Forwarding and Redirection
success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
登陆成功<br>
欢迎你：
<%
String name=request.getParameter( "username" );
%>
<%=name%>
</body>
</html>
Forwarded
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>show</title>
</head>
<body>
<%
//设置编码
request.setCharacterEncoding( "UTF-8" );
String name=request.getParameter( "username" );
String pwd=request.getParameter( "password" );
if(name.equals( "zs" )&&pwd.equals( "abc" )){
request.getRequestDispatcher( "success.jsp" ).forward( request,response );
//可以获取到数据，并且地址栏没有改变（任然保留转发时的地址）
}else{
out.print( "登陆失败" );
}
%>
</body>
</html>
Redirect
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>show</title>
</head>
<body>
<%
//设置编码
request.setCharacterEncoding( "UTF-8" );
String name=request.getParameter( "username" );
String pwd=request.getParameter( "password" );
if(name.equals( "zs" )&&pwd.equals( "abc" )){
response.sendRedirect( "success.jsp" ); //重定向会导致数据丢失
}else{
out.print( "登陆失败" );
}
%>
</body>
</html>
Session
Cookie (client, not built-in object):
cookie: Key = value
is not built-in objects is provided by a packet java.servlet.http.Cookie java the
conventional method
public Cookie (String key, String value ) constructor
String getName (); Get name
String the getValue (); Get value
void the setMaxAge (int expiry); set period (seconds)
cookies generated by the server, and then sent to the client saved. Equivalent to the local cache of the role of
such visit, the first visit when the client generates a Cookie, sent to the client, then the second visit, it is a very fast.
Server sends to the client process
client is ready Cookie: respond.addCookie (Cookie cookie);
page jump (forward, redirect);
client obtains cookie: request. the getCookie ();
Note: a. Increase server cookie: response objects; client obtains the object; request objects
b. Not directly past a certain object only once to get all of the cookies
advantages: improve access rate, but poor security.
Disadvantages: poor security (passwords, etc.)
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>show</title>
</head>
<body>
<%
Cookie cookie1=new Cookie( "name","b" );
Cookie cookie2=new Cookie( "password","34" );
response.addCookie( cookie1 );
response.addCookie( cookie2 );
//页面跳转到客户端
response.sendRedirect( "result.jsp" );
%>
</body>
</html>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<%
Cookie[] cookies=request.getCookies();
for(Cookie cookie:cookies){
out.print(cookie.getName()+"--"+cookie.getValue()+"<br>");
}
%>
</body>
</html>
Showing results
View console found by F12, in addition to its own set of objects Cookies, there is a name for the JSESSIONID of Cookie
Cookie use Autosave username.
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java"
import="java.util.Date" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<%!
String name;
%>
<%
Cookie[] cookies=request.getCookies();
for(Cookie cookie:cookies){
if(cookie.getName().equals( "name" )){
name=cookie.getValue();
}
}
%>
<form action="show.jsp" method="post">
用户名：<input type="text" name="username" value="<%=(name==null?"":name)%>"/><br/>
//这里有个等式表达式包括三目运算符的地方，需要注意
密码：<input type="password" name="password"/><br/>
<input type="submit" value=登录>
</form>
</body>
</html>
show.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>show</title>
</head>
<body>
<%
//将相关信息存放到cookies中
request.setCharacterEncoding( "utf-8" );
String name=request.getParameter( "username" );
String password=request.getParameter( "password" );
Cookie cookie_name=new Cookie( "name",name );
response.addCookie( cookie_name );
%>
</body>
</html>
The first time into the browser, the user name is blank, but the second time of entry, automatically displays the user name entered for the first time
session (session)
Visit the website: Start - close Shopping: Browse - Payment - to withdraw from the series is a session
session mechanism:
when a client first request to the server, the server generates a session object (the user to save the customer information);
and each session object, there will be a unique sessionId (used to distinguish it from other session)
server will produce a cookie, and the cookie name = JSESSIONID, value = value sessionId server, then the server response to the client at the same time, send the cookie to the client, so far, the client will have a cookie (the JSESSIONID); therefore, the client can cookie and one-server session (corresponding to the JSESSIONID sessionId)
after a request, the server based on the client the cookie to serve JSESSIONID end of the session matching sessionId If a match (and the session cookie of JSESSIONID sessionId) describes the user is not the first visit, without logging in.
Commonly used methods:
String geiId (); // get sessionId
boolean the IsNew (); // determine whether it is a new user (first visit)
void the invalidate (); // the session failure; (Log cancellation)
setAttribute () ;
the getAttribute ();
void the setMaxInactiveInterval (); // set the maximum effective inactive time (sec)
int getMaxInactiveInterval (); // get the maximum effective period of inactivity
case, using the session to obtain a user name
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java"
import="java.util.Date" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<form action="check.jsp" method="post">
用户名：<input type="text" name="username" /><br/>
密码：<input type="password" name="password"/><br/>
<input type="submit" value=登录>
</form>
</body>
</html>
check.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<%
request.setCharacterEncoding( "utf-8" );
String name=request.getParameter( "username" );
String password=request.getParameter( "password" );
if(name.equals( "zs" )&&password.equals( "abc" )){
//只有登录成功session中才会存在username和password
session.setAttribute( "username",name );
session.setAttribute( "password",password );
request.getRequestDispatcher( "sessionDemo.jsp" ).forward( request,response );
}else {
response.sendRedirect( "index.jsp" );
}
%>
</body>
</html>
sessionDeom.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
欢迎你：
<%
String name= (String) session.getAttribute( "username" );
//如果用户没有登陆，直接访问sessionDemo.jsp则必然获得name==null
if(name!=null){
out.print( name );
}else{
response.sendRedirect( "index.jsp" );
}
%>
</body>
</html>
