServletContext

1. 在web.xml中设置配置信息

   <?xml version="1.0" encoding="UTF-8"?>
   <web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd"version="6.0"><context-param><param-name>key1</param-name><param-value>a</param-value></context-param><context-param><param-name>key2</param-name><param-value>b</param-value></context-param>
   </web-app>
   

2. 在service方法中读取

   public class ServletTest extends HttpServlet {public void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext servletContext = this.getServletContext();// 获取指定的配置信息String value = servletContext.getInitParameter("key2");System.out.println(value);// 批量获取配置信息Enumeration<String> initParameterNames = servletContext.getInitParameterNames();while(initParameterNames.hasMoreElements()) {String key = initParameterNames.nextElement();System.out.println(key + "=" + servletContext.getInitParameter(key));}}
   } 
   

通过ServletContext获取项目实际部署的根路径：getRealPath()

ServletContext servletContext = this.getServletContext();
// 获取项目实际部署的根路径(绝对路径)
String rootPath = servletContext.getRealPath(""); // D:\workspace\javawebproject\out\artifacts\demo1_war_exploded\
// 获取项目实际部署的根目录下的static路径（绝对路径）
String staticPath = servletContext.getRealPath("static"); // D:\workspace\javawebproject\out\artifacts\demo1_war_exploded\static

通过ServletContext获取项目的访问路径：getContextPath()

ServletContext servletContext = this.getServletContext();
// 获取项目的访问路径
String accessPath = servletContext.getContextPath(); // /demo1

域对象

ServletContext是应用域，作用于整个应用，所有Servlet都可访问到，可用于存储和传递数据，实现各个Servlet之间的通信

在servlet1中存储数据，供Servlet2获取

// Servlet1
public class Servlet1 extends HttpServlet {public void service(HttpServletRequest req, HttpServletResponse resp) {// 在servlet1中存储数据，供Servlet2获取ServletContext servletContext = this.getServletContext();servletContext.setAttribute("aaa", 123);}
}
// Servlet2
public class Servlet2 extends HttpServlet {public void service(HttpServletRequest req, HttpServletResponse resp) {// 供Servlet2中获取ServletContext servletContext = this.getServletContext();String value = (String) servletContext.getAttribute("aaa");System.out.println(value);// 移除数据servletContext.removeAttribute("aaa");}
}