使用Struts2拦截器如何实现一个登录验证功能

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
import com.shizongger.oa.domain.User;

public class CheckPrivilegeInterceptor extends AbstractInterceptor {

  @Override
  public String intercept(ActionInvocation invocation) throws Exception {
    System.out.println("---拦截器未拦截之前---");
    String result = invocation.invoke();
    System.out.println("---拦截器拦截之后---");
    return result;
  }
}

<!-- 配置拦截器 -->
    <interceptors>
      <!-- 声明拦截器 -->
      <interceptor name="checkPrivilege" class="com.shizongger.oa.util.CheckPrivilegeInterceptor"></interceptor>
      
      <!-- 重新定义默认的拦截器栈 -->
      <interceptor-stack name="defaultStack">
        <interceptor-ref name="checkPrivilege"></interceptor-ref>      
        <interceptor-ref name="defaultStack"></interceptor-ref>       
      </interceptor-stack>
    </interceptors>

public class MyServletContextListener implements ServletContextListener {
  
  Log log = LogFactory.getLog(this.getClass());
  
  @Autowired
  private PrivilegeService privilegeService;
  
  @Override
  public void contextDestroyed(ServletContextEvent sce) {
    log.debug("---销毁监听器---");
  }

  @Override
  public void contextInitialized(ServletContextEvent sce) {
    ServletContext sc = sce.getServletContext();
    ApplicationContext ac = WebApplicationContextUtils.getWebApplicationContext(sc);
    PrivilegeService privilegeService = (PrivilegeService) ac.getBean("privilegeServiceImpl");
    List<Privilege> topPrivilegeList = privilegeService.findTopList();
    //将权限list放到比application作用域还大的ServletContext
    sc.setAttribute("topPrivilegeList", topPrivilegeList);
    
    // 准备数据：allPrivilegeUrls
    Collection<String> allPrivilegeUrls = privilegeService.getAllPrivilegeUrls();
    sc.setAttribute("allPrivilegeUrls", allPrivilegeUrls);   
  }
}

  public String intercept(ActionInvocation invocation) throws Exception {   
    //获取信息，从session中取出当前登录用户
    User user = (User) ActionContext.getContext().getSession().get("user");
    String nameSpace = invocation.getProxy().getNamespace();
    String actionName = invocation.getProxy().getActionName();
    //对应的权限地址
    String privilegeUrl = nameSpace + actionName;
    
    //如果未登录
    if(user == null) {
      //如果是去登录的页面和登录请求，就放行
      if("/user_login".equals(privilegeUrl)) {
        return invocation.invoke();
      //否则跳转到登录页面
      } else {
        return "loginUI";
      }
    } else {
      //如果已经登录则判断是否有权限
      if(user.hasPrivilegeByUrl(privilegeUrl)) {
        return invocation.invoke();
      } else {
        return "noPrivilegeError";
      }
    }
  }

/**
 * 用户实体
 * @author shizongger
 * @date 2017/03/24
 */
public class User {
  private Log log = LogFactory.getLog(this.getClass());
  
  private Long id;
  
  private String loginName;
  
  private String password;
  
  private String name;
  
  private String gender;
  
  private String phoneNumber;
  
  private String email;
  
  private String description;
  
  private Department department;
  
  private Set<Role> roles;
  
  //getter/settter方法
  
  /**
   * 判断用户是否用该权限
   * @param privilegename 权限名称
   * @return
   */
  public boolean hasPrivilegeByName(String privilegeName) {
    log.debug("权限名称:" + privilegeName);
    
    //从本用户中取出所有角色
    for(Role role : roles) {
      //从角色遍历出所有权限
      Set<Privilege> privilegeList = role.getPrivileges();
      for(Privilege privilege : privilegeList) {
        if(privilegeName.equals(privilege.getName())) {
          log.debug(privilegeName + "---有权限---");
          return true;
        }
      }
    }
    
    log.debug(privilegeName + "---没有权限---");
    return false;
  }
  
  /**
   * 判断本用户是否有指定URL的权限
   * 
   * @param privUrl
   * @return
   */
  public boolean hasPrivilegeByUrl(String privUrl) {
    // 超级管理有所有的权限
    if (isAdmin()) {
      return true;
    }

    // >> 去掉后面的参数
    int pos = privUrl.indexOf("&#63;");
    if (pos > -1) {
      privUrl = privUrl.substring(0, pos);
    }
    // >> 去掉UI后缀
    if (privUrl.endsWith("UI")) {
      privUrl = privUrl.substring(0, privUrl.length() - 2);
    }

    // 如果本URL不需要控制，则登录用户就可以使用
    Collection<String> allPrivilegeUrls = (Collection<String>) ActionContext.getContext().getApplication().get("allPrivilegeUrls");
    if (!allPrivilegeUrls.contains(privUrl)) {
      return true;
    } else {
      // 普通用户要判断是否含有这个权限
      for (Role role : roles) {
        for (Privilege priv : role.getPrivileges()) {
          if (privUrl.equals(priv.getUrl())) {
            return true;
          }
        }
      }
      return false;
    }
  }

  /**
   * 判断本用户是否是超级管理员
   * 
   * @return
   */ 
  public boolean isAdmin() {
    return "admin".equals(loginName);
  }
}

@Service
public class PrivilegeServiceImpl extends DaoSupportImpl<Privilege> implements PrivilegeService {

  @Override
  @Transactional
  public List<Privilege> findTopList() {
    List<Privilege> topPrivletList = this.getSession()
    .createQuery("FROM Privilege p WHERE p.parent IS NULL")
    .list();
    
    return topPrivletList;
  }

  @Override
  @Transactional
  public Collection<String> getAllPrivilegeUrls() {
    return getSession().createQuery(//
        "SELECT DISTINCT p.url FROM Privilege p WHERE p.url IS NOT NULL")//
        .list();
  }

}