Notice
I wrote this article and was originally published on Qiita on 4 September 2021.
What is servlet filter
You can get the answer from here.
How Spring Boot creates and loads filter
First creates bean which implements javax.servlet.Filter interface (Normally filter bean is extended from org.springframework.web.filter.GenericFilterBean class). Below is an example
public class HttpEncodingAutoConfiguration {
//...
@Bean
@ConditionalOnMissingBean
public CharacterEncodingFilter characterEncodingFilter() {
CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
filter.setEncoding(this.properties.getCharset().name());
filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
return filter;
}
// ...
}
Then during Servlet registrate to servlet container (Servlet class is org.springframework.web.servlet.DispatcherServlet), beans created above will be collected and registered at
public class ServletContextInitializerBeans extends AbstractCollection<ServletContextInitializer> {
// ...
@SuppressWarnings("unchecked")
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
// *** HERE ***
addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
new ServletListenerRegistrationBeanAdapter());
}
}
// ...
}
Filter registered by default
| Filter | Function |
|---|---|
| org.springframework.security.web.FilterChainProxy | Used by Spring Security. It holds many sub-filter for performing security policy |
| org.springframework.boot.web.servlet.filter.OrderedRequestContextFilter | Exposes the request object to the current thread |
| org.springframework.boot.web.servlet.filter.OrderedHiddenHttpMethodFilter | Converts posted method parameters into HTTP methods |
| org.springframework.boot.web.servlet.filter.OrderedFormContentFilter | Parses form data for HTTP PUT, PATCH, and DELETE requests and exposes it as Servlet request parameters. By default the Servlet spec only requires this for HTTP POST |
| org.springframework.boot.web.servlet.filter.OrderedCharacterEncodingFilter | apply default character encoding for request if not specify in request |
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