Spring Boot 3.4で追加された構造化ログ出力を試してみる

これは、なにをしたくて書いたもの？

Spring Boot 3.4から構造化ログを出力できるようになっているようなので、試しておこうかなということで。

Structured logging in Spring Boot 3.4

Spring Bootの構造化ログ

Structured Logging（構造化ログ）というのは、いわゆるJSONフォーマットでログを出力することです。

ドキュメントはこちら。

Logging / Structured Logging

Spring Boot 3.4での機能紹介ブログはこちら。

Structured logging in Spring Boot 3.4

構造化ログ自体は新しい話題ではありませんが、Spring Boot 3.4以前だと構造化ログを扱おうとすると他のライブラリーを追加する必要が
ありました。

以下あたりですね。

GitHub - logfellow/logstash-logback-encoder: Logback JSON encoder and appenders

ECS Logging Java | ECS Logging Java

ECSと聞くとAWSのサービスを連想するかもしれませんが、これはElastic Common SchemaのことでElasticsearchにログデータを取り込む際の
標準フォーマットのことです。

Elastic Common Schema (ECS) defines a common set of fields for ingesting data into Elasticsearch. For more information about ECS

ECS logging libraries | ECS logging libraries

Spring Bootに話を戻しましょう。

JSONフォーマットといってもいくつか種類があり、Spring Boot 3.5では次の3種類のフォーマットをサポートしています。

• Logging / Structured Logging / Elastic Common Schema
• Logging / Structured Logging / Graylog Extended Log Format (GELF)
• Logging / Structured Logging / Logstash JSON format

よく見るとECSやLogstashフォーマットがあり、これまでサードパーティー製のライブラリーを使っていたところをSpring Boot自身が
提供するようになった、と見ることができます。

いずれのフォーマットでもMDCに追加した内容はログに含まれるようです。またSLF4JのFluent Logging APIを使うことでキーと値を
追加することもできます。

Logstashフォーマットに限っては、SLF4JのMarkerを使うことでtagsにできるようです。

使い方としては、プロパティーを指定することでログの出力フォーマットがJSONに切り替わります。

# ECS
logging.structured.format.console=ecs
logging.structured.format.file=ecs


# Graylog
logging.structured.format.console=gelf
logging.structured.format.file=gelf

# Logstash
logging.structured.format.console=logstash
logging.structured.format.file=logstash

ECSについては標準のフィールドをカスタマイズできるようです。

logging.structured.ecs.service.name=MyService
logging.structured.ecs.service.version=1
logging.structured.ecs.service.environment=Production
logging.structured.ecs.service.node-name=Primary

その他、プロパティーでカスタマイズができたり

• logging.structured.json.include、logging.structured.json.exclude … 特定のパスのフィールドをフィルタリグ
• logging.structured.json.rename … 特定のフィールドをリネーム
• logging.structured.json.add … 特定のフィールドを追加

logging.structured.json.exclude=log.level
logging.structured.json.rename.process.id=procid
logging.structured.json.add.corpname=mycorp

Logging / Structured Logging / Customizing Structured Logging JSON

スタックトレースのカスタマイズができます。

Logging / Structured Logging / Customizing Structured Logging Stack Traces

それでも足りない場合は、自分でStructuredLogFormatterインターフェースを実装してフォーマットを作成するようです。

Logging / Structured Logging / Supporting Other Structured Logging Formats

Spring Bootの構造化ログに関するプロパティーはこちら。

Common Application Properties / Core Properties / logging.structured

ドキュメントを見るのはこれくらいにして、使ってみましょう。

環境

今回の環境はこちら。

$ java --version
openjdk 21.0.8 2025-07-15
OpenJDK Runtime Environment (build 21.0.8+9-Ubuntu-0ubuntu124.04.1)
OpenJDK 64-Bit Server VM (build 21.0.8+9-Ubuntu-0ubuntu124.04.1, mixed mode, sharing)


