javaWeb学习之旅5-请求转发、包含、重定向

逃离我推掉我的手 2022-02-25 18:18 212阅读 0赞

# 同一个web应用中各个servlet组件之间如何通讯 #

*  通过HttpServletRequest（或则是ServletContext）的Dispatcher对象来转发和包含请求
 *  通过HttpServletResponse的sendRedirect(String location)来重定向

# 请求转发 #

**请求转发图解：**  
![请求转发][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FMZWFycnJpbmc_size_16_color_FFFFFF_t_70]  
**请求转发代码：**

package com.my.test.web;
    
    import org.springframework.util.StringUtils;
    
    import javax.servlet.RequestDispatcher;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.io.PrintWriter;
    
    /**
     * @author lf
     * @Title: CheckServlet
     * @Description: TODO
     * @date 2019/4/2 11:42
     */
    public class ServletA extends HttpServlet {
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            PrintWriter out = resp.getWriter();
            String name = req.getParameter("name");
            if(StringUtils.isEmpty(name)){
                out.write("please input your name");
                return;
            }
            out.write("this is CheckServlet before forward to showServlet");
            System.out.println("before forward");
    
            //和ServletB共享requset
            req.setAttribute("msg","username is "+name);
            //请求转发
            RequestDispatcher requestDispatcher = getServletContext().getRequestDispatcher("/showServlet");
            requestDispatcher.forward(req,resp);
            
            //请求转发后一样会执行，只是写入out中的东西没有了
            out.write("this is CheckServlet after forward to showServlet");
            System.out.println("before after");
    
        }
    }

# 请求包含 #

**请求包含图解：**  
![请求包含][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FMZWFycnJpbmc_size_16_color_FFFFFF_t_70 1]  
**请求包含代码：**

package com.my.test.web;
    
    import javax.servlet.RequestDispatcher;
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.io.PrintWriter;
    
    /**
     * @author lf
     * @Title: MainServlet
     * @Description: TODO
     * @date 2019/4/2 13:55
     */
    public class MainServlet extends HttpServlet {
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //包含 BodySevlet和header.html 和 footer.html
            resp.setContentType("text/html");
            ServletContext servletContext = getServletContext();
            //获取对应的dispatcher
            RequestDispatcher bodyRequestDispatcher = servletContext.getRequestDispatcher("/body");
            RequestDispatcher headRequestDispatcher = servletContext.getRequestDispatcher("/html/header.html");
            RequestDispatcher footRequestDispatcher = servletContext.getRequestDispatcher("/html/footer.html");
            req.setAttribute("name","jack");
            PrintWriter out = resp.getWriter();
            out.println("<html><head></head><body>");
            //请求包含
            headRequestDispatcher.include(req,resp);
            bodyRequestDispatcher.include(req,resp);
            footRequestDispatcher.include(req,resp);
            out.println("</body></html>");
    
        }
    }

# 请求重定向 #

**请求重定向图解：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FMZWFycnJpbmc_size_16_color_FFFFFF_t_70 2]  
**请求重定向代码：**

package com.my.test.web;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.io.PrintWriter;
    
    /**
     * @author lf
     * @Title: RedirectServlet
     * @Description: TODO
     * @date 2019/4/2 14:05
     */
    public class RedirectServlet extends HttpServlet {
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            PrintWriter out = resp.getWriter();
            out.println("before redirect ");
            System.out.println("before redirect");
            String name = "rose";
            resp.sendRedirect("/real?msg="+name);
            System.out.println("after redirect");
            out.println("after redirect ");
    
        }
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FMZWFycnJpbmc_size_16_color_FFFFFF_t_70]: /images/20220225/c0d55ed110844549bd6e511dcabf6de4.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FMZWFycnJpbmc_size_16_color_FFFFFF_t_70 1]: /images/20220225/ae90a37176e846069ad4f71c974f47cd.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FMZWFycnJpbmc_size_16_color_FFFFFF_t_70 2]: /images/20220225/0d0e6e2a065443688397f8c05eeb885f.png