拦截器笔记

拦截器

Spring MVC中所有的拦截器都实现/继承自HandlerInterceptor接口。自定义拦截器，就需要实现/继承HandlerInterceptor接口或其子接口/实现类。下图为Spring MVC中拦截器的类图。

HandlerInterceptor接口的源码：

public interface HandlerInterceptor {

	//处理器执行前被调用
    default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return true;
    }
	//处理器执行后、视图渲染前被调用
    default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
    }
	//视图渲染完成后调用
    default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
    }
}

拦截器的执行流程：

新建一个LogInterceptor类并实现HandlerInterceptor接口：

public class LogInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        log.info("preHandle");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("postHandle");
    }

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

新建一个WebConfigurer类并实现WebMvcConfigurer接口，用于注册自定义的拦截器：

public class WebConfigurer implements WebMvcConfigurer {

    @Autowired
    private LogInterceptor logInterceptor;

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

在HelloController类的hello方法中添加一条日志打印代码：

public class HelloController {

    @GetMapping("/hello")
    public String hello() {
        log.info("hello");
        return "Hello Spring Boot";
    }

}

启动工程，访问http://localhost：8080/hello，会在控制台看到如下输出：

多个拦截器的执行顺序：

preHandle方法与afterCompletion方法总是成对出现的，一个拦截器的preHandle方法被调用后，afterCompletion方法必然也会被调用。
再创建一个拦截器，用来记录程序执行消耗的时间，并创建一个TimeInterceptor类，同样实现HandlerInterceptor接口，代码如下：

public class TimeInterceptor implements HandlerInterceptor {

    private final ThreadLocal<LocalTime> threadLocalStart = new ThreadLocal<>();
    private final ThreadLocal<LocalTime> threadLocalEnd = new ThreadLocal<>();
    private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm:ss:SSS");

    // 记录开始时间
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        LocalTime startTime = LocalTime.now();
        threadLocalStart.set(startTime);
        log.info("开始时间：{}", startTime.format(formatter));
        return true;
    }

    // 记录结束时间
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        LocalTime endTime = LocalTime.now();
        threadLocalEnd.set(endTime);
        log.info("结束时间：{}", endTime.format(formatter));
    }

    // 计算接口执行时间
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        LocalTime startTime = threadLocalStart.get();
        LocalTime endTime = threadLocalEnd.get();
        log.info("接口执行时间：{} 毫秒", Duration.between(startTime, endTime).getNano() / 1000000);
    }
}

然后将TimeInterceptor类配置到WebConfigurer类中，完成拦截器的注册。

@Configuration
public class WebConfigurer implements WebMvcConfigurer {

    @Autowired
    private LogInterceptor logInterceptor;
    @Autowired
    private TimeInterceptor timeInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(logInterceptor).addPathPatterns("/*");
        registry.addInterceptor(timeInterceptor);
    }
}

启动工程并再次访问hello接口，我们会看到控制台输出如下日志：