Interceptor拦截器

拦截器是基于 Java 反射机制实现的，因此拦截器只能拦截实现了接口的类，而不能拦截 url 这种链接。只能拦截部分 web 请求

在 Dispatcher 的 doDispatch方法中被调用。找到 Handler 和HandlerAdapter之后执行

Interceptor 中的方法执行顺序为 preHandle – Controller 方法 – postHandle – afterCompletion ，所以拦截器实际上可以对 Controller 方法执行前后进行拦截监控。

// 1. 先找 Handler
mappedHandler = this.getHandler(processedRequest);
// 2. 根据 Handler类型匹配 HandlerAdapter
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
// 3. 调用拦截器PreHandle
if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; }

// 4. 执行 Controller 层方法中的逻辑
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
// 5. 调用拦截器postHandle
mappedHandler.applyPostHandle(processedRequest, response, mv);


// 拦截器执行逻辑
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
    for(int i = 0; i < this.interceptorList.size(); this.interceptorIndex = i++) {
        HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i);
        if (!interceptor.preHandle(request, response, this.handler)) {
            this.triggerAfterCompletion(request, response, (Exception)null);
            return false;
        }
    }

    return true;
}

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv) throws Exception {
    for(int i = this.interceptorList.size() - 1; i >= 0; --i) {
        HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i);
        interceptor.postHandle(request, response, this.handler, mv);
    }

}

使用拦截器

创建拦截器

实现 HandlerInterceptor

public class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println(new Date() + "--preHandle:" + request.getRequestURL());
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println(new Date() + "--postHandle:" + request.getRequestURL());
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println(new Date() + "--afterCompletion:" + request.getRequestURL());
    }
}

配置拦截器

WebMvcConfigurer实现类中添加拦截器

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Resource
    private MyInterceptor myInterceptor;

    /**
     * 添加Web项目的拦截器
     */
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(myInterceptor).addPathPatterns("/**")
                .excludePathPatterns("/", "/login", "/index.html", "/user/login", "/css/**", "/images/**", "/js/**", "/fonts/**");
    }
}

拦截器的种类

MethodInterceptor

HandlerInterceptor