Servlet中的请求转发和重定向

Posted 2020-08-08 kuillldan

跳转和重定向

有的时候客户端请求到达服务端后需要对请求重新转发到其它Servlet甚至别的服务器，这就需要跳转和重定向。

区别

一般来说，跳转是服务器内部跳转，例如将请求从一个Servlet转发给另外一个Servlet处理，是内部之间的转发。而重定向是告诉客户端去别的地方请求资源。举个例子，某人需要去找人事部门打印收入证明，而收入证明需要去财务部盖章。跳转的处理方式是：人事部门的人告诉你，你等一下，我去把收入证明打印出来，然后我再去找财务部盖章，所有资料准备好后，我再全部交给你。重定向的处理方式是：人事部门把收入流水给你打印出来，然后告诉你说，他们的工作已经做完了，现在需要你自己去找财务部盖章。

这就是跳转和重定向的本质区别，服务器跳转的时候，客户端地址栏不改变，而客户端重定向的时候，地址栏改变。

跳转示例

跳转需要用到RequestDispacher对象，该对象可以从HttpRequest或者ServletContext中获取。

下面是从HttpRequest对象中调用getRequestDispacher()方法获取RequestDispacher并跳转示例代码：

protected void doPost(HttpServletRequest req, HttpServletResponse resp) {         RequestDispatcher rd = null;        String region = req.getParameter("region");        System.out.println("region: " + region);        switch (region)        {               case "asia":               {                      System.out.println("asia~~~");                      rd = req.getRequestDispatcher("/asiaHandler.jsp");                      break;               }               case "emea":               {                      System.out.println("emea~~~");                      rd = req.getRequestDispatcher("/emeaHandler.jsp");                      break;               }               case "ams":               {                      System.out.println("ams~~~");                      rd = req.getRequestDispatcher("/amsHandler.jsp");                      break;               }               default:               {                      System.out.println("default~~~");                      rd = req.getRequestDispatcher("/html/error.html");                      break;               }        }               try        {               rd.forward(req, resp);        } catch (ServletException | IOException e)        {               // TODO Auto-generated catch block               e.printStackTrace();        }               }

 

下面是从ServletContext对象中调用getNamedDispacher()方法获取RequestDispacher对象并跳转示例代码:

protected void doPost(HttpServletRequest req, HttpServletResponse resp) {         RequestDispatcher rd = null;        ServletContext ctx = this.getServletContext();        String region = req.getParameter("region");        System.out.println("region: " + region);        switch (region)        {               case "asia":               {                      rd = ctx.getNamedDispatcher("AsiaHandler");                      break;               }               case "emea":               {                      rd = ctx.getNamedDispatcher("EmeaHandler");                      break;               }               case "ams":               {                      rd = ctx.getNamedDispatcher("AMSHandler");                      break;               }        }               try        {               rd.forward(req, resp);        } catch (ServletException | IOException e)        {               // TODO Auto-generated catch block               e.printStackTrace();        } }

 

下面演示了用ServletContext对象调用getRequestDispacher()方法获取RequestDispacher对象，然后实现跳转:

protected void doPost(HttpServletRequest req, HttpServletResponse resp) {         RequestDispatcher rd = null;        ServletContext ctx = this.getServletContext();        String region = req.getParameter("region");        System.out.println("region: " + region);        switch (region)        {               case "asia":               {                      rd = req.getRequestDispatcher("/asiaHandler.jsp");                      break;               }               case "emea":               {                      rd = req.getRequestDispatcher("/emeaHandler.jsp");                      break;               }               case "ams":               {                      rd = req.getRequestDispatcher("/amsHandler.jsp");                      break;               }          }               try        {               rd.forward(req, resp);        } catch (ServletException | IOException e)        {               // TODO Auto-generated catch block               e.printStackTrace();        } }

 

请求重定向是服务器发给浏览器一个新的地址，让浏览器去请求新的地址。重定向需要用到HttpResponse对象调用sendRedirect()方法。

重定向示例:

protected void doPost(HttpServletRequest req, HttpServletResponse resp) {        try        {               resp.sendRedirect("http://www.bing.com");        } catch (IOException e)        {               // TODO Auto-generated catch block               e.printStackTrace();        } }