Question

我正在servlet中创建一个名为讨论论坛的项目...... 但我坚持在查询中从给定主题的数据库中获取结果... 我创建了一个名为index的servlet，其中有一个主题，当我点击主题时我遇到了一些错误，例如MessageDisplayed servlet中的'strong>未知列'pepsi'在'where子句' ...我认为查询中存在问题... 索引servlet的编码是：

@WebServlet("/Index")
public class Index extends HttpServlet {
    private static final long serialVersionUID = 1L;
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String url = "jdbc:mysql://localhost:3306/df";
        String driver = "com.mysql.jdbc.Driver";
        String USER = "root";
        String PASS = "root";
        try {
            Class.forName(driver);
            Connection conn = (Connection) DriverManager.getConnection(url, USER, PASS);
            out.print("<html><body>");
            out.print("<a href='PostTopic'><input type='submit' value='Post New Topic'></a><br><br>");
            String sql = "select topic_name from topic";
            PreparedStatement ps = conn.prepareStatement(sql);
            ResultSet rs = ps.executeQuery();
            while(rs.next()){
                String topic_name = rs.getString("topic_name");
                HttpSession session = request.getSession();
                session.setAttribute("topic_name", topic_name);

                out.print("<a href='MessageDisplayed'>");
                out.print(topic_name);out.print("</a>");
                out.print("<br>");
            }

            out.print("</body></html>");


        } catch (Exception e) {
            out.print(e.getMessage());
        }
        out.close();
    }

}

并且MessageDisplayed servlet的编码是：

public class MessageDisplayed extends HttpServlet {
    private static final long serialVersionUID = 1L;
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
         String url = "jdbc:mysql://localhost:3306/df";
         String driver = "com.mysql.jdbc.Driver";
         String USER = "root";
         String PASS = "root";
        try{
            Class.forName(driver);
            Connection conn = (Connection) DriverManager.getConnection(url, USER, PASS);
            HttpSession session = request.getSession();
            String topic = (String) session.getAttribute("topic_name");
            String sql = "select user_name,comment from comments where topic_name="+topic;
            PreparedStatement ps = conn.prepareStatement(sql);
        //  ps.setString(1, topic);
            ResultSet rs = ps.executeQuery();
            while(rs.next()){
                String name = rs.getString("user_name");
                String comment = rs.getString("comment");
                out.print("<html><body>");
                out.print("Name : "+name);out.print("<br>");out.print("Message : "+comment);out.print("<br>");
                out.print("</body></html>");
            }
        }
        catch(Exception e){
            out.print(e.getMessage());
        }
        out.close();
    }

}

数据库有2个表主题表（topic_id，topic_name）和一个注释表（comment_id，comment，user_name，topic_id）插入工作正常... 但我无法取得结果请尽快帮帮我....

Answer 1

我认为错误就在这一行

String sql = "select user_name,comment from comments where topic_name="+topic;

此外，您使用的方式不是使用PreparedStatement的正确方法。

使用这种方式

PreparedStatement ps = conn.prepareStatement("select user_name,comment from comments where topic_name=?");
ps.setString(1,topic);

坚持创建查询以从数据库中获取结果？

1 个答案: