如何在JSP中初始化会话并正确使用它们？

我在Spring MVC应用程序中有以下文件：login.jsp、HomeController.java和DatabaseService.java。当有人在login.jsp中单击登录按钮时，它会将数据（用户名和密码）传输到HomeController.java，然后HomeController.java调用DatabaseService.java并使用一些条件从中获取响应，最后将响应返回到login.jsp。到目前为止，用户名和密码字段无效是可以的。login.jsp中的用户名和密码与存储的用户名和密码匹配时出现问题。 问题是，没有数据存储到会话变量/对象中。我试过几种方法：

public String dblogin(String username, String password) throws SQLException {
    String response = "";
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs;
    String pass = "", fname = "", lname = "";
    int userid = 0;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bloodspring", "root", "");
        stmt = conn.createStatement();
        try {
            String query = "SELECT user_id, user_fname, user_lname, pword FROM bld_user WHERE uname='"+ username +"'";
            rs = stmt.executeQuery(query);
            int res = 0;
            while( rs.next() ) {
                res++;
                pass = rs.getString("pword");
                fname = rs.getString("user_fname");
                lname = rs.getString("user_lname");
                userid = rs.getInt("user_id");
            }
            if( res == 0 ) {
                response = "Invalid Username";
            } else {
                //String new_pass = crypt.encryption(password);
                if( crypt.encryption(password).compareTo(pass) != 0 ) {
                    response = "Invalid username and/or password";
                    //response = "Original :" + pass + " :::: new : " + crypt.encryption(password);
                } else {
                    HttpServletRequest request;
                    HttpSession session = request.getSession();
                    session.setAttribute("fname", fname);
                    session.setAttribute("lname", lname);
                    session.setAttribute("username", username);
                    session.setAttribute("userid", userid);
                    response = "Login Successful";
                }
            }
        } catch( SQLException Ex) {
            Ex.printStackTrace();
            response = "Sorry something goes wrong with your MySQL query or server";
        }
    } catch( ClassNotFoundException E) {
        E.printStackTrace();
        response = "Sorry no MySQL class found";
    }
    return response;
}

但它显示了一些与空指针异常相关的错误。显示更改代码，如下所示：

public String dblogin(String username, String password) throws SQLException {
    String response = "";
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs;
    String pass = "", fname = "", lname = "";
    int userid = 0;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bloodspring", "root", "");
        stmt = conn.createStatement();
        try {
            String query = "SELECT user_id, user_fname, user_lname, pword FROM bld_user WHERE uname='"+ username +"'";
            rs = stmt.executeQuery(query);
            int res = 0;
            while( rs.next() ) {
                res++;
                pass = rs.getString("pword");
                fname = rs.getString("user_fname");
                lname = rs.getString("user_lname");
                userid = rs.getInt("user_id");
            }
            if( res == 0 ) {
                response = "Invalid Username";
            } else {
                //String new_pass = crypt.encryption(password);
                if( crypt.encryption(password).compareTo(pass) != 0 ) {
                    response = "Invalid username and/or password";
                    //response = "Original :" + pass + " :::: new : " + crypt.encryption(password);
                } else {
                    HttpServletRequest request = null;
                    try {
                        HttpSession session = request.getSession();
                        session.setAttribute("fname", fname);
                        session.setAttribute("lname", lname);
                        session.setAttribute("username", username);
                        session.setAttribute("userid", userid);
                        response = "Login Successful";
                        //response = fname + " " + lname;
                    } catch( java.lang.NullPointerException lex ) {
                        lex.printStackTrace();
                        response = "Something Wrong";
                    }
                }
            }
        } catch( SQLException Ex) {
            Ex.printStackTrace();
            response = "Sorry something goes wrong with your MySQL query or server";
        }
    } catch( ClassNotFoundException E) {
        E.printStackTrace();
        response = "Sorry no MySQL class found";
    }
    return response;
}

public String dblogin(String username, String password) throws SQLException {
    String response = "";
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs;
    String pass = "", fname = "", lname = "";
    int userid = 0;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bloodspring", "root", "");
        stmt = conn.createStatement();
        try {
            String query = "SELECT user_id, user_fname, user_lname, pword FROM bld_user WHERE uname='"+ username +"'";
            rs = stmt.executeQuery(query);
            int res = 0;
            while( rs.next() ) {
                res++;
                pass = rs.getString("pword");
                fname = rs.getString("user_fname");
                lname = rs.getString("user_lname");
                userid = rs.getInt("user_id");
            }
            if( res == 0 ) {
                response = "Invalid Username";
            } else {
                //String new_pass = crypt.encryption(password);
                if( crypt.encryption(password).compareTo(pass) != 0 ) {
                    response = "Invalid username and/or password";
                    //response = "Original :" + pass + " :::: new : " + crypt.encryption(password);
                } else {
                    HttpServletRequest request = null;
                    try {
                        response = fname + " " + lname;
                    } catch( java.lang.NullPointerException lex ) {
                        lex.printStackTrace();
                        response = "Something Wrong";
                    }
                }
            }
        } catch( SQLException Ex) {
            Ex.printStackTrace();
            response = "Sorry something goes wrong with your MySQL query or server";
        }
    } catch( ClassNotFoundException E) {
        E.printStackTrace();
        response = "Sorry no MySQL class found";
    }
    return response;
}

