Cookie&Session
首页（显示用户上次访问的时间）
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.write("您上次访问时间是：");
//1.获取用户上次访问的时间，显示
Cookie cookies[] = request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++){
Cookie cookie = cookies[i];
if(cookie.getName().equals("lastAccessTime")){
long time = Long.parseLong(cookie.getValue());
Date date = new Date(time);
out.write(DateFormat.getDateInstance(DateFormat.FULL).format(date));
}
}
//2.把本次的时间以cookie的形式回写给客户机 (lastAccessTime)
Cookie cookie = new Cookie("lastAccessTime",System.currentTimeMillis()+"");
response.addCookie(cookie);
- 一个Cookie只能标识一种信息，它至少含有一个标识该信息的名称（NAME）和设置值（VALUE）。
- 一个WEB站点可以给一个WEB浏览器发送多个Cookie，一个WEB浏览器也可以存储多个WEB站点提供的Cookie。
- 浏览器一般只允许存放300个Cookie，每个站点最多存放20个Cookie，每个Cookie的大小限制为4KB。
- 如果创建了一个cookie，并将他发送到浏览器，默认情况下它是一个会话级别的cookie（即存储在浏览器的内存中），用户退出浏览器之后即被删除。若希望浏览器将该cookie存储在磁盘上，则需要使用maxAge，并给出一个以秒为单位的时间。将最大时效设为0则是命令浏览器删除该cookie。
- 注意，删除cookie时，path必须一致，否则不会删除
显示用户上次浏览过的商品
public class CookieDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
//1.显示网站所有商品
out.print("本网站有如下书籍：<br/>");
Map<String,Book> map = DB.getMap();
for(Map.Entry<String, Book> entry : map.entrySet()){
Book book = entry.getValue();
out.print("<a href='/com/servlet/CookieDemo2?id="+book.getId()+"' target='_blank'>"+book.getName()+"</a><br/>");
}
out.print("您曾经看过如下商品：<br/>");
//2.显示用户曾经浏览过的商品 // bookHistory
Cookie cookie = null;
Cookie cookies[] = request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++){
if(cookies[i].getName().equals("bookHistory")){
cookie = cookies[i];
}
}
if(cookie!=null){
//找到了bookHistory这个cookie
String bookHistory = cookie.getValue(); //4_6_1
String ids[] = bookHistory.split("\\_");
for(String id: ids){
Book book = (Book) DB.getMap().get(id);
out.print(book.getName() + "<br/>");
}
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
class DB{
private static Map<String,Book> map = new HashMap<String, Book>();
static{
map.put("1", new Book("1","图书1","张三"));
map.put("2", new Book("2","图书2","李四"));
map.put("3", new Book("3","图书3","王五"));
map.put("4", new Book("4","图书4","赵六"));
map.put("5", new Book("5","图书5","韩七"));
}
public static Map<String, Book> getMap(){
return map;
}
}
class Book{
private String id;
private String name;
private String author;
public Book() {
super();
// TODO Auto-generated constructor stub
}
public Book(String id, String name, String author) {
super();
this.id = id;
this.name = name;
this.author = author;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
}
public class CookieDemo3 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
//1.根据用户带过来的id值，显示相应商品的信息
out.print("您想看的书的详细信息为：<br/>");
String id = request.getParameter("id");
Book book = (Book) DB.getMap().get(id);
out.print(book.getId() + "<br/>");
out.print(book.getName() + "<br/>");
out.print(book.getAuthor() + "<br/>");
//2.以cookie的形式回写该商品的id号给浏览器
String bookHistory = makeCookie(book.getId(),request);
Cookie cookie = new Cookie("bookHistory",bookHistory);
cookie.setMaxAge(10000);
response.addCookie(cookie);
}
//根据用户原来看过的书，以及现在看的书的id，构建新的cookie值
private String makeCookie(String id, HttpServletRequest request) {
//bookHistory=null 3 bookHistory=3
//bookHistory=2_1_5 3 bookHistory=3_2_1
//bookHistory=2 3 bookHistory=3_2
//bookHistory=2_3 3 bookHistory=3_2
//1.得到用户曾经看过的书
String bookHistory = null;
Cookie cookies[] = request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++){
if(cookies[i].getName().equals("bookHistory")){
bookHistory = cookies[i].getValue();
}
}
if(bookHistory==null){
