Log incoming HTTP Request headers with a Server Filter

Learn to log every HTTP Request header with a @ServerFilter and a method annotated with @FilterRequest.

Authors: Sergio del Amo

Micronaut Version: 4.5.0

1. Getting Started

In this guide, we will create a Micronaut application written in Kotlin.

2. What you will need

To complete this guide, you will need the following:

3. Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

4. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
    --features= \
    --build=maven \
    --lang=kotlin \
If you don’t specify the --build argument, Gradle is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.
If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

If you use Micronaut Launch, select Micronaut Application as application type and add null features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

5. Logback

Configure Logback to log the package example.micronaut with TRACE level.

    <logger name="example.micronaut" level="TRACE"/>

6. ServerFilter

Create a filter which logs the non-sensitive HTTP Request headers.

package example.micronaut

import io.micronaut.core.order.Ordered
import io.micronaut.http.HttpRequest
import io.micronaut.http.annotation.Filter
import io.micronaut.http.annotation.RequestFilter
import io.micronaut.http.annotation.ServerFilter
import io.micronaut.http.filter.ServerFilterPhase
import io.micronaut.http.util.HttpHeadersUtil
import org.slf4j.Logger
import org.slf4j.LoggerFactory

@ServerFilter(Filter.MATCH_ALL_PATTERN) (1)
class LoggingHeadersFilter : Ordered {

    @RequestFilter (2)
    fun filterRequest(request: HttpRequest<*>) {
        HttpHeadersUtil.trace(LOG, request.headers)

    override fun getOrder() = ServerFilterPhase.FIRST.order() (3)

    companion object {
        private val LOG: Logger = LoggerFactory.getLogger(LoggingHeadersFilter::class.java)
1 @ServerFilter marks a bean as a filter for the HTTP Server. The annotation value Filter.MATCH_ALL_PATTERN means the filter matches all requests.
2 A filter method annotated with @RequestFilter runs before the request is processed. A filter method must be declared in a bean annotated with @ServerFilter or @ClientFilter.
3 Filters can be ordered by implementing Ordered in the filter class.

7. Controller

Create a controller which responds a JSON object: {"message":"Hello World"}.

package example.micronaut

import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get

@Controller (1)
class HelloController {

    @Get (2)
    fun index() = mapOf("message" to "Hello World") (3)
1 The class is defined as a controller with the @Controller annotation mapped to the path /.
2 The @Get annotation maps the method to an HTTP GET request.
3 The Micronaut framework will automatically convert it to JSON before sending it.

8. Running the Application

To run the application, use the ./mvnw mn:run command, which starts the application on port 8080.

curl localhost:8080 -H "X-Request-Id: 1234"

You will see in the logs:

... TRACE e.micronaut.LoggingHeadersFilter - Host: localhost:8080
... TRACE e.micronaut.LoggingHeadersFilter - User-Agent: curl/8.4.0
... TRACE e.micronaut.LoggingHeadersFilter - Accept: */*
... TRACE e.micronaut.LoggingHeadersFilter - X-Request-Id: 1234

9. Tests

10. Logback Dependency in test scope

In addition to the runtime classpath, add the logback-classic dependency to the test classpath:


10.1. Write tests

Create a MemoryAppender to ease testing.

package example.micronaut

import ch.qos.logback.classic.spi.ILoggingEvent
import ch.qos.logback.core.AppenderBase

class MemoryAppender : AppenderBase<ILoggingEvent>() {

    private val events = mutableListOf<ILoggingEvent>()

    override fun append(e: ILoggingEvent) {

    fun getEvents() = events

Create a test that verifies the filter logs HTTP header. It masks sensitive HTTP headers.

package example.micronaut

import ch.qos.logback.classic.Logger
import ch.qos.logback.classic.spi.ILoggingEvent
import io.micronaut.http.HttpHeaders
import io.micronaut.http.HttpRequest
import io.micronaut.http.client.HttpClient
import io.micronaut.http.client.annotation.Client
import io.micronaut.test.extensions.junit5.annotation.MicronautTest
import org.junit.jupiter.api.Assertions.assertDoesNotThrow
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import org.slf4j.LoggerFactory

@MicronautTest (1)
class HelloControllerTest {

    fun testHelloFilterLogging(@Client("/") httpClient: HttpClient) { (2)
        val appender = MemoryAppender()
        val l = LoggerFactory.getLogger(LoggingHeadersFilter::class.java) as Logger

        val client = httpClient.toBlocking()
        assertDoesNotThrow<String> {
                    .header(HttpHeaders.AUTHORIZATION, "Bearer x")
                    .header("foo", "bar")
            .map { obj: ILoggingEvent -> obj.formattedMessage }
            .anyMatch { it == "foo: bar" }

            .map { obj: ILoggingEvent -> obj.formattedMessage }
            .anyMatch { it == "Authorization: *MASKED*" }

            .map { obj: ILoggingEvent -> obj.formattedMessage }
            .noneMatch() { it == "Authorization: Bearer x" }

1 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. More info.
2 Inject the HttpClient bean and point it to the embedded server.

11. Testing the Application

To run the tests:

./mvnw test

12. Next steps

Explore more features with Micronaut Guides.

Learn more about Filter Methods.

13. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

14. License

All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…​).