Filters vs. Interceptors in Java: Key Differences and Use Cases

Introduction

When developing Java web applications, understanding the difference between filters and interceptors is essential. Both serve as middleware components that help in request processing, but they have distinct roles and use cases. This article provides an in-depth comparison between filters and interceptors in Java, particularly in Spring Boot and Quarkus, to help developers make informed decisions when implementing them in their projects.

What Are Filters?

Filters in Java operate at the servlet level and allow developers to modify requests and responses before they reach servlets or after servlets generate responses. Filters are primarily used for:

• Authentication and Authorization
• Logging and Monitoring
• Compression and Encoding
• CORS Handling

Implementing Filters in Spring Boot

Spring Boot uses the javax.servlet.Filter interface to define filters. Here is an example:

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import java.io.IOException;

public class CustomFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("Request received at Filter");
        chain.doFilter(request, response);
        System.out.println("Response sent from Filter");
    }
}

Registering a Filter in Spring Boot

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FilterConfig {
    @Bean
    public FilterRegistrationBean<CustomFilter> loggingFilter() {
        FilterRegistrationBean<CustomFilter> registrationBean = new FilterRegistrationBean<>();
        registrationBean.setFilter(new CustomFilter());
        registrationBean.addUrlPatterns("/*");
        return registrationBean;
    }
}

What Are Interceptors?

Interceptors operate at the framework level, specifically in Spring MVC and Quarkus, and allow processing of HTTP requests before and after they reach controllers. Interceptors are used for:

• Pre-processing and Post-processing of Requests
• Performance Monitoring
• Request Modification
• Handling Cross-cutting Concerns

Implementing Interceptors in Spring Boot

Spring Boot uses the HandlerInterceptor interface for interceptors. Here’s an example:

import org.springframework.web.servlet.HandlerInterceptor;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CustomInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("Pre Handle method is Calling");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("Post Handle method is Calling");
    }
}

Registering an Interceptor in Spring Boot

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {
    @Autowired
    CustomInterceptor customInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(customInterceptor);
    }
}

Key Differences Between Filters and Interceptors

When to Use Filters and Interceptors?

Use Filters When:

• Working on low-level request/response modification.
• Applying security policies (e.g., authentication, authorization).
• Handling compression and encoding before processing.

Use Interceptors When:

• Pre-processing and post-processing request handling.
• Implementing cross-cutting concerns such as logging, validation, or auditing.
• Modifying business logic before reaching controllers.

FAQs

1. Can filters and interceptors be used together?

Yes, they can be used together. Filters handle servlet-level tasks, while interceptors handle business logic concerns.

2. Which executes first: a filter or an interceptor?

Filters execute before interceptors since they operate at the servlet level.

3. Can interceptors modify responses?

Yes, interceptors can modify responses in the postHandle() or afterCompletion() methods.

4. Are filters framework-dependent?

No, filters are part of the Java Servlet API, making them framework-independent.

5. Are interceptors limited to Spring Boot?

No, interceptors are also available in frameworks like Quarkus.

6. Can we register multiple filters and interceptors?

Yes, multiple filters and interceptors can be registered and executed in a specific order.

7. Do filters support dependency injection?

No, filters do not inherently support dependency injection. However, interceptors in Spring Boot support DI.

8. What is the best approach for implementing security: filters or interceptors?

Filters are better suited for authentication and authorization.

9. Can filters be applied to specific URLs?

Yes, filters can be mapped to specific URL patterns.

10. How can we disable an interceptor for specific URLs?

You can use excludePathPatterns() in InterceptorRegistry to disable interceptors for certain URLs.

External Links

• Spring Boot Official Documentation
• Servlet Filters in Java
• Interceptor in Spring Boot
• Quarkus Interceptor Guide

Conclusion

Understanding the difference between filters and interceptors is essential for Java professionals working with Spring Boot and Quarkus. Filters manage request and response modifications at the servlet level, whereas interceptors handle business logic concerns before reaching controllers. By knowing when and how to use these tools, developers can enhance application performance, security, and maintainability effectively.