Question

我有点麻烦试图让这个工作。这个想法是，每次刷新页面时都会向上计数。我认为它与不可变对象有关，但我想用一个来获得不可变/可变对象的经验。

问题在于它只计算一次，然后它会停止向上计数......我似乎无法弄清楚究竟是什么导致它失败......

（我正在使用NetBeans来开发它，因此有任何奇怪的评论）

来源：

/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package Question1;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 *
 * @author Owner
 */
@WebServlet(name = "EX02W03", urlPatterns = {"/EX02W03"})
public class Q1Servlet extends HttpServlet {

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            HttpSession session = request.getSession(); 

            /* TODO output your page here. You may use following sample code. */
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet EX02W03</title>");            
            out.println("</head>");
            out.println("<body>");

            //create immutable object
            Integer add = 1;

            //create mutable object 
            Counter count = new Counter(add);

            //check to see if the session exists (if it is the users first time)
            if (session.getAttribute("timesLoggedIn") == null) {

               count.increment();               
               out.println("<h1>This is your first visit!</h1>");
               session.setAttribute("timesLoggedIn", count.getCounter());

            }else{

                count.increment();
                out.println("<h1>You have visited this page " + count.getCounter() + " times! </h1>");
                session.setAttribute("timesLoggedIn", count.getCounter());
            }


            out.println("</body>");
            out.println("</html>");


        } finally {
            out.close();
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}

柜台类：

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package Question1;

/**
 *
 * @author Owner
 */
class Counter {

    private int count; 

    public Counter(int counts) {
        count = counts;
    }


    public int getCounter(){
        return count;    
    }

    public void increment(){
        count++;

    }




}

**已修复 - 我修复了这个问题，放置了两个不可变/可变对象，它们将在“受保护的void processrequest ...”之前发布。

Answer 1

创建一个过滤器（这样就不会复制并粘贴到每个servlet上），然后使用静态（http://www.caveofprogramming.com/frontpage/articles/java/java-for-beginners-static-variables-what-are-they/）int。

public class urlFilter implements Filter {

@Override
public void init(FilterConfig config) throws ServletException {
}

@Override
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws ServletException, IOException {

myStaticVariable ++;    
}

@Override
public void destroy() {
}

}

然后在web.xml上

<filter>
    <filter-name>urlRewriteFilter</filter-name>
    <filter-class>com.example.UrlRewriteFilter</filter-class>
</filter>
<filter-mapping>
   <filter-name>urlFilter</filter-name>
   <url-pattern>/*</url-pattern>
</filter-mapping>

Answer 2

在重新加载/刷新页面时创建新的Counter对象，因此它不会增加。下面的方法只是实现你正在尝试的另一种方法。

        if (session.getAttribute("timesLoggedIn") == null) {

           out.println("<h1>This is your first visit!</h1>");
           session.setAttribute("timesLoggedIn", 1);

        }else{

            int i = Integer.parseInt(session.getAttribute("timesLoggedIn"));
            out.println("<h1>You have visited this page " + i + " times! </h1>");
            session.setAttribute("timesLoggedIn", i+1);
        }

计算每个客户端的访问次数

2 个答案: