@WebServlet("/query")
public class QueryServlet extends HttpServlet {...}

在Servlet类上写@WebServlet("query"),就相当于在配置文件里写了↓

<servlet><servlet-name>query</servlet-name><servlet-class>QueryServlet</servlet-class></servlet><servlet-mapping><servlet-name>query</servlet-name><url-pattern>/query</url-pattern></servlet-mapping>