JAVA：使用 IntelliJ IDEA 在 JSP 中显示 mysql 数据答案

【问题标题】：JAVA: Displaying mysql data in JSP using IntelliJ IDEAJAVA：使用 IntelliJ IDEA 在 JSP 中显示 mysql 数据
【发布时间】：2019-07-04 04:24:20
【问题描述】：

所以我使用 intelliJ 和 Java 作为编程语言已经快 2 个月了。我正在开发一个 Web 应用程序，并且我已经使用LoginServlet.java 成功实现了用户登录。但是我想在 JSP 中显示COUNT(*) 输出，但我在数据输出的显示方式上遇到了一些问题。我不确定我的 servlet 是否允许多个 request.getRequestDispatcher 或者我需要在 servlet 之外编写代码（可能在 jsp 中）。一些方向将不胜感激。

这是我的代码

UserLogin.java Servlet

@WebServlet("/organizer")
public class UserLogin extends HttpServlet {

@SuppressWarnings("Duplicates")
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();

    try{

        String email = request.getParameter("email");
        String password = request.getParameter("password");

        OrganizerDao e = new OrganizerDao();

        HttpSession session = request.getSession();

        session.setAttribute("email", email);

        Connection con= OrganizerDao.getConnection();
        PreparedStatement st=con.prepareStatement("select id, firstname, lastname from users where email=? and password=?");
        st.setString(1,email);
        st.setString(2,password);
        ResultSet rs=st.executeQuery();
        if (rs.next()) {

            request.setAttribute("id",rs.getInt("id"));
            request.setAttribute("firstname",rs.getString("firstname"));
            request.setAttribute("lastname",rs.getString("lastname"));

            RequestDispatcher rd = request.getRequestDispatcher("dashboard.jsp");
            rd.include(request, response);

        } else {

            out.println("<div class=\"alert alert-danger\" role=\"alert\">");
            out.println("<center>Oh snap! Change a few things and try submitting again.</center>");
            out.println("</div>");

            request.getRequestDispatcher("login.jsp").include(request, response);
        }

        con.close();

    }catch(Exception ex){ex.printStackTrace();}


}


@SuppressWarnings("Duplicates")
protected void doPost(HttpServletRequest request,
                      HttpServletResponse response) throws ServletException, IOException {

    processRequest(request,response);
    getEventsCount(request,response);
    getAffiliatesCount(request,response);

}


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

    processRequest(request,response);
    getEventsCount(request,response);
    getAffiliatesCount(request, response);

}


@SuppressWarnings("Duplicates")
protected void getEventsCount(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    //call ConnectToDatabase


    try {

        String email = request.getParameter("email");
        String password = request.getParameter("password");

        HttpSession session = request.getSession();

        session.setAttribute("email", email);


        try {

            String query = "SELECT count(events.userid) AS etotal from events, users where events.userid=users.id and users.email=? and users.password=?";
            int count = 0;

            Connection connection = EventsDAO.getConnection();
            PreparedStatement st = connection.prepareStatement(query);
            st.setString(1, email);
            st.setString(2, password);
            ResultSet rs = st.executeQuery();
            while (rs.next()) {

                count = rs.getInt("etotal");

                request.setAttribute("count", count);

                RequestDispatcher rd = request.getRequestDispatcher("dashboard.jsp");
                rd.include(request, response);

            }

        } catch (SQLException e) {
            e.printStackTrace();
        }


    }  catch (Exception ex) {
    ex.printStackTrace();
}



}


@SuppressWarnings("Duplicates")
protected void getAffiliatesCount(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    //call ConnectToDatabase


    try {

        String email = request.getParameter("email");
        String password = request.getParameter("password");

        HttpSession session = request.getSession();

        session.setAttribute("email", email);


        try {

            String query = "SELECT count(affiliates.userid) AS affiliatestotal from affiliates, users where affiliates.userid=users.id and users.email=? and users.password=?";
            int affiliatescount = 0;

            Connection connection = EventsDAO.getConnection();
            PreparedStatement st = connection.prepareStatement(query);
            st.setString(1, email);
            st.setString(2, password);
            ResultSet rs = st.executeQuery();
            while (rs.next()){

                affiliatescount = rs.getInt("affiliatestotal");

                request.setAttribute("affiliatescount",affiliatescount);

                RequestDispatcher rd = request.getRequestDispatcher("dashboard.jsp");
                rd.include(request, response);

            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }catch(Exception ex){ex.printStackTrace();}
}

