Why is My Spring Filter Being Invoked Twice, and How Can I Fix It?

Filter Registered Twice with Spring Bean Annotation

When registering a filter as a Spring bean, it is important to consider the potential for multiple invocations. In certain scenarios, the filter may be triggered twice, as observed in the following issue:

Issue:

A user defines a filter, A, which extends Spring's GenericFilterBean. When this filter is registered as a bean in the Spring Security configuration, an additional invocation is observed, resulting in the following output:

filter A before
filter A before
mycontroller invoke
filter A after
filter A after

Query:

Why is the filter being called twice, and how can this issue be resolved?

Answer:

The extra invocation occurs because Spring Boot automatically registers any bean of type Filter with the servlet container. To prevent this, there are two options:

Option 1: Register Filter with Spring Security Only

Avoid exposing the filter as a bean and register it solely with Spring Security, as follows:

@Override
protected void configure(HttpSecurity http) throws Exception {
    http.sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS);
    http.addFilterBefore(new A(), BasicAuthenticationFilter.class);
    http.csrf().disable();
}

Option 2: Use FilterRegistrationBean with Annotation

If autowiring dependencies into the filter is necessary, one can register it as a bean but disable its automatic registration with the servlet container using a FilterRegistrationBean:

@Bean
public FilterRegistrationBean registration(MyFilter filter) {
    FilterRegistrationBean<MyFilter> registration = new FilterRegistrationBean<MyFilter>(filter);
    registration.setEnabled(false);
    return registration;
}

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