Using cookie technology to realize historical browsing records and control the number of displays

Use cookie Technology enables historical browsing records , And only show 3 History browsing records , The records of each visit are put at the top main. Need to know cookie Knowledge points of : cookie Save on client ; The server is created cookie (Cookie cookie = new Cookie(String cookieName,String cookieValue), Use response.add(Cookie） Return to the client ; The next time you visit, the browser will carry this cookie Send it to the server together with the request parameters . Server receive cookie Use request.getCookies(); The return is Cookie [] . You need to judge this when using it cookie Is it null.

cookie The validity of the :cookie.setMaxAge(0) ,response.addCookie(cookie); Tell the browser cookie invalid . Start coding : First step : Prepare the data :

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

import com.itmayiedu.bean.Book; /**

• Simulate the data in the database
• @author Administrator

*/ public class DBUtils { private static Map<Integer, Book> books = new HashMap();

static{
	books.put(1, new Book(1,"java Introduction learning ","tom"));
	books.put(2, new Book(2, "c#", "jack"));
	books.put(3, new Book(3, "python", "marray"));
	books.put(4, new Book(4," big data ","kevin"));
	books.put(5, new Book(5, "javascipt introduction ", "lilie"));
	
}

public static Map<Integer, Book> getBookAll(){
	return DBUtils.books;
}

// according to id  Get book information  key  Just count id.
public static Book getBookById(Integer id){
	return books.get(id);
}

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}

The second step : import java.io.IOException; import java.io.PrintWriter; import java.util.Map; import java.util.Map.Entry; import java.util.Set;

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

import com.itmayiedu.bean.Book; import com.itmayiedu.util.DBUtils;

/**

• Display the data we need to access in the browser
• @author Administrator

*/

@WebServlet(“/showBookAll”) public class ShowBookAll extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 response.setContentType("text/html;charset=utf-8");
 // Show all books 
 PrintWriter writer = response.getWriter();
 writer.println(" The book list :");
 
 Map<Integer, Book> bookMap = DBUtils.getBookAll();
 Set<Entry<Integer,Book>> entrySet = bookMap.entrySet();
 for (Entry<Integer, Book> entry : entrySet) {
	Book book = entry.getValue();
	 
	 writer.print("<br/><a href='http://localhost:8080"+request.getContextPath()+"/bookView?id="+book.getId()+"'>"+book.getName()+"</a>");
	 
}
 
 writer.println("<br/> History of the visit <br/>");
 // obtain cookie
 Cookie[] cs = request.getCookies();
 if(cs !=null){
	 for (Cookie c : cs) {
		if("historyIDs".equals(c.getName())){
			String historyIDs = c.getValue();
			String[] split = historyIDs.split("-");
			for (String id : split) {
				Book book = DBUtils.getBookById(Integer.parseInt(id));
				writer.println("<br><a href='http://localhost:8080"+request.getContextPath()+"/bookView?id="+book.getId()+"'>"+book.getName()+"</a>");
			
			}
		}
	}
 }
 
 
}

 
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	 doGet(request, response);
}

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}

The third step : import java.io.IOException; import java.util.Arrays; import java.util.LinkedList; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;

import com.itmayiedu.bean.Book; import com.itmayiedu.util.DBUtils;

/**

• Detailed information processing
• @author Administrator

*/

@WebServlet(“/bookView”) public class BookViewServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(“text/html;charset=utf-8”); // obtain id String idStr = request.getParameter(“id”); System.out.println(“ Now visit id:” + idStr); Book book = DBUtils.getBookById(Integer.parseInt(idStr));

	response.getWriter().println(" Details :" + book.toString());

	LinkedList<String> list = new LinkedList<>();

	StringBuffer sb = new StringBuffer();

	// TODO  Record browsing information , hold id Save in cookie in , Show on page 
	//  Put the visited id Put in cookie in 
	Cookie[] cs = request.getCookies();
	if (cs != null) {
		//  It means that there are already cookie It's preserved id
		// historyIDs = 1-2-3-4

		// 1-2-3-4-1 1-2-3-4-4 1-2-3-4 3
		for (Cookie c : cs) {
			if ("historyIDs".equals(c.getName())) {
				String idValues = c.getValue();
				System.out.println(" Previously visited histroyIDs:" + idValues);

				//  Page display only 3 individual 
				String[] ids = idValues.split("-");
				System.out.println(" Split array ：" + Arrays.toString(ids));

				for (String id : ids) {
					list.add(id);
				}

				System.out.println(" The original set element :" + list);

				//  Control adds only three id
				if (!list.contains(idStr)) {
					//  No repeating elements 

					if (list.size() == 3) {
						//  The elements inside are equal to 3
						list.removeFirst();
					}
				} else {
					//  Contains duplicate elements 
					list.remove(idStr);

				}
				list.addFirst(idStr);

				System.out.println(" Add new id Subsequent collection elements :" + list);

				for (String id : list) {
					sb.append(id + "-");
				}

				idValues = sb.substring(0, sb.length() - 1);
				System.out.println(" After splicing histroyIDs:" + idValues);
				c.setValue(idValues);
				response.addCookie(c);

				/*
				 * // If the first visit is the same as the later one, the method will be ended directly  if
				 * (idValues.equals(idStr)){return;}
				 * 
				 * if(idValues.startsWith(idStr)){ idValues =
				 * idValues.replaceAll(idStr+"-", ""); }else{ idValues =
				 * idValues.replaceAll("-"+idStr, ""); }
				 * 
				 * 
				 * 
				 * 
				 * idValues += "-" + idStr;
				 * 
				 * System.out.println(" Now? histroyIDs:" + idValues); //
				 *  Set up cookie Value  c.setValue(idValues); response.addCookie(c);
				 */

			}

		}
	} else {
		//  Description... Was not created cookie
		Cookie cookie = new Cookie("historyIDs", idStr);
		cookie.setMaxAge(60 * 1);
		response.addCookie(cookie);
	}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {
	doGet(request, response);
}

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}

remarks : You can use string form to splice historyIds; The string format does not control the display of access history , I use it. LinkedList Set to control , The new is inserted in the first position every time you visit , All the choices LinkedList aggregate , It can control the insertion position and insertion at the beginning and end of the line , You can also delete the elements at the specified position and the first and last positions .

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