$ mvn --version
Apache Maven 3.9.11 (3e54c93a704957b63ee3494413a2b544fd3d825b)
Maven home: $HOME/.sdkman/candidates/maven/current
Java version: 21.0.8, vendor: Ubuntu, runtime: /usr/lib/jvm/java-21-openjdk-amd64
Default locale: ja_JP, platform encoding: UTF-8
OS name: "linux", version: "6.8.0-79-generic", arch: "amd64", family: "unix"

準備

まずはSpring Bootプロジェクトを作成します。依存関係は今回はwebにしました。

$ curl -s https://start.spring.io/starter.tgz \
  -d bootVersion=3.5.5 \
  -d javaVersion=21 \
  -d type=maven-project \
  -d name=structured-logging \
  -d groupId=org.littlewings \
  -d artifactId=structured-logging \
  -d version=0.0.1-SNAPSHOT \
  -d packageName=org.littlewings.spring.logging \
  -d dependencies=web \
  -d baseDir=structured-logging | tar zxvf -

ディレクトリー内に移動。

$ cd structured-logging

Maven依存関係などはこちら。

        <properties>
                <java.version>21</java.version>
        </properties>
        <dependencies>
                <dependency>
                        <groupId>org.springframework.boot</groupId>
                        <artifactId>spring-boot-starter-web</artifactId>
                </dependency>

                <dependency>
                        <groupId>org.springframework.boot</groupId>
                        <artifactId>spring-boot-starter-test</artifactId>
                        <scope>test</scope>
                </dependency>
        </dependencies>

        <build>
                <plugins>
                        <plugin>
                                <groupId>org.springframework.boot</groupId>
                                <artifactId>spring-boot-maven-plugin</artifactId>
                        </plugin>
                </plugins>
        </build>

自動生成されたJavaのソースコードは削除しておきます。

$ rm src/main/java/org/littlewings/spring/logging/StructuredLoggingApplication.java src/test/java/org/littlewings/spring/logging/StructuredLoggingApplicationTests.java

mainクラス。

src/main/java/org/littlewings/spring/logging/App.java

package org.littlewings.spring.logging;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App {
    public static void main(String... args) {
        SpringApplication.run(App.class, args);
    }
}

ログ出力入りのRestController。ロギングライブラリーは今回はSLF4J＋Logbackを対象にします。

src/main/java/org/littlewings/spring/logging/HelloController.java

package org.littlewings.spring.logging;

import java.util.Map;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RequestMapping("/hello")
@RestController
public class HelloController {
    private Logger logger = LoggerFactory.getLogger(HelloController.class);

    @GetMapping
    public Map<String, String> message(@RequestParam(required = false) String word) {
        String wordOrDefault = word == null ? "World" : word;

        logger.info("info logging");

        try (var ignored = MDC.putCloseable("word", wordOrDefault)) {
            logger.info("info logging with MDC");
        }

        logger.error("exception", new RuntimeException("Oops!!"));

        String message = String.format("Hello, %s!!", wordOrDefault);

        return Map.of("message", message);
    }
}

MDCやスタックトレースも含めておきました。

application.propertiesはひとまずデフォルトのままにしておきます。

src/main/resources/application.properties

spring.application.name=structured-logging

また今回はlogback-spring.xmlは使いません。

Logging / Custom Log Configuration

動作確認しましょう。起動。

$ mvn spring-boot:run

確認。

$ curl localhost:8080/hello
{"message":"Hello, World!!"}


$ curl localhost:8080/hello?word=Spring
{"message":"Hello, Spring!!"}

この時のログは、それぞれこんな感じです。

# curl localhost:8080/hello
2025-08-30T22:25:29.248+09:00  INFO 57400 --- [structured-logging] [nio-8080-exec-1] o.l.spring.logging.HelloController       : info logging
2025-08-30T22:25:29.248+09:00  INFO 57400 --- [structured-logging] [nio-8080-exec-1] o.l.spring.logging.HelloController       : info logging with MDC
2025-08-30T22:25:29.249+09:00 ERROR 57400 --- [structured-logging] [nio-8080-exec-1] o.l.spring.logging.HelloController       : exception

java.lang.RuntimeException: Oops!!
        at org.littlewings.spring.logging.HelloController.message(HelloController.java:27) ~[classes/:na]
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[na:na]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.44.jar:6.0]
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.44.jar:6.0]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at java.base/java.lang.Thread.run(Thread.java:1583) ~[na:na]


