JAVA - 【Tomcat】Servlet Cookie與Session

目錄

• Cookie
  • cookie是什麼?
  • javax.servlet.http.Cookie
  • 獲取與添加
  • 示例：上次訪問時間
  • 示例：歷史記錄
• Session
  • Session原理
  • JSP默認內置session對象
  • 獲得Session
  • API
  • 示例：登錄驗證碼

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<一> Cookie

1> cookie是什麼？

客戶端技術，服務器將每個用戶的數據以cookie的形式寫給各自的瀏覽器；

• 會話級別cookie（MaxAge=-1）
• 本地cookie（MaxAge>0）
• 刪除cookie（MaxAge=0）

2> javax.servlet.http.Cookie

名稱必須遵守 RFC 2109。

這意味着它只能包含 ASCII 字母數字字符，不能包含逗號、分號或空格，也不能以 $ 字符開頭；cookie 的名稱在創建之後不得更改。

Cookie：
    javax.servlet.http.Cookie
        cookie值可以唯一標識客戶端
            每個web服務器20個cookie
            總共300個cookie
            每個cookie大小限定4K
        new Cookie(String,String)
                getName()
                getValue(String)
                ck.setPath("/");
                    *注意cookie保存的時間是訪問當前Servlet的時間，與這裏設置的Path無關，這裏的Path只其攜帶作用
                ck.setMaxAge(60*60*24);

3> 獲取與添加

從請求中獲取cookies + 將cookie返回給客戶端

void addCookie(Cookie cookie) 
    HttpServletResponse
        *響應消息頭
            Set-Cookie頭字段

Cookie[] getCookies()
    HttpServletRequest

4> 示例：上次訪問時間

JDK1.8新時間類：https://blog.csdn.net/qq_42292831/article/details/105342748

package xyz.kuoa.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 測試cookie
 * @author X
 *
 */
public class ServletDemo1 extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		response.setContentType("text/html;charset=UTF-8");
		
		//獲取cookie
		Cookie[] cks = request.getCookies();
		String time = "";
		PrintWriter out = response.getWriter();
		for (int i = 0; cks!=null&&i < cks.length; i++) {
			if("lastAccessTime".equals(cks[i].getName())){
				time = cks[i].getValue();
				LocalDateTime tempTime = LocalDateTime.parse(time,DateTimeFormatter.ofPattern("yyyyMMddHHmmss"));
				time = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss").format(tempTime);
				out.print("你上次訪問的時間爲："+time);
			}
		}
		
		//寫入cookie
		//cookie參數只能爲ASCII字母數字，不能有其他字符
		String time1 = DateTimeFormatter.ofPattern("yyyyMMddHHmmss").format(LocalDateTime.now());
		Cookie ck = new Cookie("lastAccessTime",time1);
		//訪問哪些路徑時攜帶當前cookie(以該路徑爲前綴)
		//注意cookie保存的時間是訪問當前Servlet的時間，與這裏設置的Path無關，這裏的Path只其攜帶作用
		//ck.setPath("/");
		ck.setMaxAge(60*60*24);
		response.addCookie(ck);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


	}

}

5> 示例：歷史記錄

• Book.java

package xyz.kuoa.entity;

public class Book {
	private String id;
	private String name;
	private double price;
	private String author;

	public Book(String id, String name, double price, String author) {
		super();
		this.id = id;
		this.name = name;
		this.price = price;
		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 double getPrice() {
		return price;
	}

	public void setPrice(double price) {
		this.price = price;
	}

	public String getAuthor() {
		return author;
	}

	public void setAuthor(String author) {
		this.author = author;
	}

	@Override
	public String toString() {
		return "Book [id=" + id + ", name=" + name + ", price=" + price + ", author=" + author + "]";
	}
}

