详解java中spring里的三大拦截器

Filter

新建 TimeFilter

@Component
public class TimeFilter implements Filter {
  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    System.out.println("time filter init");
  }

  @Override
  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    System.out.println("time filter start");
    long startTime = System.currentTimeMillis();

    filterChain.doFilter(servletRequest, servletResponse);

    long endTime = System.currentTimeMillis();
    System.out.println("time filter consume " + (endTime - startTime) + " ms");
    System.out.println("time filter end");
  }

  @Override
  public void destroy() {
    System.out.println("time filter init");
  }
}

启动服务器，在浏览器输入：http://localhost:8080/hello?name=tom

可以在控制台输出如下结果：

time filter start
name: tom
time filter consume 3 ms
time filter end

可以看到，filter 先执行，再到真正执行 HelloController.sayHello() 方法。
通过 TimeFilter.doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) 方法的参数可以看出，我们只能得到原始的 request 和 response对象，不能得到这个请求被哪个 Controller 以及哪个方法处理了，使用Interceptor 就可以获得这些信息。

Interceptor

新建 TimeInterceptor

@Component
public class TimeInterceptor extends HandlerInterceptorAdapter {

  private final NamedThreadLocal<Long> startTimeThreadLocal = new NamedThreadLocal<>("startTimeThreadLocal");

  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    System.out.println("time interceptor preHandle");

    HandlerMethod handlerMethod = (HandlerMethod) handler;
    // 获取处理当前请求的 handler 信息
    System.out.println("handler 类：" + handlerMethod.getBeanType().getName());
    System.out.println("handler 方法：" + handlerMethod.getMethod().getName());

    MethodParameter[] methodParameters = handlerMethod.getMethodParameters();
    for (MethodParameter methodParameter : methodParameters) {
      String parameterName = methodParameter.getParameterName();
      // 只能获取参数的名称，不能获取到参数的值
      //System.out.println("parameterName: " + parameterName);
    }

    // 把当前时间放入 threadLocal
    startTimeThreadLocal.set(System.currentTimeMillis());

    return true;
  }

  @Override
  public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    System.out.println("time interceptor postHandle");
  }

  @Override
  public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    // 从 threadLocal 取出刚才存入的 startTime
    Long startTime = startTimeThreadLocal.get();
    long endTime = System.currentTimeMillis();

    System.out.println("time interceptor consume " + (endTime - startTime) + " ms");

    System.out.println("time interceptor afterCompletion");
  }
}

注册 TimeInterceptor

把 TimeInterceptor 注入 spring 容器

@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

  @Autowired
  private TimeInterceptor timeInterceptor;

  @Override
  public void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(timeInterceptor);
  }
}

启动服务器，在浏览器输入：http://localhost:8080/hello?name=tom

可以在控制台输出如下结果：

time filter start
time interceptor preHandle
handler 类：com.nextyu.demo.web.controller.HelloController
handler 方法：sayHello
name: tom
time interceptor postHandle
time interceptor consume 40 ms
time interceptor afterCompletion
time filter consume 51 ms
time filter end

可以看到，filter 先于 interceptor 执行，再到真正执行 HelloController.sayHello() 方法。通过 interceptor 方法上的 handler 参数，我们就可以得到这个请求被哪个 Controller 以及哪个方法处理了。但是不能直接获取到这个方法上的参数值（在这里就是 HelloController.sayHello(String name) 方法参数 name 的值），通过 Aspect 就可以获取到。

Aspcet

新建 TimeAspect

@Aspect
@Component
public class TimeAspect {

  @Around("execution(* com.nextyu.demo.web.controller.*.*(..))")
  public Object handleControllerMethod(ProceedingJoinPoint pjp) throws Throwable {

    System.out.println("time aspect start");

    Object[] args = pjp.getArgs();
    for (Object arg : args) {
      System.out.println("arg is " + arg);
    }

    long startTime = System.currentTimeMillis();

    Object object = pjp.proceed();

    long endTime = System.currentTimeMillis();
    System.out.println("time aspect consume " + (endTime - startTime) + " ms");

    System.out.println("time aspect end");

    return object;
  }

}

启动服务器，在浏览器输入：http://localhost:8080/hello?name=tom

可以在控制台输出如下结果：

time filter start
time interceptor preHandle
handler 类：com.nextyu.demo.web.controller.HelloController
handler 方法：sayHello
time aspect start
arg is tom
name: tom
time aspect consume 0 ms
time aspect end
time interceptor postHandle
time interceptor consume 2 ms
time interceptor afterCompletion
time filter consume 4 ms
time filter end

可以看到，filter 先执行，再到 interceptor 执行，再到 aspect 执行，再到真正执行 HelloController.sayHello() 方法。
我们也获取到了 HelloController.sayHello(String name) 方法参数 name 的值。

请求拦截过程图

graph TD
httprequest-->filter
filter-->interceptor
interceptor-->aspect
aspect-->controller