}

仪表板.jsp

<div class="card card-sm">
                                <div class="card-body">
                                    <div class="d-flex justify-content-between mb-5">
                                        <div>
                                            <span class="d-block font-15 text-dark font-weight-500">My Events</span>
                                        </div>
                                        <div>
                                            <span class="text-warning font-14 font-weight-500">-2.8%</span>
                                        </div>
                                    </div>
                                    <div>
                                        <span class="d-block display-4 text-dark mb-5">${count}</span>
                                        <small class="d-block">100 Targeted</small>
                                    </div>
                                </div>
                            </div>

编辑：我还想知道是否允许使用重定向到同一页面的请求调度程序显示 3 个方法，如下面的代码所示

UserLogin.java Servlet

@SuppressWarnings("Duplicates")
protected void doPost(HttpServletRequest request,
                      HttpServletResponse response) throws ServletException, IOException {

    processRequest(request,response);
    getEventsCount(request,response);
    getAffiliatesCount(request,response);


}


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

    processRequest(request,response);
    getEventsCount(request,response);
    getAffiliatesCount(request, response);

}

更新：我能够通过使用字符串作为所有 getDispatcher 转发器的占位符来解决数据显示问题。但是错误页面现在无法正确显示。这是我的代码：

UserLogin.java

String page = "";

@SuppressWarnings("Duplicates")
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    //call ConnectToDatabase

    try{

        String email = request.getParameter("email");
        String password = request.getParameter("password");

        OrganizerDao e = new OrganizerDao();

        HttpSession session = request.getSession();

        session.setAttribute("email", email);

        Connection con= OrganizerDao.getConnection();
        PreparedStatement st=con.prepareStatement("select id, firstname, lastname from users where email=? and password=?");
        st.setString(1,email);
        st.setString(2,password);
        ResultSet rs=st.executeQuery();
        if (rs.next()) {

            request.setAttribute("id",rs.getInt("id"));
            request.setAttribute("firstname",rs.getString("firstname"));
            request.setAttribute("lastname",rs.getString("lastname"));

            //RequestDispatcher rd = request.getRequestDispatcher("dashboard.jsp");
            //rd.include(request, response);

            page = "dashboard.jsp";



        } else {

            out.println("<div class=\"alert alert-danger\" role=\"alert\">");
            out.println("<center>Oh snap! Change a few things and try submitting again.</center>");
            out.println("</div>");

            //request.getRequestDispatcher("/login.jsp").include(request, response);

            page = "/login.jsp";

        }

        con.close();

    }catch(Exception ex){ex.printStackTrace();}


}

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

    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    //call ConnectToDatabase

    processRequest(request,response);
    getEventsCount(request,response);
    getAffiliatesCount(request,response);
    getTotalWithdrawal(request, response);

    if(page!=null){

        request.getRequestDispatcher("/dashboard.jsp").include(request, response);

    }else {

        out.println("<div class=\"alert alert-danger\" role=\"alert\">");
        out.println("<center>Oh snap! Change a few things and try submitting again.</center>");
        out.println("</div>");

        request.getRequestDispatcher("/login.jsp").include(request, response);


    }
}

【问题讨论】：

标签： java mysql jsp servlets intellij-idea

【解决方案1】：

你的实现离这里很远。您需要执行以下操作。您可以使用 JSP EL 访问请求属性：

<p>Event Count is ${eventCount}</p>
<p>Affiliate Count is ${affiliateCount}</p>
<p>User Name is ${user.forename} ${user.surname}</p>

小服务程序

@WebServlet("/organizer")
public class UserLogin extends HttpServlet {

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

        doPost(request, response);
    }

    @SuppressWarnings("Duplicates")
    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response) 
         throws ServletException, IOException {

        String email = request.getParameter("email");
        String password = request.getParameter("password");
        
        User user = getUsert(emil password)

        if(user != null){
            request.setAttributes("eventCount", getEventsCount(email, password));
            request.setAttributes("affiliateCount", getAffiliatesCount(email,password));
            request.getRequestDispatcher("/dashboard.jsp").forward(request, response);
        }else{
            request.setAttribute("failedLogin", true);
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        }
    }

    protected User getUser(String email  String password){}
            
        User user = null; //create a class user with 3 fields
        
        // Query
        
        if(rs.next()){
            user = new User(rs.getInt("id"), 
                                rs.getString("firstname"), 
                                    rs.getString("lastname"))
        }
        
        return user;
    }

    protected int getEventsCount(String email, String password)
            throws ServletException, IOException {
        // query and return result
        return count;
    }

    protected void getAffiliatesCount(String email, String password)
            throws ServletException, IOException {
        // query and return result
        return count;
    }
}

【讨论】：

感谢您的帮助。非常感谢