Structured logging support by lujop · Pull Request #10746 · dropwizard/dropwizard

lujop · 2025-11-02T22:41:25Z

Add support for SLF4J 2.0 structured logging key-value pairs in EventJsonLayout. This allows developers to add structured data to individual log entries using the addKeyValue() API.

Problem:

Solves issue #9734
Support for SLF4J 2.0 structured logging in JSON Layout.

Solution:

Implement keyValuePairs handling into EventJsonLayout in the same way MDC values are handled.
By default all pairs are logged in nested format but they can be filtered and flattened using configuration parameters.

KEY_VALUE_PAIRS has been added to EventAttribute enum to be able to disable it.

Result:

Given

 logger.atInfo()
        .addKeyValue("userId", userId)
        .addKeyValue("action", "login")
        .addKeyValue("duration", duration)
        .log("User login completed");

by default is rendered into:

  {
    "timestamp": "2024-01-02T15:19:21.000+0000",
    "level": "INFO",
    "message": "User login completed",
    "keyValuePairs": {
      "userId": "12345",
      "action": "login",
      "duration": 150
    }
  }

Add support for SLF4J 2.0 structured logging key-value pairs in EventJsonLayout. This allows developers to add structured data to individual log entries using the addKeyValue() API. Closes dropwizard#9734

lujop · 2025-11-05T20:33:30Z

I left it in draft because I forgot to ask my employer for permission, but I'm currently in the process of getting it.

lujop · 2026-01-18T17:23:51Z

Put it again on review. I got the approval, but I didn't do it at the moment and forgot for some time 🙈

Copilot

Pull request overview

This pull request adds support for SLF4J 2.0 structured logging key-value pairs in the JSON logging layout. The implementation follows the existing MDC pattern, allowing developers to add structured data to log entries using the addKeyValue() API. By default, key-value pairs are logged in nested format under the keyValuePairs field, but can be filtered and flattened using new configuration parameters.

Changes:

Added KEY_VALUE_PAIRS to the EventAttribute enum to allow enabling/disabling this feature
Implemented key-value pair handling in EventJsonLayout with filtering and flattening support
Added configuration properties includesKeyValuePairsKeys and flattenKeyValuePairs to EventJsonLayoutBaseFactory
Enhanced MapBuilder to handle Boolean values and generic Objects with type-aware serialization
Added comprehensive test coverage for all new functionality
Documented the structured logging feature and configuration options

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/EventAttribute.java	Added KEY_VALUE_PAIRS enum value to support the new attribute
dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/layout/EventJsonLayout.java	Core implementation: added logic to process, filter, and flatten key-value pairs similar to MDC handling
dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/EventJsonLayoutBaseFactory.java	Added configuration properties for key-value pairs (includesKeyValuePairsKeys, flattenKeyValuePairs) and included KEY_VALUE_PAIRS in default attributes
dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/layout/MapBuilder.java	Added addBoolean and generic add methods to support proper type serialization of key-value pair values
dropwizard-json-logging/src/test/java/io/dropwizard/logging/json/layout/EventJsonLayoutTest.java	Comprehensive test coverage for nested/flattened formats, filtering, null handling, and type conversion
dropwizard-json-logging/src/test/java/io/dropwizard/logging/json/LayoutIntegrationTests.java	Integration tests verifying configuration deserialization and end-to-end logging with key-value pairs
dropwizard-json-logging/src/test/resources/yaml/json-log.yml	Test configuration demonstrating key-value pairs configuration options
docs/source/manual/core.rst	Added "Structured Logging with JSON" section with usage examples and output format examples
docs/source/manual/configuration.rst	Updated JSON layout configuration documentation with new key-value pairs settings

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Copilot · 2026-01-25T22:37:49Z

...wizard-json-logging/src/test/java/io/dropwizard/logging/json/layout/EventJsonLayoutTest.java

+
+    @Test
+    void testLogsFlattenedKeyValuePairsFilteringNullValues() {
+        when(event.getKeyValuePairs()).thenReturn(List.of(new KeyValuePair("test", "value"),new KeyValuePair("testNull", null)));


Missing space after comma between the two KeyValuePair arguments. Should be: new KeyValuePair("test", "value"), new KeyValuePair("testNull", null)

Copilot · 2026-01-25T22:37:49Z

...wizard-json-logging/src/test/java/io/dropwizard/logging/json/layout/EventJsonLayoutTest.java

+    void testFilterKeyValueKeys() {
+        final Set<String> includesKeyValuePairsKeys = Set.of("test");
+        when(event.getKeyValuePairs()).thenReturn(List.of(new KeyValuePair("test", "value"), new KeyValuePair("test2", "value2")));
+        eventJsonLayout= new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, DEFAULT_EVENT_ATTRIBUTES,


Missing space before the assignment operator. Should be: eventJsonLayout = instead of eventJsonLayout=

Suggested change

eventJsonLayout= new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, DEFAULT_EVENT_ATTRIBUTES,

eventJsonLayout = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, DEFAULT_EVENT_ATTRIBUTES,

Copilot · 2026-01-25T22:37:49Z

...wizard-json-logging/src/test/java/io/dropwizard/logging/json/layout/EventJsonLayoutTest.java

+    @Test
+    void testFilterAndFlattenKeyValueKeys() {
+        final Set<String> includesKeyValuePairsKeys = Set.of("test");
+        when(event.getKeyValuePairs()).thenReturn(java.util.List.of(new KeyValuePair("test", "value"), new KeyValuePair("test2", "value2")));


Use List.of consistently instead of the fully qualified java.util.List.of. All other test methods in this file use the shorter form List.of.