• DBUtils.java

package xyz.kuoa.util;

import java.util.HashMap;
import java.util.Map;

import xyz.kuoa.entity.Book;

public class DBUtils {
	private static Map<String,Book> books = new HashMap<>();
	
	static{
		books.put("1", new Book("1","《時間簡史》",89.9,"霍金"));
		books.put("2", new Book("2","《C語言入門》",75.9,"小A"));
		books.put("3", new Book("3","《Java入門》",52.9,"小B"));
		books.put("4", new Book("4","《C#入門》",53.9,"小C"));
		books.put("5", new Book("5","《PHP入門》",64.9,"小D"));
	}

	public static Map<String, Book> findAllBooks() {
		return books;
	}
	
	public static Book findBookById(String id){
		return books.get(id);
	}
	
}

• ServletDemo1.java

package xyz.kuoa.history;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import xyz.kuoa.entity.Book;
import xyz.kuoa.util.DBUtils;

public class ServletDemo1 extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();

		out.print("本網站書籍列表：<br/>");
		Map<String, Book> books = DBUtils.findAllBooks();
		for (Map.Entry<String, Book> b : books.entrySet()) {
			out.print("<a href='" + request.getContextPath() + "/servlet/showBookDetail?id=" + b.getKey()
					+ "' target='_blank'>" + b.getValue().getName() + "<a><br/>");
		}

		out.print("<hr/>您瀏覽過的書籍列表：<br/>");
		Cookie[] cookies = request.getCookies();
		String idString = "";
		for (int i = 0; cookies!=null&&i < cookies.length; i++) {
			if("historyBookId".equals(cookies[i].getName())){
				idString = cookies[i].getValue();
				String[] ids = idString.split("-");
				for (String id : ids) {
					String name = DBUtils.findBookById(id).getName();
					out.print(name+"<br/>");
				}
				break;
			}
		}
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

	}

}

• ShowBookDetail.java

package xyz.kuoa.history;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import xyz.kuoa.entity.Book;
import xyz.kuoa.util.DBUtils;

public class ShowBookDetail extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();

		// 顯示圖書的詳細信息
		// 獲得get方式提交的ID
		String id = request.getParameter("id");
		Book book = DBUtils.findBookById(id);
		out.print(book + "<br/>");

		// 把當前瀏覽過得書籍ID寫回到客戶端
		String historyBookId = organizeId(id, request);
		Cookie ck = new Cookie("historyBookId", historyBookId);
		ck.setPath("/");
		//ck.setMaxAge(60 * 60 * 24);
		response.addCookie(ck);
	}

	private String organizeId(String id, HttpServletRequest request) {
		String idString = "";
		Cookie[] cookies = request.getCookies();
		for (int i = 0; cookies != null && i < cookies.length; i++) {
			if ("historyBookId".equals(cookies[i].getName())) {
				idString = cookies[i].getValue();
				break;
			}
		}
		if (idString == "") {
			idString = id;
		} else {
			idString = id+"-"+idString;
			// 去重
			String[] ids = idString.split("-");
			List<String> list = new LinkedList<>();
			Collections.addAll(list, ids);
			for (int i = 0; i < list.size(); i++) {
				for (int j = i + 1; j < list.size(); j++) {
					if (list.get(i).equals(list.get(j))) {
						list.remove(j);
						j--;
					}
				}
			}
			idString = "";
			for (int i = 0; i < list.size(); i++) {
				if(i==0){
					idString = list.get(i);
				}else{
					idString = idString+"-"+list.get(i);
				}
			}
		}
		return idString;
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

	}

}

<二> Session

☞ 瀏覽器關閉後一個會話(Session)結束：每個瀏覽器維護一個會話；

☞ 爲什麼要使用Session：

• session是服務端技術，維護自身域對象，同一會話下，一個應用可共享數據；
• 域對象值可以爲Object，cookie只能爲String（ASCII字母數字字符）

1> Session原理

Session底層依賴cookie

2> JSP默認內置session對象

3> 獲得Session

HttpSession session = request.getSession();
	session.setAttribute("A","AAA");
	String a = (String)session.getAttribute("A");

3> API

• void setAttribute(String, Object)
• Object getAttribute(String)
• void removeAttribute(String)
• 獲得保存在cookie中的id
  • session.getId();
• 設置過期時間
  • session.setMaxInactiveInterval(60);
• 立馬銷燬session
  • session.invalidate();

☞ 另一種設置session過期時間的方式（web.xml）：

<!-- 單位：分鐘 -->

<session-config>
	<session-timeout>10</session-timeout>
</session-config>

4> 示例：登錄驗證碼

https://kylee.blog.csdn.net/article/details/106403717