①：使用Filter，判断用户名是否为空，为空的话返回登录画面。

1，web.xml:

1.<filter>

2.  <filter-name>SecurityServlet</filter-name>

3.  <filter-class>com.msm2.filter.MyFilter</filter-class>

4. </filter>

5.

6. <filter-mapping>

7.  <filter-name>SecurityServlet</filter-name>

8.  <url-pattern>/*</url-pattern>

9. </filter-mapping>

2，spring-mvc.xml:

1<bean id="loginController" class="com.msm2.controller.LoginController" />

2.<bean id="mainController" class="com.msm2.controller.MainController" />

3.<bean id="handlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">

4.　　<property name="mappings">

5.　　　　<props>

6.　　　　　　<prop key="login">loginController</prop>

7.　　　　　　<prop key="userLogin">mainController</prop>

8.　　　　</props>

9.　　</property>

10.</bean>

package com.msm2.filter;

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

import org.apache.log4j.Logger;

public class MyFilter extends HttpServlet implements Filter {

	private static final long serialVersionUID = 1L;

	private static final Logger LOGGER = Logger.getLogger(MyFilter.class);

	String encode = null;

	@Override

	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)

			throws IOException, ServletException {

		arg0.setCharacterEncoding(encode);

		arg1.setCharacterEncoding(encode);

	        HttpServletRequest request = (HttpServletRequest) arg0;

		HttpServletResponse response = (HttpServletResponse) arg1;

		HttpSession session = request.getSession(true);

        String url=request.getRequestURI();

        if (url.indexOf("login")<0){

        	// 不是login画面

        	System.out.println("不是login画面");

        	if (request.getParameter("userId") ==null || "".equals(request.getParameter("userId"))) {

        		// 不是login画面并且用户名为null

        		System.out.println("不是login画面并且用户名为null");

        		response.sendRedirect(request.getContextPath() + "/login");

        	} else {

        		System.out.println("不是login画面但是用户名不为null");

        		// 不是login画面但是用户名不为null

        		arg2.doFilter(arg0, arg1);

        	}

		} else {

			// login画面

			System.out.println("login画面");

			arg2.doFilter(arg0, arg1);

		}

	@Override

	public void init(FilterConfig arg0) throws ServletException {

		encode = "utf-8";

	}

}

写的虽然简单，但是初步实现了目标，以后对Filter理解的更深，再进一步记录。