Java RequestDispatcher 详解

RequestDispatcher 让两个servlet相互通信成为可能，就像是浏览器发送request请求一样。所以我们可以从HttpRequest中获取到RequestDispatcher对象

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

  RequestDispatcher dispatcher=request.getRequestDispatcher("/servlet2");
}

通过上面的代码，我们能获取到一个映射到/servlet2（URI）的Servlet的 RequestDispatcher。

然后可以使用include()或者forward()方法来调用RequestDispatcher

dispatcher.forward(request, response);

dispatcher.include(request, response);

标题 request.getRequestDispatcher和response.sendRedirct区别

getRequestDispatcher是服务器内部跳转，地址栏信息不变，只能跳转到web应用内的网页。
sendRedirect是页面重定向，地址栏信息改变，可以跳转到任意网页。

getRequestDispatcher实例

   request.setAttribute("lover", "fantj");  
   request.getSession().setAttribute("lovered", "fantj");  
  
   request.getRequestDispatcher("/third?name=fantj").forward(request, response);  
   或  
   request.getRequestDispatcher("third?name=fantj").forward(request, response);  
   或  
   this.getServletContext().getRequestDispatcher("/third?name=fantj").forward(request, response);

//ThirdServlet  
   PrintWriter out = response.getWriter();  
   String name = request.getParameter("name");  
   out.println(request.getContextPath()+"<hr/>");  
   out.println("name="+name+"<hr/>");  
   out.println("lover="+request.getAttribute("lover")+"<hr/>");  
   out.println("lovered="+request.getSession().getAttribute("lovered")+"<hr/>");