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java web 学习 --第五天（Java三级考试）

2013-12-04 23:13 525 查看
第四天的学习内容：/article/4969930.html

Response对象

response对象主要是向客户端浏览器发送二进制数据，如输出Cookie、设置HTTP文件头信息等方面内容

response主要功能和方法

getWrite() 获得PrintWrite类的对象实例，实现向浏览器输出信息

addCookie() 在客户端计算机磁盘上创建出Cookie对象实例，在Cookie对象实例可以保存客户端信息特征，然后采用request对象的getCookies()方法获取客户机所有Cookie对象

addHeader() 添加HTTP头文件信息，将信息传送到客户浏览器中

containsHeader() 判断指定名字的文件头是否存在，返回布尔型true / false

setHeader() 设置指定名字HTTP头文件的值，若该值存在则覆盖

sendRedirect() 重定向到由参数targetURL所指示的目标JSP页面或Servlet程序，不能向客户端输出信息

setContentType() 在相应中可以设置内容的文档数据类型和格式

setBufferSize() 设置Web容器的缓冲区大小，配合getBufferSize()方法返回该缓冲器信息

利用response对象实现向客户机种写入Cookie信息

Cookie或称Cookies，是指Web应用系统为了辨别访问者身份而存储在客户机中的一个文本文件，其中包含特定数据，比如登陆邮箱：

可以把用户名和密码放在客户机Cookie中，下次访问不需要再输入用户名密码

读取Cookie文件信息，使用Cookie类中的getName()和getValue()返回客户端的某一个特定Cookie对象名所对应的值。而利用response对象addCookie(cookie data )方法可以写入Cookie对象中所包装的数据。

实例：在系统首页中添加读写Cookie信息

在index jsp页面中添加如下代码

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@page import="java.util.Date" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP add Cookie information </title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>

<body>
<%! String lastAccessTime=null;      //the last time view this web site
String nowAccessTime=null;
Cookie mycookie=null;
Cookie[] cookies=null;
Date now=null;
%>
<%
cookies=request.getCookies();               // use request class getCookie method to get cookies if there is no cookie info then add new
now=new Date();
if(cookies==null)
{
lastAccessTime=(now.getYear()+1900+"Year"+now.getMonth()+"Month"+now.getDay()+"Day"+now.getHours()+"Hour"+now.getMinutes()+"Minute"+now.getSeconds()+"Second");
mycookie=new Cookie("lastAccessTime",lastAccessTime);
mycookie.setMaxAge(30*24*60*60); // 30 days 24hours 60mins 60 seconds
response.addCookie(mycookie);
}
else
for(int index=0;index<cookies.length;index++)
{
if(cookies[index].getName().equals("lastAccessTime"))
{
lastAccessTime=cookies[index].getValue();
nowAccessTime=(now.getYear()+1900+"Year "+now.getMonth()+" Month "+now.getDay()+" Day "+now.getHours()+" Hour "+now.getMinutes()+" Minute "+now.getSeconds()+" Second");
mycookie=new Cookie("lastAccessTime",nowAccessTime);
mycookie.setMaxAge(30*24*60*60); // 30 days 24hours 60mins 60 seconds
response.addCookie(mycookie);
break;
}
}
out.print("the last time your visit this system is "+lastAccessTime);

%>
</body>
</html>


首先用request的getCookie获取一下cookie，如果没有cookie信息，使用response的addCookie增加cookie信息

区分重定向与跳转方式的区别

请求转发过程中客户端浏览器只向server端产生一次请求，而重定向是两次；

请求转发时在浏览器的URL地址栏中的信息不会发生改变，仍然是原来的URL而重定向将会转向目标URL

使用HTTP请求转发：

使用转发由于只有一次请求，所以在一个页面的request.setAttribute 能够在跳转后的页面使用request.getAttribute获取其属性值

使用4个jsp页面和一个类文件

新建 login.jsp 设置登陆框，用户名密码。。。。。

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ page isErrorPage="true" errorPage="error.jsp"  %>

<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>This is my first JSP page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>

