Introduction to the implementation methods of filters and interceptors in springboot (code)

This article brings you an introduction to the implementation methods (code) of filters and interceptors in springboot. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Filters and interceptors are both manifestations of AOP programming ideas and can implement such things as permission checking, logging, etc. There are certain similarities between the two, but the difference is:

• Filter is a servlet specification and can only be used in Web programs, while interceptor is a Spring specification and can be used in Web programs program, and can also be used in the Application program.

• Filter is defined in servlet and depends on the servlet container. The interceptor is defined in Spring and depends on the Spring container.

• The interceptor is a Spring component, managed by Spring, and configured in the Spring configuration file, so it can use any Spring resource. For example, Services, data sources, etc. can be injected into the interceptor through the IOC container, but Filter cannot.

• Filter only works before and after the servlet, while the interceptor can go deep before and after the method, before and after the exception is thrown. Use more depth.

Implementing the filter Filter in Spring

Method 1: Use the FilterRegistrationBean provided by springboot to register a custom filter

public class MyFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("MyFilter init...");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //站点图标/favicon.ico  filter会执行2次
        HttpServletRequest request=(HttpServletRequest) servletRequest;
        System.out.println(request.getRequestURI());
        System.out.println("MyFilter dofilter...");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {

    }
}

Register Filter in springboot

@Configuration
public class FilterConfig {

    @Bean
    public FilterRegistrationBean registrationBean(){
        FilterRegistrationBean myfilter=new FilterRegistrationBean(new MyFilter());
        myfilter.addUrlPatterns("/*");

        return myfilter;
    }

When you run the demo here, you will find that do filter is executed twice. Debug found that this is because of browsing The site icon is managed when requested by the server and can be found through the uri. You can use regular expressions to control it appropriately according to your own needs.

Method 2: servlet annotation definition Filter

@Component
@WebFilter(filterName = "myFilter2",urlPatterns = "/*")
public class MyFilter2 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("myFilter2 init...");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("myFilter2 dofilter ...");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {

    }
}

The filter declared using the servleta annotation has only one request during execution. This is different from using spring configuration filter.

Implementing interceptors in Spring

Interceptors mainly use custom classes to integrate HandlerInterceptor. The program will continue to execute when preHandle returns true, and the request will be interrupted if it returns false.

public class MyInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("/preHandler");
        return true;
    }

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

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

Configure the interceptor in the program and declare the interception rules

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {

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

operation result

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