CategoryServlet，正如第4篇中提到的這個Servlet主要是針對Category數據的操作，包括添加，刪除，修改，更新等等。
之所以拿CategoryServlet純粹因為它比較簡單。
對于CategoryServlet的基本思路是：接收requst傳來的參數method,然后在根據method的要求來進行不同的操作。
1 protected void processRequest(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3 response.setContentType("text/html;charset=UTF-8");
4 request.setCharacterEncoding("UTF-8");
5 String method = request.getParameter("method");
6 if (method.equals("add")) {
7 add(request, response);
8 } else if (method.equals("delete")) {
9 delete(request, response);
10 } else if (method.equals("edit")) {
11 preEdit(request, response);
12 } else if (method.equals("update")) {
13 update(request, response);
14 } else if (method.equals("list")) {
15 list(request, response);
16 }
17 }
直接添加這些方法，netbeans會有無法找到對應方法的提示，
點擊黃色小燈泡，IDE自動生成對應的方法，建議在這些方法后面添加throws語句。例：
1 private void add(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3
4 }
a. add方法：接收分類名稱(category.name),QueryRunner對象根據sql命令執行update操作，request傳回結果(比如：轉到對應頁面）
1 private void add(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3 String name = request.getParameter("name");
4 String sql = "insert into category (name) values (?)";
5 String params[] = {name};
6 QueryRunner qr = DbHelper.getQueryRunner();
7 try {
8 qr.update(sql, params);
9 } catch (SQLException ex) {
10 Logger.getLogger(CategoryServlet.class.getName()).log(Level.SEVERE, null, ex);
11 }
12 list(request,response);
13 }
b. delete方法：接收分類類別(category.id),QueryRunner對象根據sql語句執行update操作，request傳回結果(比如：轉到對應頁面)
1 private void delete(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3 String id = request.getParameter("id");
4 String sql = "delete from category where id = "+id;
5
6 QueryRunner qr = DbHelper.getQueryRunner();
7 try {
8 qr.update(sql);
9 } catch (SQLException ex) {
10 Logger.getLogger(CategoryServlet.class.getName()).log(Level.SEVERE, null, ex);
11 }
12
13 list(request,response);
14 }
c. preEdit方法：接收分類類別(category.id),QueryRunner對象根據sql語句執行query操作，request傳回結果，轉入對應編輯頁面；
1 private void preEdit(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3 String id = request.getParameter("id");
4 String sql = "select id,name from category where id = "+id;
5 List categories = null;
6 Category category = null;
7
8 QueryRunner qr = DbHelper.getQueryRunner();
9 try {
10 categories = (List) qr.query(sql, new BeanListHandler(Category.class));
11 } catch (SQLException ex) {
12 Logger.getLogger(CategoryServlet.class.getName()).log(Level.SEVERE, null, ex);
13 }
14
15 if (categories != null){
16 category = (Category)categories.get(0);
17 }
18 request.setAttribute("category", category);
19 request.getRequestDispatcher("/admin/editCategory.jsp").forward(request, response);
20 }
d. update方法：接收分類名稱(name),編號(id)，QueryRunner對象根據sql語句執行update操作，request傳回結果(比如：轉到對應頁面)；
1 private void update(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3 String id = request.getParameter("id");
4 String name = request.getParameter("name");
5 String sql = "update category set name = ? where id = ?";
6 String params[] = {name,id};
7
8 QueryRunner qr = DbHelper.getQueryRunner();
9 try {
10 qr.update(sql, params);
11 } catch (SQLException ex) {
12 Logger.getLogger(CategoryServlet.class.getName()).log(Level.SEVERE, null, ex);
13 }
14 list(request,response);
15 }
e. list方法：list所有相關的分類，request傳回結果(比如：轉到對應頁面)；
1 private void list(HttpServletRequest request, HttpServletResponse response)
2 throws ServletException, IOException {
3 String sql = "select id, name from category order by name";
4 List categories = null;
5
6 QueryRunner qr = DbHelper.getQueryRunner();
7 try {
8 categories = (List) qr.query(sql, new BeanListHandler(Category.class));
9 } catch (SQLException ex) {
10 Logger.getLogger(CategoryServlet.class.getName()).log(Level.SEVERE, null, ex);
11 }
12
13 request.setAttribute("categories", categories);
14 request.getRequestDispatcher("/admin/adminCategoryList.jsp").forward(request, response);
15 }