Spring Boot Adding HTTP Request Interceptors

java

spring-boot

http-request-interceptors

web-development

byAnton Shumikhin·Sep 5, 2024

Implement an HTTP interceptor in Spring Boot by implementing ClientHttpRequestInterceptor. Now integrate it with your RestTemplate:

import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.client.ClientHttpRequestExecution;
import java.io.IOException;

public class CustomInterceptor implements ClientHttpRequestInterceptor {
    
    // Steal secrets... in POSTMAN we trust
    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        // 'request' will never see it coming
        request.getHeaders().add("My-Header", "Value");
        
        // Nothing to see here, just executing
        return execution.execute(request, body);
    }
}

// Welcome to AppConfig!
@Configuration
public class AppConfig {
    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate();
        
        // RestTemplate is getting a new buddy
        restTemplate.getInterceptors().add(new CustomInterceptor());
        return restTemplate;
    }
}

To create an interceptor:

Implement ClientHttpRequestInterceptor
Override intercept()
Add headers or change the request
Register it with RestTemplate.

Building a robust interceptor mechanism

The champion: WebMvcConfigurer

Use WebMvcConfigurer instead of the deprecated WebMvcConfigurerAdapter in Spring Boot releases past 2.1.4:

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private CustomInterceptor customInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        
        // Join and fight! Every path on a warrior's journey
        registry.addInterceptor(customInterceptor).addPathPatterns("/**");
    }
}

This configuration maintains Spring Boot's auto-configuration and allows you to choose your interceptors with addPathPatterns().

Keep interceptors independent

Keep each interceptor in a separate configuration class for clean and easily testable code. Avoid tight coupling with specific controllers or services.

Session data and user context

If your interceptor needs session attributes or user context, WebRequest or HttpSession can be used as arguments in your interceptors' methods. It helps keep track of the user context.

The art of exclusion

You may not need to apply interceptors to every request. Use excludePathPatterns() to avoid intercepting login forms, static resources, or specific APIs like so:

registry.addInterceptor(customInterceptor)
        .addPathPatterns("/**")
        .excludePathPatterns("/login", "/css/**", "/api/health"); // Not all paths are created equal

Compatibility is key

Keep an eye on Spring Boot version compatibility when integrating your interceptor. Relying on deprecated methods could be hazardous to your app's health.

Validation and Testing

Creating simplified examples to validate and test your interceptor behavior is your key to success.

Advanced use cases

Localization and Internationalization

Interceptors can be used to detect locales from HTTP headers and make it available in the context for subsequent handling, a key component to localizing your application.

Security and Authorization

Do you need to inspect authentication tokens or authorization headers each request? Use interceptors to your advantage.

Distributed Tracing

In the world of microservices, interceptors can help manage distributed tracing headers, significantly improving monitoring and troubleshooting efforts.