# curl localhost:8080/hello?word=Spring
2025-08-30T22:25:30.644+09:00  INFO 57400 --- [structured-logging] [nio-8080-exec-2] o.l.spring.logging.HelloController       : info logging
2025-08-30T22:25:30.644+09:00  INFO 57400 --- [structured-logging] [nio-8080-exec-2] o.l.spring.logging.HelloController       : info logging with MDC
2025-08-30T22:25:30.644+09:00 ERROR 57400 --- [structured-logging] [nio-8080-exec-2] o.l.spring.logging.HelloController       : exception

java.lang.RuntimeException: Oops!!
        at org.littlewings.spring.logging.HelloController.message(HelloController.java:27) ~[classes/:na]
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[na:na]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.44.jar:6.0]
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.2.10.jar:6.2.10]
        at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.44.jar:6.0]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.2.10.jar:6.2.10]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
        at java.base/java.lang.Thread.run(Thread.java:1583) ~[na:na]

デフォルトフォーマットなのでMDCに登録しても出力されていませんね。

2025-08-30T22:25:30.644+09:00  INFO 57400 --- [structured-logging] [nio-8080-exec-2] o.l.spring.logging.HelloController       : info logging with MDC

では、ここからフォーマットを構造化ログに変更してどうなるか見ていきましょう。

Spring Bootで構造化ログフォーマットでログ出力する

ここからはSpring Bootがサポートしている構造化ログフォーマットを使って、ログを出力していきます。

ソースコードは一切変更せず、application.propertiesのみの変更で見ていきます。

Elastic Common Schema（ECS）

まずはElastic Common Schema（ECS）から。

application.propertiesに以下を追加します。

logging.structured.format.console=ecs

起動。

$ mvn spring-boot:run

起動する時のログの時点で、すでにJSONフォーマットになっています。

{"@timestamp":"2025-08-30T13:29:24.175925265Z","log":{"level":"INFO","logger":"org.littlewings.spring.logging.App"},"process":{"pid":57692,"thread":{"name":"main"}},"service":{"name":"structured-logging","node":{}},"message":"Starting App using Java 21.0.8 with PID 57692 (/path/to/structured-logging/target/classes started by user in /path/to/structured-logging)","ecs":{"version":"8.11"}}
{"@timestamp":"2025-08-30T13:29:24.179901936Z","log":{"level":"INFO","logger":"org.littlewings.spring.logging.App"},"process":{"pid":57692,"thread":{"name":"main"}},"service":{"name":"structured-logging","node":{}},"message":"No active profile set, falling back to 1 default profile: \"default\"","ecs":{"version":"8.11"}}

curlでアクセスした時のログを載せておきます。

# curl localhost:8080/hello
{"@timestamp":"2025-08-30T13:30:21.470546361Z","log":{"level":"INFO","logger":"org.littlewings.spring.logging.HelloController"},"process":{"pid":57692,"thread":{"name":"http-nio-8080-exec-1"}},"service":{"name":"structured-logging","node":{}},"message":"info logging","ecs":{"version":"8.11"}}
{"@timestamp":"2025-08-30T13:30:21.470913331Z","log":{"level":"INFO","logger":"org.littlewings.spring.logging.HelloController"},"process":{"pid":57692,"thread":{"name":"http-nio-8080-exec-1"}},"service":{"name":"structured-logging","node":{}},"message":"info logging with MDC","word":"World","ecs":{"version":"8.11"}}
{"@timestamp":"2025-08-30T13:30:21.471258111Z","log":{"level":"ERROR","logger":"org.littlewings.spring.logging.HelloController"},"process":{"pid":57692,"thread":{"name":"http-nio-8080-exec-1"}},"service":{"name":"structured-logging","node":{}},"message":"exception","error":{"type":"java.lang.RuntimeException","message":"Oops!!","stack_trace":"java.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n"},"ecs":{"version":"8.11"}}


