public class LoginInterceptor implements Interceptor {

 private Map<String,Object> session = null;
 public void destroy() { }
 public void init() { }
 public String intercept(ActionInvocation actionInvocation) throws Exception {
 8　　　　　Object myAction = actionInvocation.getAction();
  if(myAction instanceof UserAction){
   System.out.println("你访问的Action是UserAction,不要校验Session，否则死循环");
   //放行
   return actionInvocation.invoke();
  }else{
   System.out.println("你访问的Action是："+myAction);
  }

  session = ActionContext.getContext().getSession();
  Object user = session.get("user");
  if (user!=null){
   return actionInvocation.invoke();
  }else{
   return "login";
  }

}

注：该方法可以不加：<param name="excludeMethods">loginView,login</param>

public class LoginInterceptor extends MethodFilterInterceptor {
 private Map<String,Object> session = null;
 protected String doIntercept(ActionInvocation actionInvocation) throws Exception {
  /*
  Object myAction = actionInvocation.getAction();
  if(myAction instanceof UserAction){
   System.out.println("你访问的Action是UserAction,不要校验Session，否则死循环");
   //放行
   return actionInvocation.invoke();
  }else{
   System.out.println("你访问的Action是："+myAction);
  }
  */
  session = ActionContext.getContext().getSession();
  Object user = session.get("user");
  if (user!=null){
   return actionInvocation.invoke();
  }else{
   return "login";
  }
 }
}

public class UserAction extends ActionSupport implements ModelDriven<User>,SessionAware{

 private Map<String,Object> session = null;
 private User user = null;
　　　//驱动模型
 public User getModel() {
  this.user = new User();
  return this.user;
 }

 public void setSession(Map<String, Object> map) {
  this.session = map;
 }

 public String loginView(){
  return "loginViewSuccess";
 }

 public String login(){
  if ("admin".equals(user.getUserName())&&"123456".equals(user.getUserPassword())){
   session.put("user",user);
   return this.SUCCESS;
  }else{
   return this.ERROR;
  }

 }
}

<struts>
 <package name="myPackage" extends="struts-default">

  <interceptors>

   <interceptor name="loginInterceptor" class="com.nf.action.LoginInterceptor"></interceptor>
   <interceptor-stack name="myStack">
    <interceptor-ref name="loginInterceptor">
     <!--excludeMethods需要生效的话，自定义的拦截器，不能使用实现Interceptor接口，而是extends MethodFilterInterceptor-->
     <param name="excludeMethods">loginView,login</param><!--不用此行时 我们可以配合①使用拦截器-->
    </interceptor-ref>
    <interceptor-ref name="defaultStack"></interceptor-ref>
   </interceptor-stack>
  </interceptors>
  <!--配置一个默认拦截器，也就是所有的Action都必须使用-->
  <default-interceptor-ref name="myStack"/>
  <global-results>
   <result name="login" type="redirectAction">userAction_loginView</result>
  </global-results>
  <!--不写method，默认就是execute-->
  <action name="indexAction" class="com.nf.action.IndexAction" method="execute">
   <result name="success">/WEB-INF/jsp/index.jsp</result>
   <!--
   <interceptor-ref name="myStack"></interceptor-ref>
   -->
   <!--注释这里也可以放该代码 只不过每一个action都要放比较麻烦 
   <interceptor-ref name="loginInterceptor"></interceptor-ref>
   <interceptor-ref name="defaultStack"></interceptor-ref>
   -->
  </action>

  <action name="otherFunctionAction" class="com.nf.action.OtherFunctionAction">
   <!--不写name，默认就是success-->
   <result>/WEB-INF/jsp/otherFunction.jsp</result>
  </action>
  
  <action name="userAction_*" class="com.nf.action.UserAction" method="{1}">
   <result name="loginViewSuccess">/WEB-INF/jsp/loginView.jsp</result>
   <result name="error">/WEB-INF/jsp/error.jsp</result>
   <result name="success" type="redirectAction">indexAction</result>
   <allowed-methods>login,loginView</allowed-methods>
  </action>
 </package>
</struts>