1. 三种创建方式

1.1. 方式1：实现Servlet接口

public class MyServlet implements Servlet {

    @Override
    public void init(ServletConfig config) throws ServletException {

    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        System.out.println("hello");
    }

    @Override
    public String getServletInfo() {
        return null;
    }

    @Override
    public void destroy() {

    }
}

1.2. 方式2：继承GenericServlet

public class MyServlet extends GenericServlet {
    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        System.out.println("hello");
    }
}

1.3. 方式3：继承HttpServlet

public class MyServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("hello");
    }
}