JavaWeb ServletContext基础与应用详细讲解

// 第一种方式
ServletContext app1 = config.getServletContext();
writer.println("<br>" + app1);
// 第二种方式
ServletContext app2 = this.getServletContext();
writer.println("<br>" + app2);

<?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_5_0.xsd"
         version="5.0">
    <!-- 定义了两个外部参数 -->
    <context-param>
        <param-name>pageSize</param-name>
        <param-value>10</param-value>
    </context-param>
    <context-param>
        <param-name>porkPrice</param-name>
        <param-value>999</param-value>
    </context-param>
    ...
</web-app>

package com.zhiyiyi.javaweb.servlet;
import jakarta.servlet.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
public class AServlet extends GenericServlet {
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        servletResponse.setContentType("text/html");
        PrintWriter writer = servletResponse.getWriter();
        ServletContext servletContext = this.getServletContext();
        // 迭代输出param-name和param-value
        Enumeration<String> initParameterNames = servletContext.getInitParameterNames();
        while (initParameterNames.hasMoreElements()) {
            String key = initParameterNames.nextElement();
            String value = servletContext.getInitParameter(key);
            writer.println(key + " " + value + "<br>");
        }
    }
}

// 获取web的根路径
String contextPath = servletContext.getContextPath();
writer.println("<br>" + contextPath);

// 获取绝对路径
String realPath = servletContext.getRealPath("/index.html");
writer.println("<br>" + realPath);

// 以键值对的方式添加参数
servletContext.setAttribute("name","tom");
// 获取参数
Object name = servletContext.getAttribute("name");
// 删除参数
servletContext.removeAttribute("name");