Question

当您输入用户名时出现问题并且密码未移至页面＆＃34; welcome.jsp＆＃34;显示空白页面Beys，无论是正确还是不正确

的index.jsp

<form action="LoginServlet" method="post">
        <fieldset style="width: 300px">
            <legend> Login to App </legend>
            <table>
                <tr>
                    <td>User ID</td>
                    <td><input type="text" name="username" required="required" /></td>
                </tr>
                <tr>
                    <td>Password</td>
                    <td><input type="password" name="userpass" required="required" /></td>
                </tr>
                <tr>
                    <td><input type="submit" value="Login" /></td>
                </tr>
            </table>
        </fieldset>
    </form>

类LoginDao

public class LoginDao {

    public static boolean validate(String name, String pass) {
        boolean status = false;

        String JDBC_DRIVER = "com.mysql.jdbc.Driver";
        String DB_URL = "jdbc:mysql://localhost/iqraa";
        String USER = "root";
        String PASS = "";

        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        PreparedStatement pst = null;

        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
            pst=conn.prepareStatement("select * from user where UserName=? AND UserPassword=?");

            pst.setString(1, name);
            pst.setString(2, pass);

            rs = pst.executeQuery();
            status = rs.next();


        } catch (Exception e) {
            System.err.println(""+e);
        }

        return status;

    }
}

LoginServlet

@Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        String name = request.getParameter("username");
        String pass= request.getParameter("userpass");
        HttpSession session = request.getSession(false);
        if (session != null) {
            session.setAttribute("name", name);
       }


        if(LoginDao.validate(name,pass)){
            RequestDispatcher rd = request.getRequestDispatcher("welcome.jsp");
            rd.forward(request, response);
        }else{
           out.print("<p style=\"color:red\">Sorry username or password error</p>");
            RequestDispatcher rd = request.getRequestDispatcher("index.jsp");
            rd.include(request, response); 
        }

        out.close();

    }

的web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>servlets.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/LoginServlet</url-pattern>
    </servlet-mapping>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

Answer 1

问题在于使用请求调度程序打开输出流。

javadoc说：

应该在响应提交之前调用
forward 客户端（在刷新响应正文输出之前）。如果回应已经提交，这个方法抛出了 IllegalStateException异常。响应缓冲区中未提交的输出是在前锋之前自动清除。

试试这个：

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
    // response.setContentType("text/html");
    // PrintWriter out = response.getWriter();

    String name = request.getParameter("username");
    String pass= request.getParameter("userpass");
    HttpSession session = request.getSession(false);
    if (session != null) {
        session.setAttribute("name", name);
   }


    if(LoginDao.validate(name,pass)){
        RequestDispatcher rd = request.getRequestDispatcher("welcome.jsp");
        rd.forward(request, response);
    }else{
       out.print("<p style=\"color:red\">Sorry username or password error</p>");
        RequestDispatcher rd = request.getRequestDispatcher("index.jsp");
        rd.include(request, response); 
    }

    // out.close();

}

转换到servlet中页面的问题

1 个答案: