实现方式

第一种方式

继承自 OncePerRequestFilter 并标记 @Component 组件

@Component
public class MyFilter extends OncePerRequestFilter {

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("Filter: MyFilter 执行之前");
        chain.doFilter(request, response);
        System.out.println("Filter: MyFilter 执行之后");
    }

}

第二种方式

@Configuration
public class FilterConfig {

    @Bean
    public FilterRegistrationBean filterRegistration() {
        FilterRegistrationBean registration = new FilterRegistrationBean();
        registration.setFilter(new OncePerRequestFilter() {
            @Override
            protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws ServletException, IOException {
                System.out.println("Filter: filterRegistration 执行 执行之前");
                chain.doFilter(request, response);
                System.out.println("Filter: filterRegistration 执行 执行之后");
            }
        });
        registration.addUrlPatterns("/*");
        registration.addInitParameter("paramName", "paramValue");
        registration.setName("filterRegistration");
        registration.setOrder(Integer.MIN_VALUE);
        return registration;
    }
}

这种方式可以对 Filter 做更详细的设置，如拦截的url、初始化参数、拦截器order

用途

拦截请求，可以对请求做「权限验证」，比如验证码校验。

github地址: https://github.com/jkxyx205/spring-boot-learn/tree/master/spring-mvc-filter