request,Session,Application,作用域经典案例

最新推荐文章于 2022-06-06 10:06:15 发布

weixin_44906154

最新推荐文章于 2022-06-06 10:06:15 发布

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本文链接：https://blog.youkuaiyun.com/weixin_44906154/article/details/90417028

此博客展示了一段Java代码，定义了一个名为AServlet的Servlet类。在service方法中，分别对request、Session和ServletContext对象中的计数变量进行操作。若变量为空则初始化为1，不为空则加1，体现了Servlet对不同作用域对象的使用。

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package cn.itsource._04num;

import java.io.IOException;

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 javax.servlet.http.HttpSession;
@WebServlet("/aser")
public class AServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//requet对象
Integer num_in_req=(Integer)req.getAttribute(“num_in_req”);
if(num_in_req == null){
req.setAttribute(“num_in_req”, 1);
}else{
req.setAttribute(“num_in_req”, num_in_req+1);
}
//Session对象
HttpSession session = req.getSession();
Integer num_in_session = (Integer)session.getAttribute(“num_in_session”);
if(num_in_sessionnull){
session.setAttribute(“num_in_session”,1);
}else{
session.setAttribute(“num_in_session”, num_in_session+1);
}
//Application --ServletContext对象
ServletContext servletContext = req.getServletContext();
Integer num_in_sc = (Integer)servletContext.getAttribute(“num_in_sc”);
if(num_in_scnull){
servletContext.setAttribute(“num_in_sc”, 1);
}else{
servletContext.setAttribute(“num_in_sc”, num_in_sc+1);
}

	 resp.setContentType("text/html;charset=utf-8");
	 //上面作用域对象设置了值,需要重新取一次
	 num_in_req=(Integer)req.getAttribute("num_in_req");
	 num_in_session = (Integer)session.getAttribute("num_in_session");
	 num_in_sc = (Integer)servletContext.getAttribute("num_in_sc");
	 
	 resp.getWriter().println("num_in_req:"+num_in_req+"<br/>");
	 resp.getWriter().println("num_in_session:"+num_in_session+"<br/>");
	 resp.getWriter().println("num_in_sc:"+num_in_sc+"<br/>");
}

}