定向转发的特点：
(1). 实行转发时浏览器上的网址不变 （如果你这点忽视了，那你就要接受我无尽的鄙视吧！ 哇咔咔~~~）
(2). 实行转发时 ： 只有一次请求。 不信，看这下面的图： （俗话说，没图说个jb）
(3). 定向转发的网址必须是本站点的网址. (因为它不消除，消除数据)
(4) 定向转发：以前的request中存放的变量不会失效，就像把两个页面拼到了一起。
实现的两个API：
1 RequestDispatcher rd
2 = request.getRequestDispatcher("Demo_1/Login.jsp");
3
4 rd.forward(request, response);
定向转发
关于定向转发实现selected选项功能：
上面这个控件的代码：
JSP代码：
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <%
3 String path = request.getContextPath();
4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
5 %>
6
7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
8 <html>
9 <head>
10 <base href="<%=basePath%>">
11 <title>注册页面</title>
12 <meta http-equiv="pragma" content="no-cache">
13 <meta http-equiv="cache-control" content="no-cache">
14 <meta http-equiv="expires" content="0">
15 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
16 <meta http-equiv="description" content="This is my page">
17 <!--
18 <link rel="stylesheet" type="text/css" href="styles.css">
19 -->
20 </head>
21
22 <body>
23 <% String authority = (String) request.getAttribute("authority"); %>
24 <form action="LoginServlet" method="post" >
25 username :<input type="text" name="username" value="<%=null==request.getAttribute("username")?"":request.getAttribute("username")%>"><br>
26 password :<input type="password" name="password"><br>
27
28 authority:
29 <select name="authority">
30 <option value="1"<%="1".equals(authority)?"selected":""%>>common user</option>
31
32 <option value="2"<%="2".equals(authority)?"selected=‘selected‘":""%>>administrator</option>
33
34 </select><br>
35
36 <input type="submit" value="submit">
37
38 </form>
39 </body>
40 </html>
效果图：
关于： 然后需要一个Servlet 类： （即纯java文件）
1 package Demo;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5
6 import javax.servlet.RequestDispatcher;
7 import javax.servlet.ServletException;
8 import javax.servlet.http.HttpServlet;
9 import javax.servlet.http.HttpServletRequest;
10 import javax.servlet.http.HttpServletResponse;
11 import javax.servlet.http.HttpSession;
12
13 public class LoginServlet extends HttpServlet {
14
15 public void doGet(HttpServletRequest request, HttpServletResponse response)
16 throws ServletException, IOException {
17 String username = request.getParameter("username");
18 String password =request.getParameter("password");
19 String authority =request.getParameter("authority");
20
21 Login log = new Login();
22 HttpSession session = request.getSession();
23 if("1".equals(authority))
24 {
25 // 登录的是普通用户
26 if("zhangsan".equals(username) && "123".equals(password))
27 {
28 // 将用户的信息放置到Session当中
29
30 log.setUsername(username);
31 log.setAuthority(authority);
32 log.setPassword(password);
33 session.setAttribute("log", log);
34 }else {
35
36 //定向转发
37 request.setAttribute("username",username);
38 request.setAttribute("password", password);
39 request.setAttribute("authority",authority);
40 RequestDispatcher rd = request.getRequestDispatcher("Demo_1/Login.jsp");
41 rd.forward(request, response);
42 }
43 }
44 else if("2".equals(authority)){
45 // 登录的是系统管理员
46 if("Tom".equals(username) && "456".equals(password))
47 {
48 log.setAuthority(authority);
49 log.setPassword(password);
50 log.setUsername(username);
51 session.setAttribute("log",log);
52 }
53 else {
54
55 // 采取的是定向转发
56
57 request.setAttribute("username",username);
58 request.setAttribute("password", password);
59 request.setAttribute("authority",authority);
60 RequestDispatcher rd = request.getRequestDispatcher("Demo_1/Login.jsp");
61 rd.forward(request, response);
62 }
63 } else {
64
65 request.setAttribute("username",username);
66 request.setAttribute("password", password);
67 request.setAttribute("authority",authority);
68 RequestDispatcher rd = request.getRequestDispatcher("Demo_1/Login.jsp");
69 rd.forward(request, response);
70
71 }
72
73 }
74
75 public void doPost(HttpServletRequest request, HttpServletResponse response)
76 throws ServletException, IOException {
77 this.doGet(request, response);
78 }
79 }
一个 javabean文件：
1 package Demo;
2
3 //设置一个JavaBean 类
4
5 public class Login {
6
7 private String username ;
8 private String password ;
9 private String authority ;
10
11 public String getUsername() {
12 return username;
13 }
14
15 public void setUsername(String username) {
16 this.username = username;
17 }
18
19 public String getPassword() {
20 return password;
21 }
22
23 public void setPassword(String password) {
24 this.password = password;
25 }
26
