First of all I'm new to JSP and trying out some projects

Please I have a jsp form that would be submited to a database here is the form code:

                        ...<form action="process/insert_category" method="post">
                            <div class="row" >
                                <div class="col-12">
                                    <h5 class="form-title"><span>Book-Category Information</span></h5>
                                </div>

                                 <div class="col-12 col-sm-6">
                                    <div class="form-group">
                                        <label>Category Name</label>
                                        <input type="text" name="categoryname" class="form-control">
                                    </div>
                                </div>
                                <div class="col-12">
                                    <button type="submit" class="btn btn-primary">Submit</button>
                                </div>
                            </div>
                        </form>...

for the category name I have to get the name=categoryname to submit as a parameter to at the back end

Here is the servlet code:

protected void InsertCategory(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {

            String categoryname = request.getParameter("categoryname");

            Category category = new Category(categoryname);
            if (!(ada.checkCategory(categoryname))) {
                if (ada.insert_category(category) > 0) {
                    request.setAttribute("success", "Category Added Successfully");
                    response.sendRedirect("../book-categories");

                } else {
                    request.setAttribute("error", "Category Not Added Successfully");
                    response.sendRedirect("../add-book-category");

                }
            } else {
                request.setAttribute("error", "Category already exists");
                response.sendRedirect("../add-book-category");
            }
        }
    }

URL PATTERN IN web.xml was:/process/*

public class adminControllerServlet extends HttpServlet {

    AdminDataAccess ada = new AdminDataAccess();    
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
            response.setContentType("text/html;charset=UTF-8");
            try (PrintWriter out = response.getWriter()) {
                String path = request.getPathInfo();
    
                // out.print(path);
                switch (path) {
    
                    ...
                    case "/insert_category":
                        InsertCategory(request, response);
                        break;
                }
    
            }
        }

Below is the database query:

   // Insert Queries
    public int insert_category(Category category) {
        int inserted = 0;
        try {
            Connection connect = con.getConnection();
            String query = "INSERT INTO Category (category_name) values(?)";
            PreparedStatement ps = connect.prepareStatement(query);
            ps.setString(1, category.getCategory_name());

            inserted = ps.executeUpdate();
        } catch (SQLException ex) {
             Logger.getLogger(AdminDataAccess.class.getName()).log(Level.SEVERE, null, ex);
        }
        return inserted;
    }

The problem I have now is when I run the project to insert a new category into the list of categories in the database after inputting the right parameters into the input field I end up with this exception:

Severe:   com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'category_name' cannot be null
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1040)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4120)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4052)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2503)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2664)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2794)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2458)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2375)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2359).....

please what else can I do because I believe request.getParameter("categoryname") ought to have gotten the data in the form input field

CodePudding user response：

I solve the issue.

The problem was my code did not have a constructor Category(categoryname) in the model package.

That made it impossible for

Category category = new Category(categoryname);

to work.

So, it simply means I was not getting any categoryname at first using getCategoryname() which was meant to be passed to the database insert statement, Causing the exception.