Servlet--Request2

最新推荐文章于 2024-10-18 16:11:46 发布

原创最新推荐文章于 2024-10-18 16:11:46 发布 · 182 阅读

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本文深入探讨了Servlet中的请求转发和请求包含技术，详细讲解了RequestDispatcher的作用及其实现方式，包括forward方法和include方法的区别与应用。通过实例演示了如何在Servlet之间共享数据，并在JSP页面中展示转发过来的数据。

request功能

请求转发–资源跳转

在多个资源之间共享数据，在浏览器看来依然是demo4给的资源，一次请求，一次响应
内部跳转，浏览器感知不到—地址栏不会发生变化
requestDispatcher 调度器
forward 请求转发，请求对象和响应对象转发到下一个资源
同一个Servlet不可以多次请求转发，请求转发前后的代码可以正常执行。
demo4

@WebServlet("/RequestDemo4")
public class RequestDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         //创建调度器
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/RequestDemo5");
        //请求转发之前 会清空缓冲区
        //response.getWriter().write("this is demo4");
       // response.flushBuffer();异常 强行冲刷会造成一次响应，一次请求只对应一次响应。
        //利用调度器实现转发
        requestDispatcher.forward(request,response);
        //同一个Servlet中不能多次请求和转发
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

demo5

@WebServlet("/RequestDemo5")
public class RequestDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //RequestDispatcher requestDispatcher = request.getRequestDispatcher("/RequestDemo6");
        //requestDispatcher.forward(request,response);
       response.getWriter().write("this is demo5");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

地址栏没有发生变化
在这里插入图片描述

多重转发—请求链

在这里插入图片描述
demo5

 request.getRequestDispatcher("/RequestDemo6").forward(request,response);

demo6

@WebServlet("/RequestDemo6")
public class RequestDemo6 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().write("this is demo6");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

在这里插入图片描述

作为域对象使用

希望在请求转发的过程中，共享一些数据，这些数据可以通过域对象共享。
域对象：如果一个对象有一个可以看见的范围，这个范围内利用对象身上的map实现数据共享，这个对象就可以称之为域对象。

可以在一个范围内共享数据，request就是这样一个域对象，在请求转发之后，可以把所有数据共享使用。

demo7与demo8共享

setAttribute 向域中添加新数据
getAttribute 获取指定名称的域属性
removeAttribute 删除域属性
getAttributeNames 获取所有域属性的名称

demo7

@WebServlet("/RequestDemo7")
public class RequestDemo7 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //向域中添加新数据
        request.setAttribute("name","张德帅");
        //请求转发
        request.getRequestDispatcher("/RequestDemo8").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

demo8

报错处理快捷键 alt+回车

@WebServlet("/RequestDemo8")
public class RequestDemo8 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取指定名称的域属性
        String name = (String) request.getAttribute("name");
        System.out.println("name"+name);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

浏览器什么输出也没有
实际上 demo7是域，写入数据后，demo8从里·取出数据输出到控制台

利用域对象与index.jsp共享数据

设置域属性

@WebServlet("/RequestDemo9")
public class RequestDemo9 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //设置域属性
        request.setAttribute("name","张迦南大帅比");
        request.setAttribute("age","18");
        request.setAttribute("addr","伊拉克");
        request.setAttribute("gender","男");
        //请求转发--index.jsp
        request.getRequestDispatcher("/index.jsp").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

jsp 允许java语句的html页面

<%=具有返回值的Java表达式%>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
  <h3> 大王叫我来巡山喽 获取demo9的数据</h3>
  姓名:<%=request.getAttribute("name")%><br/>
  性别:<%=request.getAttribute("gender")%><br/>
  年龄:<%=request.getAttribute("age")%><br/>
  地址:<%=request.getAttribute("addr")%><br/>
  </body>
</html>

在这里插入图片描述

请求包含资源服务器内部合并浏览器不知道

合并多个资源的输出结果，再响应给浏览器的请求方式。

@WebServlet("/RequestDemo10")
public class RequestDemo10 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/RequestDemo11");
        response.getWriter().write("how are you  ");
        requestDispatcher.include(request,response);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

@WebServlet("/RequestDemo11")
public class RequestDemo11 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.getWriter().write("how old are you");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}