servlet xml 原理

如下一个方法

public class loginwindows extends HttpServlet
{
    //响应客户端请求的方法
    public void service(HttpServletRequest request,
                        HttpServletResponse response)
            throws ServletException,java.io.IOException
    {
        String errMsg = "";
        //Servlet本身并不输出响应到客户端，因此必须将请求转发
        RequestDispatcher rd;
        //获取请求参数
        String username = request.getParameter("username");
        String pass = request.getParameter("pass");

        try
        {
            //Servlet本身，并不执行任何的业务逻辑处理，它调用JavaBean处理用户请求


            if (username.equals("admin")&&pass.equals("123")) {
                //获取session对象
                HttpSession session = request.getSession(true);
                //设置session属性，跟踪用户会话状态
                session.setAttribute("name", username);
                //获取转发对象
                rd = request.getRequestDispatcher("/welcome.jsp");
                //转发请求
                rd.forward(request, response);
            }
            else
            {
                //用户名和密码不匹配时
                errMsg += "Password is wrong";
            }

        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        //如果出错，转发到重新登录
        if (errMsg != null && !errMsg.equals(""))
        {
            rd = request.getRequestDispatcher("/index.jsp");
            request.setAttribute("err" , errMsg);
            rd.forward(request,response);
        }
    }
}

然后xml文件

<servlet>
        <servlet-name>ddd</servlet-name>
        <servlet-class>xf.web.loginwindows</servlet-class>

    </servlet>
    <servlet-mapping>
        <servlet-name>ddd</servlet-name>
        <url-pattern>/ddd</url-pattern>
    </servlet-mapping>

原理就是以下四步

http://localhost:8080/ddd
-> ddd
-> ddd
-> xf.web.loginwindows