What are the three major interceptors in spring in java learning?

The content of this article is to introduce what are the three major interceptors in spring. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Filter

New 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");
    }
}

Start the server and enter in the browser: http://localhost:8080/ hello?name=tom

can output the following results on the console:

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

You can see that the filter is executed first, and then the HelloController.sayHello() method is actually executed.
As can be seen from the parameters of the TimeFilter.doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) method, we can only get the original request and response objects, but cannot get which Controller and which controller the request was sent to. After the method is processed, this information can be obtained using Interceptor.

Interceptor

New 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");
    }
}</long>

Register TimeInterceptor
Inject TimeInterceptor into spring container

@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

    @Autowired
    private TimeInterceptor timeInterceptor;

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

Start the server and enter in the browser: http://localhost:8080/hello?name=tom
The following results can be output on the console:

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

As you can see, the filter is executed before the interceptor. Then actually execute the HelloController.sayHello() method. Through the handler parameter on the interceptor method, we can get which Controller and which method the request was processed by. However, the parameter value of this method cannot be obtained directly (here it is the value of the HelloController.sayHello(String name) method parameter name). It can be obtained through Aspect.

Aspcet

New 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;
    }

}

Start the server and enter in the browser: http://localhost:8080/ hello?name=tom
The following results can be output on the console:

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

As you can see, the filter is executed first, then the interceptor is executed, then the aspect is executed, and then HelloController.sayHello() is actually executed. method.
We also obtained the value of the HelloController.sayHello(String name) method parameter name.

Request interception process diagram

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

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