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Solve the problem that JSP cannot use session.getattribute()

2022-07-24 22:40:00 【Cyclone 1+1】

summary ,IDEA project JSP Pages cannot use built-in session Object's getAttribute() Method .

The project has already imported jsp-api.jar and servlet-api.jar, After the user logs in successfully on the login page, he saves the user object session in , It is convenient to show the relevant information of users later . But there was a problem , Cannot call directly JSP Built in session Object's getAttribute() Method get user . I don't know the specific reason , But the solution is as follows ：

1. The login page , When the user logs in successfully, he will jump to list.jsp On the page .

//  Get username 
String username = request.getParameter("username");
String password = request.getParameter("password");
String sql = "select id, username, password from t_user where username = ? and password = ?";
//  perform sql And query users 
User user = DBUtils.query(User.class, sql, username, password);
if (user != null){
    
    //  Get or create users session, Here, it is required to obtain the user's session, If not, one will be created automatically session object .
    HttpSession session = request.getSession();
    //  Store user information in session among 
    session.setAttribute("user", user);
    //  When the user is successfully queried, jump to the user list page 
    response.sendRedirect(request.getContextPath()+"/dept/list");
} else {
    
    //  No user found , Let the user rewrite the user name and password 
    response.sendRedirect(request.getContextPath()+"/login_fail.jsp");
}

2. stay jsp Login display in “ welcome ：xxx” user , The code is as follows ：

<body>
    <h3> welcome ：<%=session.getAttribute("user")%></h3>
</body>

You can't directly use built-in objects session.getAttribute() Method to take it out and save it in the login page session Users in the domain .

3. Solve the above problems

stay list.jsp Page usage request.getSession() Method to get a session object ; And then take it out session Data in the domain .

<%-- from session Remove from user--%>
<%
    User user = (User)request.getSession().getAttribute("user");
%>
<body>
    <h3> welcome ：<%=user.getUsername()%></h3>
</body>