# curl localhost:8080/hello?word=Spring
{"@timestamp":"2025-08-30T13:30:22.879123867Z","log":{"level":"INFO","logger":"org.littlewings.spring.logging.HelloController"},"process":{"pid":57692,"thread":{"name":"http-nio-8080-exec-2"}},"service":{"name":"structured-logging","node":{}},"message":"info logging","ecs":{"version":"8.11"}}
{"@timestamp":"2025-08-30T13:30:22.879803069Z","log":{"level":"INFO","logger":"org.littlewings.spring.logging.HelloController"},"process":{"pid":57692,"thread":{"name":"http-nio-8080-exec-2"}},"service":{"name":"structured-logging","node":{}},"message":"info logging with MDC","word":"Spring","ecs":{"version":"8.11"}}
{"@timestamp":"2025-08-30T13:30:22.880349487Z","log":{"level":"ERROR","logger":"org.littlewings.spring.logging.HelloController"},"process":{"pid":57692,"thread":{"name":"http-nio-8080-exec-2"}},"service":{"name":"structured-logging","node":{}},"message":"exception","error":{"type":"java.lang.RuntimeException","message":"Oops!!","stack_trace":"java.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n"},"ecs":{"version":"8.11"}}

MDC入りのログレコードをフォーマットして表示しておきます。

{
  "@timestamp": "2025-08-30T13:30:22.879803069Z",
  "log": {
    "level": "INFO",
    "logger": "org.littlewings.spring.logging.HelloController"
  },
  "process": {
    "pid": 57692,
    "thread": {
      "name": "http-nio-8080-exec-2"
    }
  },
  "service": {
    "name": "structured-logging",
    "node": {}
  },
  "message": "info logging with MDC",
  "word": "Spring",
  "ecs": {
    "version": "8.11"
  }
}

Graylog Extended Log Format（GELF）

次はGraylog Extended Log Format（GELF）です。

application.propertiesのlogging.structured.format.consoleを以下のように変更。

logging.structured.format.console=gelf

アプリケーションを起動して、ログを確認してみます。起動時から構造化ログになっているのはECSと同じなのでこちらは割愛して、curlで
リクエストを受けた時のログのみ載せます。

# curl localhost:8080/hello
{"version":"1.1","short_message":"info logging","timestamp":1756560901.885,"level":6,"_level_name":"INFO","_process_pid":58384,"_process_thread_name":"http-nio-8080-exec-1","host":"structured-logging","_log_logger":"org.littlewings.spring.logging.HelloController"}
{"version":"1.1","short_message":"info logging with MDC","timestamp":1756560901.885,"level":6,"_level_name":"INFO","_process_pid":58384,"_process_thread_name":"http-nio-8080-exec-1","host":"structured-logging","_log_logger":"org.littlewings.spring.logging.HelloController","_word":"World"}
{"version":"1.1","short_message":"exception","timestamp":1756560901.886,"level":3,"_level_name":"ERROR","_process_pid":58384,"_process_thread_name":"http-nio-8080-exec-1","host":"structured-logging","_log_logger":"org.littlewings.spring.logging.HelloController","full_message":"exception\n\njava.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n","_error_type":"java.lang.RuntimeException","_error_stack_trace":"java.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n","_error_message":"Oops!!"}


