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java - 请求结束后请求属性未清除

转载 作者：太空宇宙 更新时间：2023-11-04 14:45:24 25 4
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我的 jsp 中的请求属性有问题，我正在使用 mvc 模式并设置请求属性并从 servlet 转发到 jsp。该应用程序是一个银行应用程序，目标是使用客户 id 来获取客户，通过客户 id 将其传递给 Account 类来收集用户的所有帐户。我已经解决了这个问题，我可以毫无问题地获取帐户信息并进行处理。我遇到的问题是，当我关闭页面并从头开始再次运行时，我发现当我到达表时，它仍然放入前一个请求中的信息以及我请求的新信息。像这样:

(First Run)

second Run

我的代码如下，用于将我定向到 jsp 的 servlet 以及我在其中使用信息的 jsp。

AccountServlet.java:

package com.ChattBank.controller;

import com.ChattBank.business.Account;
import com.ChattBank.business.Accounts;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 *
 * @author AARONS
 */
public class AccountServlet 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");
    try (PrintWriter out = response.getWriter()) {
        /* 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 AccountServlet</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet AccountServlet at " + request.getContextPath() + "</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}

// <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 {
    //HttpSession session = request.getSession();
    String action = request.getParameter("action");

        if (action == null) {
            request.getRequestDispatcher("/Welcome.jsp").forward(request, response);
        } else if (action.equals("view")) {
            Accounts acct = new Accounts();
            ArrayList<Account> list = new ArrayList();
            try {
                acct.setCustAccounts(request.getParameter("id"));
                list.addAll(acct.getCustAccounts());
                System.out.println(request.getParameter("id"));
            } catch (SQLException ex) {
                Logger.getLogger(Accounts.class.getName()).log(Level.SEVERE, null, ex);
            }

            request.setAttribute("acctList", list);
                request.getServletContext().getRequestDispatcher("/accounts.jsp").forward(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 {
    String action = request.getParameter("action");
    String custId = request.getParameter("custID");

    if (action == null) {
        request.getRequestDispatcher("/Welcome.jsp").forward(request, response);
    }
}

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

}

accounts.jsp:

<%-- 
    Document   : accounts
    Created on : Jun 25, 2014, 12:24:38 AM
    Author     : Richard Davy
--%>
<%@page import="java.util.ArrayList"%>
<%@page import="com.ChattBank.business.Account"%>
<%@page import="com.ChattBank.business.Accounts"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Your Accounts</title>
    </head>
    <body>
       <% 
            ArrayList<Account> list = new ArrayList();

            list.addAll((ArrayList)request.getAttribute("acctList"));

            for (Account custAccount : list) {
                System.out.println("From JSP: " + custAccount.getCustId() + " " + custAccount.getAcctNo() + " " + custAccount.getAcctType() + " " + custAccount.getBalance());
                System.out.println("Getting Object From Section");
            }        
        %>

        <h1>You Made It Here!</h1>
        <table border="1" width="2" cellspacing="5" cellpadding="2">
            <thead>
                <tr>
                    <th colspan="10">Your Chatt Accounts</th>
                </tr>
            </thead>
            <tbody>
                <% for (int i = 0; i < list.size(); i++){ %>
                <tr>
                    <td colspan="2">Account: </td>
                    <td colspan="2"><%= list.get(i).getCustId() %></td>
                    <td colspan="2"><%= list.get(i).getAcctNo() %></td>
                    <td colspan="2"><%= list.get(i).getAcctType() %></td>
                    <td colspan="2"><%= list.get(i).getBalance() %></td>
                </tr>
                <% } %>
                <% list.clear(); %>
            </tbody>
        </table>
            <p>Thank you for your business!</p>

    </body>
</html>

我不太确定发生了什么，我从 session 属性开始，并认为这是我的问题，所以我转向使用请求属性。但我仍然面临同样的问题。我的印象是请求属性仅根据该请求持续，但似乎该信息仍在传递。有什么建议么？

最佳答案

这个问题的有趣之处在于它与请求属性变量无关。由于我正在实例化类中的对象列表，因此该对象列表将持续存在并且只是被添加到其中。我认为这主要是因为我使用的是可以附加的 ArrayList。我没有重写整个类来解决一些问题，而是添加了一个 try{}finally{} 语句，如下所示:

package com.ChattBank.controller;

    import com.ChattBank.business.Account;
    import com.ChattBank.business.Accounts;
    import java.io.IOException;
    import java.io.PrintWriter;
    import java.sql.SQLException;
    import java.util.ArrayList;
    import java.util.logging.Level;
    import java.util.logging.Logger;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;

    /**
     *
     * @author AARONS
     */
    public class AccountServlet 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");
        try (PrintWriter out = response.getWriter()) {
            /* 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 AccountServlet</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet AccountServlet at " + request.getContextPath() + "</h1>");
            out.println("</body>");
            out.println("</html>");
        }
    }

    // <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 {
        //HttpSession session = request.getSession();
        String action = request.getParameter("action");

            if (action == null) {
                request.getRequestDispatcher("/Welcome.jsp").forward(request, response);
            } else if (action.equals("view")) {
                Accounts acct = new Accounts();
                ArrayList<Account> list = new ArrayList();
                try {
                    acct.setCustAccounts(request.getParameter("id"));
                    list.addAll(acct.getCustAccounts());
                    System.out.println(request.getParameter("id"));

                    //This was moved into the try block itself
                    request.setAttribute("acctList", list);
               request.getServletContext().getRequestDispatcher("/accounts.jsp").forward(request, response);
                } catch (SQLException ex) {
                    Logger.getLogger(Accounts.class.getName()).log(Level.SEVERE, null, ex);

                //This is the added finally statement with the clearAccounts method
                } finally {
                   acct.clearAccounts();
                }


            } 

        }

    /**
     * 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 {
        String action = request.getParameter("action");
        String custId = request.getParameter("custID");

        if (action == null) {
            request.getRequestDispatcher("/Welcome.jsp").forward(request, response);
        }
    }

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

    }

Accounts 类中的清除帐户方法非常非常简单:

  /**
   * Clears the current array list of accounts 
   */
public void clearAccounts(){
    this.custAccounts.clear();
}

关于java - 请求结束后请求属性未清除，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24443351/

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