java - jsp无法插入数据库

Question

我无法用它插入或编辑记录。

My SQLException 有错误“无法访问 SQLException 的 catch block 。try 语句主体永远不会抛出此异常”
我是java新手，所以一切都是一个学习过程

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String forward = "";
        String action = request.getParameter("action");
        if (action.equalsIgnoreCase("delete")) {
            int surveyid = Integer.parseInt(request.getParameter("survey_id"));
            firstdao.removeFirst(surveyid);
            forward = list_first;
            try {
                request.setAttribute("firsts", firstdao.getFirst());
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else if (action.equalsIgnoreCase("edit")) {
            forward = insert_or_edit;
            int surveyid = Integer.parseInt(request.getParameter("survey_id"));
            try {
                First first = firstdao.getFirstById(surveyid);
                request.setAttribute("first", first);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else if (action.equalsIgnoreCase("listFirst")) {
            forward = list_first;
            try {
                request.setAttribute("firsts", firstdao.getFirst());
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else {
            forward = insert_or_edit;
        }
        RequestDispatcher view = request.getRequestDispatcher(forward);
        view.forward(request, response);
    }

FirstController.java

private static final long serialVersionUID = 1L;
private static String insert_or_edit = "/first.jsp";
private static String list_first = "/listfirst.jsp";
private FirstDAO firstdao; 
public FirstController() {
super();
firstdao = new FirstDAO();
}

FirstDAO.java

public void addFirst(First first) {
try {
String query = "insert into survey_data_27 (uname, p1q1, p1q2, p1q3, p1q4) values('"+ first.getuname() +"', '"+ first.getp1q1() +"', '"+ first.getp1q2() +"', '"+ first.getp1q3() +"', '"+ first.getp1q4() +"')";
Statement stmt = connection.createStatement();
stmt.executeUpdate(query);
} catch (SQLException e) {
e.printStackTrace();
}
}  

Answer 1

由于您在 DAO 类中捕获了 SQL 异常，因此它在您的 servlet 中不可见。这就是为什么你不能在那里捕获它。所以你必须删除

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

阻止您的 servlet。

您还应该使用准备好的语句。