This article will talk about interceptors. It is convenient to register interceptors in springboot. There are about two steps:

1. Implement HandlerInterceptor interface to create interceptor

2. Implementation of WebMvcConfigurer interface configuration interceptor

Let's use a simple example to roughly show the following specific use:

Scenario: two pages, the login page can be accessed at will, but the home page can only be accessed by xiongda user after entering the correct password

The first step is to create an interceptor

public class MyInterceptor implements HandlerInterceptor{

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        System.out.println("==========jin  ru pre  handle ====");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        
        System.out.println(username +","+password);
        
        if("xiongda".equals(username) && "123456".equals(password)) {
            return true;
        }else {
            return false;
        }
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        System.out.println("================= jin ru  after ===============");
    }

}

Second, configure the interceptor

@Configuration
public class WebMvcConfig  implements WebMvcConfigurer{

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new MyInterceptor())
            .addPathPatterns("/**")
            .excludePathPatterns("/static/login.html");
    }
    
    
}

Next, we will explain according to the specific results:

The above two figures are to access the login page. The login page is configured with the exclusion path in the interceptor configuration. You can see that even if it is released, it will enter the prehandle, but no operation will be performed.

When entering the home page, the judgment will be made in the prehandle. Only when it is true will the subsequent afterCompletion method be executed.

Note:
1. The execution order of methods in the interceptor is prehandle - > controller - > posthandle - > aftercompletion.
Only when preHandle returns true will the following methods be executed