How to Define a Spring Boot Filter?
Last updated: December 30, 2021
1. Overview
In this quick tutorial, we’ll explore how to define custom filters and specify their invocation order with the help of Spring Boot.
Further reading:
Find the Registered Spring Security Filters
Learn how to find all the registered Spring Security filters in an application.
Configure a Spring Boot Web Application
Some of the more useful configs for a Spring Boot application.
2. Defining Filters and the Invocation Order
Let’s start by creating two filters:
- TransactionFilter – to start and commit transactions
- RequestResponseLoggingFilter – to log requests and responses
In order to create a filter, we simply need to implement the Filter interface:
@Component
@Order(1)
public class TransactionFilter implements Filter {
@Override
public void doFilter(
ServletRequest request,
ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
LOG.info(
"Starting a transaction for req : {}",
req.getRequestURI());
chain.doFilter(request, response);
LOG.info(
"Committing a transaction for req : {}",
req.getRequestURI());
}
// other methods
}
@Component
@Order(2)
public class RequestResponseLoggingFilter implements Filter {
@Override
public void doFilter(
ServletRequest request,
ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
LOG.info(
"Logging Request {} : {}", req.getMethod(),
req.getRequestURI());
chain.doFilter(request, response);
LOG.info(
"Logging Response :{}",
res.getContentType());
}
// other methods
}
In order for Spring to recognize a filter, we need to define it as a bean with the @Component annotation.
Moreover, to have the filters fire in the right order, we need to use the @Order annotation.
2.1. Filter With URL Pattern
In the example above, our filters are registered by default for all of the URLs in our application. However, we may sometimes want a filter to only apply to certain URL patterns.
In this case, we have to remove the @Component annotation from the filter class definition and register the filter using a FilterRegistrationBean:
@Bean
public FilterRegistrationBean<RequestResponseLoggingFilter> loggingFilter(){
FilterRegistrationBean<RequestResponseLoggingFilter> registrationBean
= new FilterRegistrationBean<>();
registrationBean.setFilter(new RequestResponseLoggingFilter());
registrationBean.addUrlPatterns("/users/*");
registrationBean.setOrder(2);
return registrationBean;
}Note, that in this case we need to explicitly set the order using a setOrder() method.
Now the filter will only apply for paths that match the /users/* pattern.
To set URL patterns for the filter, we can use the addUrlPatterns() or setUrlPatterns() methods.
3. A Quick Example
Now let’s create a simple endpoint and send an HTTP request to it:
@RestController
@RequestMapping("/users")
public class UserController {
@GetMapping()
public List<User> getAllUsers() {
// ...
}
}The application logs on hitting this API are :
23:54:38 INFO com.spring.demo.TransactionFilter - Starting Transaction for req :/users
23:54:38 INFO c.s.d.RequestResponseLoggingFilter - Logging Request GET : /users
...
23:54:38 INFO c.s.d.RequestResponseLoggingFilter - Logging Response :application/json;charset=UTF-8
23:54:38 INFO com.spring.demo.TransactionFilter - Committing Transaction for req :/usersThis confirms the filters are invoked in the desired order.
4. Conclusion
In this brief article, we summarized how to define custom filters in a Spring Boot webapp.
As always, the code snippets can be found over on GitHub.
