@WebFilter(filterName ="ManagerFilter", urlPatterns = {"/pages/manager/*", "/manager/bookServlet"})
public class AdminFilter implements Filter {
/**
* doFilter method
*/
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain
filterChain) throws IOException, ServletException {
HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
HttpSession session = httpServletRequest.getSession();
Object user = session.getAttribute("user");
// 
if (user == null) {
servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
return;
} else {
// 
filterChain.doFilter(servletRequest,servletResponse);
}
}
}

     public void set(T value) {
         Thread t = Thread.currentThread(); //获取当前的线程
         ThreadLocalMap map = getMap(t);    //每一个线程都维护各自的一个容器（ThreadLocalMap）
         if (map != null)
             map.set(this, value);          //这里的key对应的是ThreadLocal，因为我们的组件中需要传输（共享）的对象可能会有多个（不止Connection）
         else
             createMap(t, value);           //默认情况下map是没有初始化的，那么第一次往其中添加数据时，会去初始化
     }

     public T get() {
         Thread t = Thread.currentThread(); //获取当前的线程
         ThreadLocalMap map = getMap(t);    //获取和这个线程（企业）相关的ThreadLocalMap（也就是工作纽带的集合）
         if (map != null) {
             ThreadLocalMap.Entry e = map.getEntry(this);   //this指的是ThreadLocal对象，通过它才能知道是哪一个工作纽带
             if (e != null) {
                 @SuppressWarnings("unchecked")
                 T result = (T)e.value;     //entry.value就可以获取到工具箱了
                 return result;
             }
         }
         return setInitialValue();
     }

private static ThreadLocal<Connection> conns = new ThreadLocal<>();
//  Connection conn = null;
Connection conn = conns.get();

@WebFilter(filterName ="TransactionFilter", urlPatterns = "/*")
public class TransactionFilter implements Filter {
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain
filterChain) throws IOException, ServletException {
try {
filterChain.doFilter(servletRequest,servletResponse);
JdbcUtils.commitAndClose();// 提交事务
} catch (Exception e) {
JdbcUtils.rollbackAndClose();//回滚事务
e.printStackTrace();
}
}

public abstract class BaseServlet extends HttpServlet {
try {
// 
Method method = this.getClass().getDeclaredMethod(action, HttpServletRequest.class,
HttpServletResponse.class);
// System.out.println(method);
// 
method.invoke(this, req, resp);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e);// throw new RunException Filter 
}
}

<error-page>
<!--error-code -->
<error-code>500</error-code>
<!--location-->
<location>/pages/error/error500.jsp</location>
</error-page>
<!--error-page -->
<error-page>
<!--error-code -->
<error-code>404</error-code>
<!--location -->
<location>/pages/error/error404.jsp</location>
</error-page>

//监听上下文启动，在上下文启动的时候去创建IOC容器,然后将其保存到application作用域
//后面中央控制器再从application作用域中去获取IOC容器
@WebListener
public class ContextLoaderListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        //1.获取ServletContext对象
        ServletContext application = servletContextEvent.getServletContext();
        //2.获取上下文的初始化参数
        String path = application.getInitParameter("contextConfigLocation");
        //3.创建IOC容器
        BeanFactory beanFactory = new ClassPathXmlApplicationContext(path);
        //4.将IOC容器保存到application作用域
        application.setAttribute("beanFactory",beanFactory);
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

Person person = new Person(1,"AA");
Gson gson = new Gson();
String personJsonString = gson.toJson(person);
System.out.println(personJsonString);

Person person1 = gson.fromJson(personJsonString, Person.class

List<Person> personList = new ArrayList<>();
personList.add(new Person(1, "AA"));
personList.add(new Person(2, "BB"));

Gson gson = new Gson();
// transfer to json string
String personJsonString = gson.toJson(personList);
System.out.println(personJsonString);

List<Person> list = gson.fromJson(personJsonString, new PersonListType().getType());

Map<Integer,Person> personMap = new HashMap<>()
personList.add(new Person(1, "AA"));
personList.add(new Person(2, "BB"));

Gson gson = new Gson();
// transfer to json string
String personJsonString = gson.toJson(personMap);
System.out.println(personJsonString);

Map<Integer,Person> personMap2 = gson.fromJson(personJsonString, new TypeToken<HashMap<Integer,Person>>(){}.getType());

protected void ajaxExistsUsername(HttpServletRequest req, HttpServletResponse resp) throws
ServletException, IOException {
// get username
String username = req.getParameter("username");
//  userService.existsUsername();
boolean existsUsername = userService.existsUsername(username);
// 
Map<String,Object> resultMap = new HashMap<>();
resultMap.put("existsUsername",existsUsername);
Gson gson = new Gson();
String json = gson.toJson(resultMap);
resp.getWriter().write(json);
}

$("#username").blur(function () {
//1 get username
var username = this.value;
$.getJSON("http://localhost:8080/book/userServlet","action=ajaxExistsUsername&username=" +
username,function (data) {
if (data.existsUsername) {
$("span.errorMsg").text("xxxx！");
} else {
$("span.errorMsg").text("xxxx！");
}
});
});

protected void addItem(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//        System.out.println("bookId: " + request.getParameter("id"));

        System.out.println("request head reference value: " + request.getHeader("Referer"));
//        2.1 : 获取请求的参数，商品编号
        int id = WebUtils.parseInt(request.getParameter("id"), 0);
//        2.2： 调用bookService.queryBookById(id): Book得到图书的信息
        Book book = bookService.queryBookById(id);
//        2.3： 把图书信息，转换成CartItem商品项
        CartItem cartItem = new CartItem(book.getId(), book.getName(), 1, book.getPrice(), book.getPrice());
//        2.4: 调用Cart.addItem(CartItem);添加商品项
        Cart cart = (Cart) request.getSession().getAttribute("cart");
        if (cart == null) {
            cart = new Cart();
            request.getSession().setAttribute("cart", cart);
        }
        cart.addItem(cartItem);

//        2.5: 重定向回商品列表页面
        System.out.println(cart);
        request.getSession().setAttribute("lastName", cartItem.getName());
        response.sendRedirect(request.getContextPath());

//use AJAX to add the item to the cart
Map<String,Object> resultMap = new HashMap<String,Object>();
resultMap.put("totalCount", cart.getTotalCount());
resultMap.put("lastName",cartItem.getName());
Gson gson = new Gson();
String resultMapJsonString = gson.toJson(resultMap);
resp.getWriter().write(resultMapJsonString);

    }