Spring filter losing set variables after init function

Question

I'm having a weird problem with a simple spring filter I'm using. In the init function I'm setting a variable this.test = "TEST1234" but for some reason when reaching then doFilter function this variable is reverted to null again.

My filter:

@Component
public class TestFilter implements Filter {
    private String test;

    public void init(FilterConfig cfg) {
        this.test = "TEST1234";
        System.out.println("TEST: " + this.test);

    }

    public void doFilter(
        ServletRequest request,
        ServletResponse response,
        FilterChain chain) throws IOException, ServletException {
        System.out.println("TEST: " + this.test);
    }

    public void destroy() {}
}

SecurityConfig:

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .addFilterBefore(
                    new TestFilter(), 
                    AbstractPreAuthenticatedProcessingFilter.class
                );
    }
}

Console output:

init: TEST: TEST1234 doFilter: TEST: null

Why is this variable reverted to null? Am I missing something? Is it garbage collected?

I'm running my application on Java 1.8.0_171

Dependencies:

• Spring boot starter web: 2.1.4.RELEASE
• Spring security jwt: 1.0.10.RELEASE
• Spring security oauth2: 2.2.1.RELEASE
• Javax servlet: 2.5

Answer 1

Solved it thanks to the comment from @dur.

First I removed the @Component annotation so my filter doesn't get instantiated twice.

Filter:

public class TestFilter implements Filter {
    private String test;

    public void init(FilterConfig cfg) {
        this.test = "TEST1234";
        System.out.println("TEST: " + this.test);

    }

    public void doFilter(
        ServletRequest request,
        ServletResponse response,
        FilterChain chain) throws IOException, ServletException {
        System.out.println("TEST: " + this.test);
    }

    public void destroy() {}
}

Also I have created the filter instance as a bean instead of calling newFilter() directly in the addFilterBefore() function.

SecurityConfig:

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Bean
    public TestFilter testFilter() {
        return new TestFilter();
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .addFilterBefore(
                        testFilter(),
                        AbstractPreAuthenticatedProcessingFilter.class
                );
    }
}

Console output (now as expected):

init: TEST: TEST1234 doFilter: TEST: TEST1234