bookHistory = id;
return bookHistory;
}
//bookHistory=1_2_5 代表用户曾经看一些书，接着程序要得到用户曾经看过什么书
String ids[] = bookHistory.split("_");
//为了检测数组中是否包含当前id，我们应该把数据转成集合，并且还要转成链表结构的集合
LinkedList<String> idList = new LinkedList(Arrays.asList(ids));
/*if(idList.contains(id)){
//bookHistory=2_3 3 bookHistory=3_2
idList.remove(id);
idList.addFirst(id);
}else{
//bookHistory=2_1_5 3 bookHistory=3_2_1
if(idList.size()>=3){
idList.removeLast();
idList.addFirst(id);
}else{
//bookHistory=2 3 bookHistory=3_2
idList.addFirst(id);
}
}*/
if(idList.contains(id)){
idList.remove(id);
}else{
if(idList.size()>=3){
idList.removeLast();
}
}
idList.addFirst(id);
StringBuffer sb = new StringBuffer();
for(String lid: idList){ //1_2_3_
sb.append(lid + "_");
}
return sb.deleteCharAt(sb.length()-1).toString();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
数据指纹(MD5:32|64)
public static String md5(String plainText) {
try {
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(plainText.getBytes());
byte b[] = md.digest();
int i;
StringBuffer buf = new StringBuffer("");
for (int offset = 0; offset < b.length; offset++) {
i = b[offset];
if (i < 0)
i += 256;
if (i < 16)
buf.append("0");
buf.append(Integer.toHexString(i));
}
System.out.println("result: " + buf.toString());// 32位的加密
return buf.toString();
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
class TokenProcessor{
//1. 把构造方法私有
//2. 自己产生一个类的对象
//3. 定义一个方法返回上面产生的对象
private TokenProcessor(){};
public static final TokenProcessor instance = new TokenProcessor();
public static TokenProcessor getInstance(){
return instance;
}
public String generateToken(){
//3843849384 9849238402840243802 983434
String token = System.currentTimeMillis() + "" + new Random().nextInt(99999999);
//数据指纹 数据摘要 md5
try {
MessageDigest md = MessageDigest.getInstance("md5");
byte md5[] = md.digest(token.getBytes()); //128位 16【12，23，34，544543543543，】
//base64编码 SABDSSDSD
BASE64Encoder encoder = new BASE64Encoder();
return encoder.encode(md5);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
}
防止表单重复提交
<form action="/com/servlet/FormSubmitServlet" method="post" onsubmit="return dosubmit()">
用户名：<input type="text" name="username"><br/>
<input id="submit" type="submit" value="提交">
</form>
function dosubmit(){
document.getElementById("submit").disabled = 'disabled';
return true;
}
response.setContentType("text/html;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
String token = TokenProcessor.getInstance().generateToken();
request.getSession().setAttribute("token", token);
out.print("<form action='/com/servlet/FormSubmitServlet' method='post'>");
out.print("<input type='hidden' name='token' value='"+token+"'>");
out.print("<input type='text' name='username'>");
out.print("<input type='submit' value='提交'>");
out.print("</form>");
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
boolean b = isToken(request);
if(!b){
//用户带过来的令牌无效，阻止提交
System.out.println("你是重复提交！！");
return;
}
//用户带过来的令牌有效，处理提交
request.getSession().removeAttribute("token");
String username = request.getParameter("username");
//把用户提交的数据保存到数据库中
System.out.println("处理提交请求，把" + username + "保存到数库中！！");
}
//判断用户带过来的令牌是否有效
private synchronized boolean isToken(HttpServletRequest request) {
String client_token = request.getParameter("token");
if(client_token==null){
return false;
}
String server_token = (String) request.getSession().getAttribute("token");
if(server_token==null){
return false;
}
if(!client_token.equals(server_token)){
return false;
}
return true;
}