27 public String getAuthority() {
28 return authority;
29 }
30
31 public void setAuthority(String authority) {
32 this.authority = authority;
33 }
34 }
重定向的特点：
（１）执行重定向时浏览器上的网址改变．
（２）重定向实际上产生了两次请求 （看下面的图）
(3)执行重定向时 的网址可以是任何网址。
调用的 API 函数：
1 response.sendRedirect("Demo_1/Login.jsp? username="+username+"&authority="+authority);
对于定向转发和重定向的实际执行情况，可以简单的慨括为：
对于重定向：
发送请求 -->服务器运行-->响应请求，返回给浏览器一个新的地址与响应码-->浏览器根据响应码，判定该响应为重定向，自动发送一个新的请求给服务器，请求地址为之前返回的地址-->服务器运行-->响应请求给浏览器
对于定向的转发：
发送请求 -->服务器运行-->进行请求的重新设置，例如通过request.setAttribute(name,value)-->根据转发的地址，获取该地址的网页-->响应请求给浏览器
特别需要注意的是：
重定向：以前的request中存放的变量全部失效，并进入一个新的request作用域。
转发：以前的request中存放的变量不会失效，就像把两个页面拼到了一起。
然后运用重定向实现<select> 下拉列表的代码：
对于JSP：
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <%
3 String path = request.getContextPath();
4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
5 %>
6
7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
8 <html>
9 <head>
10 <base href="<%=basePath%>">
11 <title>注册页面</title>
12 <meta http-equiv="pragma" content="no-cache">
13 <meta http-equiv="cache-control" content="no-cache">
14 <meta http-equiv="expires" content="0">
15 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
16 <meta http-equiv="description" content="This is my page">
17 <!--
18 <link rel="stylesheet" type="text/css" href="styles.css">
19 -->
20 </head>
21
22 <body>
23 <%
24 String username = request.getParameter("username");
25 String authority = request.getParameter("authority");
26 %>
27 <form action="LoginServlet" method="post" >
28 username :<input type="text" name="username" <%= null == username ? "":username %> ><br>
29 password :<input type="password" name="password"><br>
30
31 authority:
32 <select name="authority">
33 <option value="1" <%= "1" == authority ?"":"selected"%> >common user</option>
34
35 <option value="2" <%= "2" == authority ?"":"selected"%> >administrator</option>
36
37 </select><br>
38
39 <input type="submit" value="submit">
40
41 </form>
42 </body>
43 </html>
对于Servlet类：
1 package Demo;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5
6 import javax.servlet.RequestDispatcher;
7 import javax.servlet.ServletException;
8 import javax.servlet.http.HttpServlet;
9 import javax.servlet.http.HttpServletRequest;
10 import javax.servlet.http.HttpServletResponse;
11 import javax.servlet.http.HttpSession;
12
13 public class LoginServlet extends HttpServlet {
14
15 public void doGet(HttpServletRequest request, HttpServletResponse response)
16 throws ServletException, IOException {
17 String username = request.getParameter("username");
18 String password =request.getParameter("password");
19 String authority =request.getParameter("authority");
20
21 Login log = new Login();
22 HttpSession session = request.getSession();
23 if("1".equals(authority))
24 {
25 // 登录的是普通用户
26 if("zhangsan".equals(username) && "123".equals(password))
27 {
28 // 将用户的信息放置到Session当中
29
30 log.setUsername(username);
31 log.setAuthority(authority);
32 log.setPassword(password);
33 session.setAttribute("log", log);
34 }else {
35 //执行重定向函数
36 response.sendRedirect("Demo_1/Login.jsp? username="+username+"&authority="+authority);
37 }
38 }
39 else if("2".equals(authority)){
40 // 登录的是系统管理员
41 if("Tom".equals(username) && "456".equals(password))
42 {
43 log.setAuthority(authority);
44 log.setPassword(password);
45 log.setUsername(username);
46 session.setAttribute("log",log);
47 }
48 else {
49 // 采取的是重定向
50 response.sendRedirect("Demo_1/Login.jsp?username="+username+"&authority="+authority);
51 }
52 } else {
53
54 // 采取的是重定向
55 response.sendRedirect("Demo_1/Login.jsp?username="+username+"&authority="+authority);
56 }
57
58 }
59
60 public void doPost(HttpServletRequest request, HttpServletResponse response)
61 throws ServletException, IOException {
62 this.doGet(request, response);
63 }
64 }
对于JavaBean类：
1 package Demo;
2
3 //设置一个JavaBean 类
4
5 public class Login {
6
7 private String username ;
8 private String password ;
9 private String authority ;
10
11 public String getUsername() {
12 return username;
13 }
14
15 public void setUsername(String username) {
16 this.username = username;
17 }
18
19 public String getPassword() {
20 return password;
21 }
22
23 public void setPassword(String password) {
24 this.password = password;
25 }
26
27 public String getAuthority() {
28 return authority;
29 }
30
31 public void setAuthority(String authority) {
32 this.authority = authority;
33 }
34 }
显示的效果：
时间： 2024-10-09 16:42:36