页面显示：

失败：

成功

视图层（view）

login.html
<!DOCTYPE  HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>登陆</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
   <form action='/day04/LoginServlet' method='post'>
       <table border="1" align="center">
           <caption>用户登陆【mvc】</caption>
           <tr>
               <th>用户</th>
               <td><input type="text" name="username"></td>
           </tr>
           <tr>
           <td colspan="2" align="center">
              <input type="submit" value="提交">
           
           </td>
           </tr>
       </table>
   
   
   </form>  
  </body>
</html>

fail.hmtl
<!DOCTYPE  HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>登陆</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
   登陆失败
  </body>
</html>

cuccess.html
<!DOCTYPE  HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>登陆</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
   登陆成功  
  </body>
</html>

控制层(controller)

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet {

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// 取得提交的参数
		String username = request.getParameter("username");

		// 调用模型层对象
		LoginBean lgin = new LoginBean();
		boolean flag = lgin.validate(username);

		// 根据还回值转发到不同页面；
		if (flag) {
			// 也可以使用这个
			// this.getServletContext().getRequestDispatcher("/success.html").forward(request, response);
            //获取提交值
			ServletContext context = this.getServletContext();
			// 定位需要转发的路径
			RequestDispatcher rd = context
					.getRequestDispatcher("/success.html");
			// 真正转向页面
			rd.forward(request, response);
		} else {
			
			//this.getServletContext().getRequestDispatcher("/fail.html").forward(request, response);
			//获取提交值
			ServletContext context = this.getServletContext();
			// 定位需要转发的路径
			RequestDispatcher rd = context
					.getRequestDispatcher("/fail.html");
			// 真正转向页面
			rd.forward(request, response);
		}

	}

}

模型(model)

public class LoginBean {
	
	public boolean validate(String username)
	{
		boolean flag = false;
		//去掉空格
		if(username.trim() != null && "liwen".equals(username.trim()))
		{
			flag = true;
		}
		
		return flag;
	}

}