spring security自定义filter重复执行

引自

@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Bean
    public DemoFilter demoFilter(){
        return new DemoFilter();
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.addFilterBefore(demoFilter(),AnonymousAuthenticationFilter.class).
        authorizeRequests().
        antMatchers("/login","/css/**", "/js/**","/fonts/**").
        permitAll().
        anyRequest().
        authenticated();
    }
}

public class DemoFilter extends GenericFilterBean {

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //do something
        filterChain.doFilter(servletRequest, servletResponse);
    }
}

原因

在spring容器托管的GenericFilterBean的bean，都会自动加入到servlet的filter chain，而上面的定义，还额外把filter加入到了spring security的
AnonymousAuthenticationFilter之前。而spring security也是一系列的filter，在mvc的filter之前执行。因此在鉴权通过的情况下，就会先后各执行一次。

解决方案

方案1
不把filter托管给spring，直接new，比如

@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .addFilterBefore(new DemoFilter(),AnonymousAuthenticationFilter.class)
                .authorizeRequests()
                .antMatchers("/login","/css/**", "/js/**","/fonts/**").permitAll()
                .anyRequest().authenticated();
    }
}

方案2
有时候filter需要访问spring容器的资源，托管给容器可能好些，那么这个时候，就可以像FilterSecurityInterceptor做个标记FILTER_APPLIED

public class DemoFilter extends GenericFilterBean {

    private static final String FILTER_APPLIED = "__spring_security_demoFilter_filterApplied";

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        if (servletRequest.getAttribute(FILTER_APPLIED) != null) {
            filterChain.doFilter(servletRequest, servletResponse);
            return ;
        }
        //do something
        servletRequest.setAttribute(FILTER_APPLIED,true);
        filterChain.doFilter(servletRequest, servletResponse);
    }
}