Suggested change

when(event.getKeyValuePairs()).thenReturn(java.util.List.of(new KeyValuePair("test", "value"), new KeyValuePair("test2", "value2")));

when(event.getKeyValuePairs()).thenReturn(List.of(new KeyValuePair("test", "value"), new KeyValuePair("test2", "value2")));

Copilot · 2026-01-25T22:37:50Z

dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/layout/EventJsonLayout.java

        }

+        final boolean includeKeyValuePairs = isIncluded(EventAttribute.KEY_VALUE_PAIRS);
+        if(includeKeyValuePairs && event.getKeyValuePairs() != null) {


Missing space after if keyword. Should be: if (includeKeyValuePairs instead of if(includeKeyValuePairs

Suggested change

if(includeKeyValuePairs && event.getKeyValuePairs() != null) {

if (includeKeyValuePairs && event.getKeyValuePairs() != null) {

Copilot · 2026-01-25T22:37:50Z

dropwizard-json-logging/src/test/java/io/dropwizard/logging/json/LayoutIntegrationTests.java

 import io.dropwizard.logging.common.DefaultLoggingFactory;
 import io.dropwizard.request.logging.LogbackAccessRequestLogFactory;
 import io.dropwizard.validation.BaseValidator;
+import jdk.jfr.Event;


The import jdk.jfr.Event is unused and should be removed.

Suggested change

import jdk.jfr.Event;

Copilot · 2026-01-25T22:37:50Z

...wizard-json-logging/src/test/java/io/dropwizard/logging/json/layout/EventJsonLayoutTest.java

+
+    @Test
+    void testLogsKeyValuePairsFilteringNullValues() {
+        when(event.getKeyValuePairs()).thenReturn(List.of(new KeyValuePair("test", "value"),new KeyValuePair("testNull", null)));


Missing space after comma between the two KeyValuePair arguments. Should be: new KeyValuePair("test", "value"), new KeyValuePair("testNull", null)

Copilot · 2026-01-25T22:37:50Z

dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/layout/MapBuilder.java

+     * Adds the value to the provided map under the provided field name if it should be included.
+     * If the value is a String, Number, or Boolean it's added as it is, otherwise it's converted to string using `toString()`.
+     */
+    public MapBuilder add(String fieldName, boolean include, @Nullable Object value) {


Method MapBuilder.add(..) could be confused with overloaded method add, since dispatch depends on static types.
Method MapBuilder.add(..) could be confused with overloaded method add, since dispatch depends on static types.
Method MapBuilder.add(..) could be confused with overloaded method add, since dispatch depends on static types.

dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/layout/MapBuilder.java

+     * Adds the value to the provided map under the provided field name if it should be included.
+     * If the value is a String, Number, or Boolean it's added as it is, otherwise it's converted to string using `toString()`.
+     */
+    public MapBuilder add(String fieldName, boolean include, @Nullable Object value) {


Structured logging support

bac75cb

Add support for SLF4J 2.0 structured logging key-value pairs in EventJsonLayout. This allows developers to add structured data to individual log entries using the addKeyValue() API. Closes dropwizard#9734

lujop requested a review from a team as a code owner November 2, 2025 22:41

github-actions bot added this to the 5.0.1 milestone Nov 2, 2025

Don't create temporary list when filtering values

2784f28

lujop marked this pull request as draft November 5, 2025 20:27

lujop marked this pull request as ready for review January 18, 2026 17:22

Merge branch 'release/5.0.x' into feature/structured-logging-json-layout

2bfa577

joschi requested a review from Copilot January 25, 2026 22:32

Copilot started reviewing on behalf of joschi January 25, 2026 22:32 View session

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joschi modified the milestones: 5.0.1, 5.0.2 Jan 27, 2026

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Structured logging support#10746

Structured logging support#10746
lujop wants to merge 3 commits intodropwizard:release/5.0.xfrom
lujop:feature/structured-logging-json-layout

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	eventJsonLayout= new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, DEFAULT_EVENT_ATTRIBUTES,
	eventJsonLayout = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, DEFAULT_EVENT_ATTRIBUTES,

	when(event.getKeyValuePairs()).thenReturn(java.util.List.of(new KeyValuePair("test", "value"), new KeyValuePair("test2", "value2")));
	when(event.getKeyValuePairs()).thenReturn(List.of(new KeyValuePair("test", "value"), new KeyValuePair("test2", "value2")));

	if(includeKeyValuePairs && event.getKeyValuePairs() != null) {
	if (includeKeyValuePairs && event.getKeyValuePairs() != null) {

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lujop commented Nov 2, 2025

Problem:

Solution:

Result:

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