# curl localhost:8080/hello?word=Spring
{"version":"1.1","short_message":"info logging","timestamp":1756560903.269,"level":6,"_level_name":"INFO","_process_pid":58384,"_process_thread_name":"http-nio-8080-exec-2","host":"structured-logging","_log_logger":"org.littlewings.spring.logging.HelloController"}
{"version":"1.1","short_message":"info logging with MDC","timestamp":1756560903.269,"level":6,"_level_name":"INFO","_process_pid":58384,"_process_thread_name":"http-nio-8080-exec-2","host":"structured-logging","_log_logger":"org.littlewings.spring.logging.HelloController","_word":"Spring"}
{"version":"1.1","short_message":"exception","timestamp":1756560903.269,"level":3,"_level_name":"ERROR","_process_pid":58384,"_process_thread_name":"http-nio-8080-exec-2","host":"structured-logging","_log_logger":"org.littlewings.spring.logging.HelloController","full_message":"exception\n\njava.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n","_error_type":"java.lang.RuntimeException","_error_stack_trace":"java.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n","_error_message":"Oops!!"}

フォーマットしたMDC入りのログレコード。

{
  "version": "1.1",
  "short_message": "info logging with MDC",
  "timestamp": 1756560903.269,
  "level": 6,
  "_level_name": "INFO",
  "_process_pid": 58384,
  "_process_thread_name": "http-nio-8080-exec-2",
  "host": "structured-logging",
  "_log_logger": "org.littlewings.spring.logging.HelloController",
  "_word": "Spring"
}

Logstash JSON format

最後はLogstash JSON formatです。

application.propertiesのlogging.structured.format.consoleを以下のように変更。

logging.structured.format.console=logstash

アプリケーションを起動して、ログを確認してみます。

# curl localhost:8080/hello
{"@timestamp":"2025-08-30T22:39:16.301734471+09:00","@version":"1","message":"info logging","logger_name":"org.littlewings.spring.logging.HelloController","thread_name":"http-nio-8080-exec-1","level":"INFO","level_value":20000}
{"@timestamp":"2025-08-30T22:39:16.30216843+09:00","@version":"1","message":"info logging with MDC","logger_name":"org.littlewings.spring.logging.HelloController","thread_name":"http-nio-8080-exec-1","level":"INFO","level_value":20000,"word":"World"}
{"@timestamp":"2025-08-30T22:39:16.30251357+09:00","@version":"1","message":"exception","logger_name":"org.littlewings.spring.logging.HelloController","thread_name":"http-nio-8080-exec-1","level":"ERROR","level_value":40000,"stack_trace":"java.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n"}



# curl localhost:8080/hello?word=Spring
{"@timestamp":"2025-08-30T22:39:17.388146518+09:00","@version":"1","message":"info logging","logger_name":"org.littlewings.spring.logging.HelloController","thread_name":"http-nio-8080-exec-2","level":"INFO","level_value":20000}
{"@timestamp":"2025-08-30T22:39:17.388965456+09:00","@version":"1","message":"info logging with MDC","logger_name":"org.littlewings.spring.logging.HelloController","thread_name":"http-nio-8080-exec-2","level":"INFO","level_value":20000,"word":"Spring"}
{"@timestamp":"2025-08-30T22:39:17.389536907+09:00","@version":"1","message":"exception","logger_name":"org.littlewings.spring.logging.HelloController","thread_name":"http-nio-8080-exec-2","level":"ERROR","level_value":40000,"stack_trace":"java.lang.RuntimeException: Oops!!\n\tat org.littlewings.spring.logging.HelloController.message(HelloController.java:27)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\n\tat java.base/java.lang.reflect.Method.invoke(Method.java:580)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:258)\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:191)\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:991)\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:896)\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)\n\tat jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769)\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)\n\tat java.base/java.lang.Thread.run(Thread.java:1583)\n"}

フォーマットしたMDC入りのログレコード。

{
  "@timestamp": "2025-08-30T22:39:17.388965456+09:00",
  "@version": "1",
  "message": "info logging with MDC",
  "logger_name": "org.littlewings.spring.logging.HelloController",
  "thread_name": "http-nio-8080-exec-2",
  "level": "INFO",
  "level_value": 20000,
  "word": "Spring"
}

