转发和重定向的对比

转发和重定向的区别：

1、  转发不会改变浏览器的地址栏，而重定向会

2、  转发是在服务器端执行跳转，重定向是在浏览器端执行跳转

3、  转发客户端只发一次请求，重定向整个过程会发两次请求

4、  转发可以传递数据，而重定向不可以

5、  转发只是进行域内跳转，重定向可以跳转到其他应用（如：www.baidu.com）

转发：

servletDemo1:

@WebServlet("/demo1")public class ServletDemo1 extends HttpServlet {private static final long serialVersionUID = 1L;public ServletDemo1() {    }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {/*转发*/System.out.println("A:我要办事");System.out.println("B:你的事我办不了，我可以找人给你办");ServletContext application = this.getServletContext();application.getRequestDispatcher("/demo2").forward(request, response);System.out.println("事办完了");}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

servletDemo2:

@WebServlet("/demo2")public class ServletDemo2 extends HttpServlet {private static final long serialVersionUID = 1L;           public ServletDemo2() {    }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("C:***我能帮你办***");}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

当在浏览器中访问demo1时，demo1将请求（由服务器端的servletContext域对象）转发给demo2，并且在转发前后浏览器地址栏不会发生变化。

由输出结果看出，在执行跳转后，程序还是回到demo1执行剩余的代码。

转发数据的共享：

       更该上面程序的代码：

@WebServlet("/demo1")public class ServletDemo1 extends HttpServlet {private static final long serialVersionUID = 1L;public ServletDemo1() {    }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {/*转发*/ServletContext application = this.getServletContext();//两个servlet共享域数据application.setAttribute("name", "tom");application.getRequestDispatcher("/demo2").forward(request, response);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

@WebServlet("/demo2")public class ServletDemo2 extends HttpServlet {private static final long serialVersionUID = 1L;           public ServletDemo2() {    }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {ServletContext application = this.getServletContext();//两个servlet共享域数据String name = (String)application.getAttribute("name");System.out.println(name);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

因为这是一次访问过程，servletContext是域对象，所以进行跳转后，在demo2中可以得到demo1中的数据,因此转发可以共享数据。

 

重定向：

这是servletDemo7

@WebServlet("/demo7")public class ServletDemo7 extends HttpServlet {private static final long serialVersionUID = 1L;    public ServletDemo7() {        super();    }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//请求重定向System.out.println("A:我要借钱");System.out.println("B:我没钱，但我可以告诉你谁有");response.sendRedirect("/day09_response/demo8"); System.out.println("事办完了");}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

这是servletDemo8

WebServlet("/demo8")public class ServletDemo8 extends HttpServlet {private static final long serialVersionUID = 1L;           public ServletDemo8() {        super();    }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("C:我借给你...");}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

当在浏览器端访问servletDemo7时，浏览器的地址

访问结束后，浏览器的地址

由此可以看出，进行重定向改变了浏览器的地址栏信息。

 

执行结果:

由执行结果看出,在servletDemo7进行重定向之前，会把其中的所有代码执行完之后，在进行重定向操作。重定向时将新的url地址发给浏览器，再由浏览器进行重新访问，因此会改变浏览器地址栏的信息。所以重定向会发送两次访问请求。

若上面代码为：response.sendRedirect(“http://www.baidu.com”);会跳转到百度

用一张图来表示上述的过程：

好了，就写这么多，排版不太好看，各位大佬凑合看看！