但它返回的响应是“有问题”[catch block of java.lang.NullPointerException]。如果我按以下方式更改代码：

public String dblogin(String username, String password) throws SQLException {
    String response = "";
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs;
    String pass = "", fname = "", lname = "";
    int userid = 0;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bloodspring", "root", "");
        stmt = conn.createStatement();
        try {
            String query = "SELECT user_id, user_fname, user_lname, pword FROM bld_user WHERE uname='"+ username +"'";
            rs = stmt.executeQuery(query);
            int res = 0;
            while( rs.next() ) {
                res++;
                pass = rs.getString("pword");
                fname = rs.getString("user_fname");
                lname = rs.getString("user_lname");
                userid = rs.getInt("user_id");
            }
            if( res == 0 ) {
                response = "Invalid Username";
            } else {
                //String new_pass = crypt.encryption(password);
                if( crypt.encryption(password).compareTo(pass) != 0 ) {
                    response = "Invalid username and/or password";
                    //response = "Original :" + pass + " :::: new : " + crypt.encryption(password);
                } else {
                    HttpServletRequest request = null;
                    try {
                        HttpSession session = request.getSession();
                        session.setAttribute("fname", fname);
                        session.setAttribute("lname", lname);
                        session.setAttribute("username", username);
                        session.setAttribute("userid", userid);
                        response = "Login Successful";
                        //response = fname + " " + lname;
                    } catch( java.lang.NullPointerException lex ) {
                        lex.printStackTrace();
                        response = "Something Wrong";
                    }
                }
            }
        } catch( SQLException Ex) {
            Ex.printStackTrace();
            response = "Sorry something goes wrong with your MySQL query or server";
        }
    } catch( ClassNotFoundException E) {
        E.printStackTrace();
        response = "Sorry no MySQL class found";
    }
    return response;
}

public String dblogin(String username, String password) throws SQLException {
    String response = "";
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs;
    String pass = "", fname = "", lname = "";
    int userid = 0;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bloodspring", "root", "");
        stmt = conn.createStatement();
        try {
            String query = "SELECT user_id, user_fname, user_lname, pword FROM bld_user WHERE uname='"+ username +"'";
            rs = stmt.executeQuery(query);
            int res = 0;
            while( rs.next() ) {
                res++;
                pass = rs.getString("pword");
                fname = rs.getString("user_fname");
                lname = rs.getString("user_lname");
                userid = rs.getInt("user_id");
            }
            if( res == 0 ) {
                response = "Invalid Username";
            } else {
                //String new_pass = crypt.encryption(password);
                if( crypt.encryption(password).compareTo(pass) != 0 ) {
                    response = "Invalid username and/or password";
                    //response = "Original :" + pass + " :::: new : " + crypt.encryption(password);
                } else {
                    HttpServletRequest request = null;
                    try {
                        response = fname + " " + lname;
                    } catch( java.lang.NullPointerException lex ) {
                        lex.printStackTrace();
                        response = "Something Wrong";
                    }
                }
            }
        } catch( SQLException Ex) {
            Ex.printStackTrace();
            response = "Sorry something goes wrong with your MySQL query or server";
        }
    } catch( ClassNotFoundException E) {
        E.printStackTrace();
        response = "Sorry no MySQL class found";
    }
    return response;
}

然后它会正常工作，并从数据库返回名字，姓氏。因此，我认为我的代码不适用于会话。

---

谁能告诉我如何将数据库中的数据存储到会话中。

您可以使用spring security进行身份验证。除此之外，您还可以按照下面的代码段进行操作。请注意，您实际上不需要在会话中单独存储所有字段。将用户对象存储到会话中所需的一切

@RequestMapping(value = "login.html", method = RequestMethod.POST)
            public ModelAndView post(@ModelAttribute("login") LoginEntity login, HttpServletRequest req) {


    /*    CHECK IN DATABASE if the user name and password matches or not */
    UserObject userObject=dblogin(login.userName,login.password);


    if(userObject!=null){
        HttpSession session = req.getSession(true);
        session.setAttribute("user",userObject);
    }
    else
       return new ModelAndView("login");
    }

---

是否需要自己构建身份验证？如果没有，请尝试spring security。关于npe：它被扔到哪里？显示堆栈跟踪。您正在对空请求对象调用getSession（）是最早使用的。我写了那些代码。但是它不起作用。@Shimul你试过答案了吗？它应该起作用