学习博客：【JavaWeb】ServletContext

web容器在启动时，为每个web程序创建一个对应的ServletContext对象，代表当前的web应用

共享数据：在一个Servlet中保存的数据，在另一个Servlet中拿到

package com.yl.servlet;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //this.getInitParameter();      初始化参数
        //this.getServletConfig();      Servlet配置
        //this.getServletContext();     Servlet上下
        ServletContext context = this.getServletContext();

        String username = "杨杨";
        context.setAttribute("username", username);     //将数据保存在ServletContext中
        
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

package com.yl.servlet;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;

public class GetServlet extends HelloServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {


        ServletContext context = this.getServletContext();
        String username = (String)context.getAttribute("username");

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        PrintWriter writer = resp.getWriter();
        writer.print("名字：" + username);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

web.xml

    
    
    
        hello
        com.yl.servlet.HelloServlet
    
    
    
        hello
        /hello
    

    
        getc
        com.yl.servlet.GetServlet
    

    
        getc
        /get
    

    url
    jdbc:mysql://localhost:3306/mybatis

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    ServletContext context = this.getServletContext();

    String url = context.getInitParameter("url");
    resp.getWriter().println(url);
}

Properties

• java目录下新建properties
• resources目录下新建properties

都被打包到同一路径下 classes 称为classpath

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    //InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
    InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/yl/servlet/aa.properties");

    Properties prop = new Properties();
    prop.load(is);
    String un = prop.getProperty("username");
    String pwd = prop.getProperty("password");

    resp.getWriter().print(un + ":" + pwd);
}

    sd5
    com.yl.servlet.ServletDemo05



    sd5
    /sd5