RequestDispathcher

使用HttpServletRequest的getRequestDispatcher(“Servlet-URL”) 获得对象

RequestDispatcher dispatch = req.getRequestDispatcher(“/Test1”);

include()

将另一个servlet包括进进目前的操作流程中。

以下代码会输出

Dispatch

Test1

Done

/Dispatch    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        PrintWriter output = resp.getWriter();        output.println("Dispatch
");        RequestDispatcher dispatch = req.getRequestDispatcher("/Test1");        dispatch.include(req, resp);;        output.println("Done
");    }

/Test1    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {            PrintWriter output = resp.getWriter();            output.println("Test1
");    }

forward()

将请求转发给另一个servlet，只是服务器端的转发，对于客户端并无任何影响

PS:调用forWard()之前不能有任何相应确认，如果设置了相应但还未确认(例如println()后还没有flush())，则所有相应会被忽略.如果已经有相应确认，会报出java.lang.IllegalStateException异常

以下代码会转向Test1，而忽略之forward之前的println输出

PrintWriter output = resp.getWriter();        output.println("Dispatch
");        RequestDispatcher dispatch = req.getRequestDispatcher("/Test1");        dispatch.forward(req, resp);;        output.println("Done
");

以下代码会直接报错，因为已经有相应确认

PrintWriter output = resp.getWriter();        output.println("Dispatch
");        output.flush();         RequestDispatcher dispatch = req.getRequestDispatcher("/Test1");        dispatch.forward(req, resp);;        output.println("Done
");

请求范围属性

当调派请求的过程中有需要共享的属性，可以使用HttpServletRequest的方法

**setAttribute() 指定名称与对象** **getAttribute() 指定名称获取对象** **getAttributeNames() 获取所有属性名称** **removeAttribute() 移除属性**

以下代码的Test1通过getAttribute(“name”)获取到name的集合，需要通过强制转换后才能使用。

/Dispatch    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        PrintWriter output = resp.getWriter();        List
     
       list = new  ArrayList<>();        list.add("Tom");        list.add("jerry");        req.setAttribute("name", list);     // 传入字符串和对象        RequestDispatcher dispatch = req.getRequestDispatcher("/Test1");        dispatch.forward(req, resp);        output.println("Done
      
");    }

/Test1    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {            PrintWriter output = resp.getWriter();            output.println("Test1
");            List name = (List)req.getAttribute("name");            output.println(name.get(1)+"
");    }

sendRedirect()

要求浏览器重新请求一个URL，客户端的地址栏会改变

protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        String url = req.getParameter("url");        resp.sendRedirect(url);    }

在跳转之前不可以有相应被确认,否则会产生java.lang.IllegalStateException 异常

protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        PrintWriter output = resp.getWriter();        output.println("2333");        output.flush();        String url = req.getParameter("url");        resp.sendRedirect(url);    }

跳转时可以附带参数,方式类比于GET方式的URL

String name = req.getParameter("name");        PrintWriter output = resp.getWriter();        resp.sendRedirect("http://localhost:8080/Test/Redirect_Para?name="+name);

PS:

只能用转向方式来访问WEB-INF目录下的JSP,不用采用重定向的方式请求该目录里面的任何资源同一个请求周期中，HttpServletResponse的getWriter()与getOutputStream()只能择一使用，否则会丢出IllegalStateException