How to Inject Dependencies into a Servlet Filter with Spring Boot Filter Registration Bean?

Question

I have a Servlet Filter within my Spring Boot (2.0.1) application that I'm registering with FilterRegistrationBean which I need it to be executed first (order of one) along the filter chain. The application is deployed to JBoss 7.2 . This filter also has a dependency that is injected with @Autowired (see below):

package my.pkg.com
@SpringBootApplication
@ComponentScan(basePackages={"my.pkg.com"})
public class MyApp extends SpringBootServletInitializer {
  public satic void main(String[] args) throws IOException {
    SpringApplication.run(MyApp.class, args);
  }

  @Bean
  @Order(1)
  public FilterRegistrationBean<MyFilter> myFilter() {
    FilterRegistrationBean<MyFilter> contextFilter = new FilterRegistrationBean<>();
    contextFilter.setFilter(new MyFilter());
    contextFilter.addUrlPattern("/api/*");
    return contextFilter;
  }
}


package my.pkg.com.filter

public class MyFilter extends Filter {

  @Autowired
  private MyService mySrv;


  @Override

  public void doFilter(…) {

    mySrv.doSomething(); // mySrv is null
  }
}

The problem is when the application is deployed and ran, when the Servlet request gets to MyFilter.doFilter() , mySrv is null which means MyFilter was never scanned for dependency injections.

I can verify through debugging MyService which is a @Repository in my.package.com.repository package does get initialized. It just never gets injected into MyFilter .

I can create a constructor for MyFilter to take MyService , then @Autowired MyService into MyApp and during filter registration, I can pass it to this constructor, which resolves the issue.

However, I want to know if there is anything I'm doing wrong that this dependency doesn't get injected into MyFilter with using the setup above alone.

Answer 1

If you create an object by yourself, using new , and this object is not returned by a @Bean -annotated method, then it's not a Spring bean, and Spring will thus not inject anything in it.

You can just add an @Bean-annotated method returning new MyFilter() , and call that method from myFilter() to get the bean, or add a MyFilter as argument to myFilter() .

Example:

@Bean
@Order(1)
public FilterRegistrationBean<MyFilter> myFilter() {
    FilterRegistrationBean<MyFilter> contextFilter = new FilterRegistrationBean<>();
    contextFilter.setFilter(theActualFilter());
    contextFilter.addUrlPattern("/api/*");
    return contextFilter;
}

@Bean 
public MyFilter theActualFilter() {
    return new MyFilter(); // now this is a Spring bean
}

or

@Bean
@Order(1)
public FilterRegistrationBean<MyFilter> myFilter(MyFilter theActualFilter) {
    FilterRegistrationBean<MyFilter> contextFilter = new FilterRegistrationBean<>();
    contextFilter.setFilter(theActualFilter);
    contextFilter.addUrlPattern("/api/*");
    return contextFilter;
}

@Bean 
public MyFilter theActualFilter() {
    return new MyFilter(); // now this is a Spring bean
}

Answer 2

很简单，在过滤器类上添加@Component批注，它将使@Autowired批注在内部起作用，因为Spring依赖项注入将处理您的过滤器类并注入服务bean。