Create filters in Spring Boot

This post will discuss how to create custom filters in a Spring Boot application that can apply to all URLs or only to certain URL patterns.

There are several ways to register a filter class in the Spring Boot application.

1. Implement the Filter interface

To create a custom filter, we can implement the Filter interface and annotate the filter with one of the Spring stereotypes, such as @Component for Spring to recognize it.

import org.springframework.core.annotation.Order;

import org.springframework.stereotype.Component;

import javax.servlet.*;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

@Component

public class MyFilter implements Filter {

@Override

public void doFilter(ServletRequest request,

ServletResponse response,

FilterChain chain) throws IOException, ServletException

{

HttpServletRequest req = (HttpServletRequest) request;

HttpServletResponse res = (HttpServletResponse) response;

System.out.println("Request URI is: " + req.getRequestURI());

chain.doFilter(request, response);

System.out.println("Response Status Code is: " + res.getStatus());

}

We can also extend the abstract class OncePerRequestFilter and annotate the filter with @Component. This is demonstrated below:

import org.springframework.stereotype.Component;

import org.springframework.web.filter.OncePerRequestFilter;

import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

@Component

public class MyFilter extends OncePerRequestFilter {

@Override

protected void doFilterInternal(HttpServletRequest httpServletRequest,

HttpServletResponse httpServletResponse,

FilterChain filterChain)

throws ServletException, IOException {

System.out.println("Request URI is: " + httpServletRequest.getRequestURI());

filterChain.doFilter(httpServletRequest, httpServletResponse);

System.out.println("Response Status Code is: " + httpServletResponse.getStatus());

}

2. Register a @Bean of type FilterRegistrationBean

The above filter applies to all requests. If we want our filter to only apply to certain URL patterns, we can remove the @Component annotation from our filter class definition and register a @Bean of type FilterRegistrationBean in Spring @Configuration.

For example, the following filter applies to URLs that match the /execute/* pattern.

import org.springframework.boot.web.servlet.FilterRegistrationBean;

import org.springframework.context.annotation.Bean;

import javax.servlet.*;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MyFilter implements Filter {

@Override

public void doFilter(ServletRequest request,

ServletResponse response,

FilterChain chain) throws IOException, ServletException

{

HttpServletRequest req = (HttpServletRequest) request;

HttpServletResponse res = (HttpServletResponse) response;

System.out.println("Request URI is: " + req.getRequestURI());

chain.doFilter(request, response);

System.out.println("Response Status Code is: " + res.getStatus());

}

@Bean

public FilterRegistrationBean<MyFilter> filter()

{

FilterRegistrationBean<MyFilter> bean = new FilterRegistrationBean<>();

bean.setFilter(new MyFilter());

bean.addUrlPatterns("/execute/*"); // or, use `setUrlPatterns()`

return bean;

}

3. Using Servlet’s @WebFilter annotation

We can also use Servlet annotation @WebFilter to declare a filter that accepts only certain URL patterns. Since @WebFilter is not a Spring’s annotation, we need to use @ServletComponentScan annotation to register it, which can be added along with @SpringBootApplication annotation in the Main class.

import javax.servlet.*;

import javax.servlet.annotation.WebFilter;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebFilter(urlPatterns = "/execute/*")

public class FirstFilter implements Filter {

@Override

public void doFilter(ServletRequest request,

ServletResponse response,

FilterChain chain) throws IOException, ServletException

{

HttpServletRequest req = (HttpServletRequest) request;

HttpServletResponse res = (HttpServletResponse) response;

System.out.println("Request URI is: " + req.getRequestURI());

chain.doFilter(request, response);

System.out.println("Response Status Code is: " + res.getStatus());

}

That’s all about creating filters in Spring Boot.

Create filters in Spring Boot

1. Implement the Filter interface

2. Register a @Bean of type FilterRegistrationBean

3. Using Servlet’s @WebFilter annotation

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