<body>

<form method="post" action="response.jsp" >
username:
<input type="text" name="user" >
<br>
password:
<input type="password" name="password">
<br>
userType:
<select name="userType">
<option value="user" >user</option>
<option value="master"> master</option>
</select>

<input type="submit" name="submit" />
</form>

</body>
</html>


新建response.jsp页面当用户名是：young并且密码是1234跳转到index.jsp否则跳转到error.jsp，引入userInfo类，使用其verifyID方法校验用户名密码

userinfo类代码：

package mypackage;

public class userInfo {

/**
* @param args
* two parameters add get/set methods
*/

String userName=null;
String passWord=null;
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getPassWord() {
return passWord;
}
public void setPassWord(String passWord) {
this.passWord = passWord;
}

public boolean  verifyID( )
{
if(userName.equals("young") && passWord.equals("1234"))
{
System.out.print("login successful\n");
return true;
}
else
{
System.out.print("login failure\n");
return false;
}

}

}


代码如下：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<jsp:useBean id="user" class="mypackage.userInfo" scope="session" ></jsp:useBean>

<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP 'response.jsp' starting page</title>

<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->

</head>

<body>
<%!
String targetPage=null;
RequestDispatcher rd=null;
%>
<%
user.setUserName(request.getParameter("user"));
user.setPassWord(request.getParameter("password"));

if(user.verifyID())
{
request.setAttribute("userNameString",user.getUserName());
targetPage="index.jsp";
System.out.print(user.getUserName());
}
else
{
request.setAttribute("errorMSG","sorry,Login FAILED.\n");
targetPage="error.jsp";
}
rd=request.getRequestDispatcher(targetPage);
rd.forward(request,response);
%>
</body>
</html>


新建error.jsp 这个页面会获取response.jsp传递过来的errorMSG

<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP 'error.jsp' starting page</title>

<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->

</head>

<body>
errorMSG<br>
<%=request.getAttribute("errorMSG") %>
</body>
</html>


新建index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@page import="java.util.Date" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP add Cookie information </title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>

<body>
welcome <%=request.getAttribute("userNameString") %>
<%! String lastAccessTime=null;      //the last time view this web site
String nowAccessTime=null;
Cookie mycookie=null;
Cookie[] cookies=null;
Date now=null;
%>
<%
cookies=request.getCookies();               // use request class getCookie method to get cookies if there is no cookie info then add new
now=new Date();
if(cookies==null)
{
lastAccessTime=(now.getYear()+1900+"Year"+now.getMonth()+"Month"+now.getDay()+"Day"+now.getHours()+"Hour"+now.getMinutes()+"Minute"+now.getSeconds()+"Second");
mycookie=new Cookie("lastAccessTime",lastAccessTime);
mycookie.setMaxAge(30*24*60*60); // 30 days 24hours 60mins 60 seconds
response.addCookie(mycookie);
}
else
for(int index=0;index<cookies.length;index++)
{
if(cookies[index].getName().equals("lastAccessTime"))
{
lastAccessTime=cookies[index].getValue();
nowAccessTime=(now.getYear()+1900+"Year "+now.getMonth()+" Month "+now.getDay()+" Day "+now.getHours()+" Hour "+now.getMinutes()+" Minute "+now.getSeconds()+" Second");
mycookie=new Cookie("lastAccessTime",nowAccessTime);
mycookie.setMaxAge(30*24*60*60); // 30 days 24hours 60mins 60 seconds
response.addCookie(mycookie);
break;
}
}
out.print("the last time your visit this system is "+lastAccessTime);

%>
</body>
</html>


登陆成功会显示： 可以看出，跳转后的页面URL仍然是跳转前的URL并未发生任何变化，由于只进行一次请求，所以request.setAttribute 和request.getAttribute能够正常工作



登陆失败：



而是用response.sendRedirect()会出现2次请求不能再是用request的对象包装和传递参数，可以使用session.setAttribute("NAME","VALUE")使用EL表达式语句${sesstionScope.userNameString}

从session会话对象中获取传递的参数,同时重定向后的URL为重定向页面的URL。
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