在用户进行操作前先判断用户是否登录----拦截器inceptor的用法

拦截器

java里的拦截器是动态拦截Action调用的对象，它提供了一种机制可以使开发者在一个Action执行的前后执行一段代码，也可以在一个Action执行前阻止其执行，同时也提供了一种可以提取Action中可重用部分代码的方式。在AOP中，拦截器用于在某个方法或者字段被访问之前，进行拦截。然后再之前或者之后加入某些操作。
主流的是spring的拦截器。

spring拦截器

如果使用了spring，可以直接继承HandlerInterceptor抽象接口来实现自己的拦截器。

@Component
public class AlphaInterceptor implements HandlerInterceptor {

    // logger
    private static final Logger logger = LoggerFactory.getLogger(AlphaInterceptor.class);

    // execute before Controller
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        logger.debug("preHandle: " + handler.toString());
        return true;
    }

    // execute after Controller, but before TemplateEngine
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
        logger.debug("postHandle: " + handler.toString());
    }

    // execute after TemplateEngine
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
        logger.debug("afterHandle: " + handler.toString());
    }
}

配置拦截器的config

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    @Autowired
    private AlphaInterceptor alphaInterceptor;

    @Autowired
    private LoginTicketInterceptor loginTicketInterceptor;

    @Autowired
    private LoginRequireInterceptor loginRequireInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(alphaInterceptor)
                // don't handle those static resources
                .excludePathPatterns("/**/*.css","/**/*.js","/**/*.png","/**/*.jpg","/**/*.jpeg")
                // 访问哪个页面时启用拦截器
                .addPathPatterns("/register", "/login");

        registry.addInterceptor(loginTicketInterceptor)
                .excludePathPatterns("/**/*.css","/**/*.js","/**/*.png","/**/*.jpg","/**/*.jpeg");

        registry.addInterceptor(loginRequireInterceptor)
                .excludePathPatterns("/**/*.css","/**/*.js","/**/*.png","/**/*.jpg","/**/*.jpeg");
    }
}

新建元注解

除了在拦截器中使用addPathPatterns来控制对那个页面使用拦截器外，还可以使用元注解的方式

// 新建一个元注解
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface LoginRequired {
	
}

在需要判断是否登录的方法上加上@LoginRequired注解

应用

// HostHolder.java
/**
 * hold user object by a thread isolated method
 */
@Component
public class HostHolder {

    private ThreadLocal<User> users = new ThreadLocal<>();

    public void setUser(User user){
        users.set(user);
    }

    public User getUser(){
        return users.get();
    }

    public void clear(){
        users.remove();
    }
}

// LoginTicketInterceptor.java
@Component
public class LoginTicketInterceptor implements HandlerInterceptor {

    @Autowired
    private UserService userService;

    @Autowired
    private HostHolder hostHolder;

    /**
     *
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // get certificate from cookie
        String ticket = CookieUtil.getValue(request, "ticket");
        if(ticket != null){
            // query the certificate
            LoginTicket loginTicket = userService.findLoginTicket(ticket);

            // check if the certificate valid
            if(loginTicket != null && loginTicket.getStatus() == 0 && loginTicket.getExpired().after(new Date())){
                // query users base on the certificate
                User user = userService.findUserById(loginTicket.getUserId());

                // hold this user during this request
                hostHolder.setUser(user);
            }
        }
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
        User user = hostHolder.getUser();
        if(user != null && modelAndView != null){
            modelAndView.addObject("loginUser", user);
        }
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        hostHolder.clear();
    }
}