1 在HttpServlet中有操作属性的方法，在pageContext,request,session,application四个域对象中也有操作属性的方法。
<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> 页面2 </head> <body> request: <% request.setAttribute("requestValue",123); %> session: <% session.setAttribute("sessionValue",123); %> application: <% application.setAttribute("applicationValue",123); %> <a href="TestServlet">to servlet</a> <br/> <a href="ForwardServlet">to servlet2</a> <br/> <a href="RedirectServlet">to servlet3</a> <br/> </body> </html>
package servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class TestServlet extends HttpServlet { /** * Constructor of the object. */ public TestServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); Object requestVal = request.getAttribute("requestValue"); out.println("requestVal:"+requestVal); out.println("<br><br>"); Object sessionVal = request.getSession().getAttribute("sessionValue"); out.println("sessionVal:"+sessionVal); out.println("<br><br>"); Object applicationVal = getServletContext().getAttribute("applicationValue"); out.println("applicationVal:"+applicationVal); out.println("<br><br>"); } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here } }
2 请求的转发和重定向本质区别：前者只发了一次请求，而重定向发出了两次请求
请求的转发：地址栏是初次发出请求的地址；在最终的Servlet中，request对象和中转的request是同一个对象；只能转发给当前WEB应用的资源
请求的重定向：地址栏不再是初次发出的请求地址，地址栏为最后响应的那个地址,request对象和中转的request不是同一个对象。可以重定向到任何资源
public class ForwardServlet extends HttpServlet { /** * Constructor of the object. */ public ForwardServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String path = "TestServlet"; RequestDispatcher rd = request.getRequestDispatcher(path); rd.forward(request, response); }
public class RedirectServlet extends HttpServlet { /** * Constructor of the object. */ public RedirectServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String path = "TestServlet"; response.sendRedirect(path); }