13. Interceptor

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[Shang Silicon Valley] SpringBoot2 Zero-Basic Introductory Tutorial - Lecturer: Lei Fengyang
Notes

The road is still going on, the dream is still waiting

1. HandlerInterceptor interface

The underlying interface of the interceptor

Location: org.springframework.web.servlet.HandlerInterceptor

public interface HandlerInterceptor {
    
    

	default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
    
    

		return true;
	}

	default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
			@Nullable ModelAndView modelAndView) throws Exception {
    
    
	}

	default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
			@Nullable Exception ex) throws Exception {
    
    
	}
}

2. Interceptor use

2.1, custom interceptor

Writing an interceptor must implement the HandlerInterceptor interface

@Slf4j
public class LoginInterceptor implements HandlerInterceptor {
    
    

    // 目标方法执行之前
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    
    

        String requestURI = request.getRequestURI();
        log.info("preHandle拦截的请求路径是{}",requestURI);
        //登录检查逻辑
        HttpSession session = request.getSession();
        Object loginUser = session.getAttribute("loginUser");
        if(loginUser != null){
    
    
            //放行
            return true;
        }
        //拦截住，未登录，跳转到登录页
        request.setAttribute("msg","请先登录");
        //re.sendRedirect("/");
        request.getRequestDispatcher("/").forward(request,response);
        return false;
    }

    // 目标方法执行完成以后
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    
    
        log.info("postHandle执行{}",modelAndView);
    }

    // 页面渲染以后
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    
    
        log.info("afterCompletion执行异常{}",ex);
    }
}

2.2, configure the interceptor

The interceptor is registered in the container (implements the addInterceptors method of the WebMvcConfigurer interface)

Specify interception rules [if all are intercepted, static resources will also be intercepted]

@Configuration
public class AdminWebConfig implements WebMvcConfigurer {
    
    

    // 向容器中添加自定义拦截器
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
    
    
        // 在拦截器注册中心中添加 LoginInterceptor 拦截器
        registry.addInterceptor(new LoginInterceptor())
                // 拦截的路径（所有请求都被拦截包括静态资源）
                .addPathPatterns("/**")
                // 放行的路径
                .excludePathPatterns("/","/login","/css/**","/fonts/**","/images/**","/js/**");
    }
}

3. Interceptor principle

• 1. According to the current request, find the HandlerExecutionChain . [Handlers that can handle requests and all interceptors of handlers]

• 2. Execute the preHandle methods of all interceptors in sequence first.
  • 1. If the current interceptor prehandler returns true, execute the preHandle of the next interceptor.
  • 2. If the current interceptor returns false, it will directly trigger the afterCompletion of all executed interceptors in reverse order.
• 3. If any interceptor fails to execute, return false, and jump out directly without executing the target method.
• 4. All interceptors return True and execute the target method.
• 5. Execute the postHandle methods of all interceptors in reverse order.
• 6. Any abnormality in the previous steps will directly trigger afterCompletion in reverse order.
• 7. After the page is successfully rendered, afterCompletion will also be triggered in reverse order.