だいたい雰囲気はわかったでしょうか。

並べてみる

雰囲気を比べるために、各フォーマットのログを並べておきます。

Elastic Common Schema（ECS）。

{
  "@timestamp": "2025-08-30T13:30:22.879803069Z",
  "log": {
    "level": "INFO",
    "logger": "org.littlewings.spring.logging.HelloController"
  },
  "process": {
    "pid": 57692,
    "thread": {
      "name": "http-nio-8080-exec-2"
    }
  },
  "service": {
    "name": "structured-logging",
    "node": {}
  },
  "message": "info logging with MDC",
  "word": "Spring",
  "ecs": {
    "version": "8.11"
  }
}

Graylog Extended Log Format（GELF）。

{
  "version": "1.1",
  "short_message": "info logging with MDC",
  "timestamp": 1756560903.269,
  "level": 6,
  "_level_name": "INFO",
  "_process_pid": 58384,
  "_process_thread_name": "http-nio-8080-exec-2",
  "host": "structured-logging",
  "_log_logger": "org.littlewings.spring.logging.HelloController",
  "_word": "Spring"
}

Logstash JSON format。

{
  "@timestamp": "2025-08-30T22:39:17.388965456+09:00",
  "@version": "1",
  "message": "info logging with MDC",
  "logger_name": "org.littlewings.spring.logging.HelloController",
  "thread_name": "http-nio-8080-exec-2",
  "level": "INFO",
  "level_value": 20000,
  "word": "Spring"
}

デフォルト設定や実装など

ドキュメントに書かれている構造化ログの設定例を見ると、こんな感じになっています。

<!-- replace your encoder with StructuredLogEncoder -->
<encoder class="org.springframework.boot.logging.logback.StructuredLogEncoder">
    <format>${CONSOLE_LOG_STRUCTURED_FORMAT}</format>
    <charset>${CONSOLE_LOG_CHARSET}</charset>
</encoder>

Logging / Structured Logging

CONSOLE_LOG_STRUCTURED_FORMAT（logging.structured.format.console）、
FILE_LOG_STRUCTURED_FORMAT（logging.structured.format.file）があるようですが、この値はなんなのでしょう？

定義を見ると、-のようです。

 <property name="CONSOLE_LOG_STRUCTURED_FORMAT" value="${CONSOLE_LOG_STRUCTURED_FORMAT:-}"/>


    <property name="FILE_LOG_STRUCTURED_FORMAT" value="${FILE_LOG_STRUCTURED_FORMAT:-}"/>

https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/resources/org/springframework/boot/logging/logback/defaults.xml

どうなっているかというと、それぞれの実装クラスでフォーマットが決まっている、ということみたいですね。

• https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/ElasticCommonSchemaStructuredLogFormatter.java
• https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/GraylogExtendedLogFormatStructuredLogFormatter.java
• https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/LogstashStructuredLogFormatter.java

これらのクラスはJsonWriterStructuredLogFormatterクラスを継承しており、StructuredLogFormatterインターフェースを実装しています。

https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/structured/JsonWriterStructuredLogFormatter.java

https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/structured/StructuredLogFormatter.java

自分でフォーマットを作る場合はStructuredLogFormatterインターフェースを実装すること、となっていましたが、同じ仕組みですね。

ちなみにカスタマイズの際は、こちらが使えるかも見ておいた方がよさそうです。

https://github.com/spring-projects/spring-boot/blob/v3.5.5/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/structured/StructuredLoggingJsonMembersCustomizer.java

おわりに

Spring Boot 3.4で追加された構造化ログ出力を試してみました。

機能が追加されたこと自体は知っていましたが、具体的にどういうものかまでちゃんと見ていなかったので今回ドキュメントからしっかり
確認しておいてどういうものかだいたいわかった気がします。

これからはSpring Bootで構造化ログを使う時は、この機能を使えばよさそうですね。依存関係も減らせますし。