[JAVA] Output Spring Boot log in json format

reference

JSON Logging for Spring Boot After that, the contents implemented according to the above article are posted. The above article has more information, so if you are not comfortable with English, we recommend that you refer to it.

Execution environment

• Java12
• SpirngBoot 2.1.7.RELEASE
• Gradle 5.6

Preparation

Added logstash to dependencies

build.gradle

dependencies {
	implementation 'net.logstash.logback:logstash-logback-encoder:6.1'
}

Added logback settings

src/main/resources/logback-spring.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <property resource="application.yml" />
    <contextName>${spring.application.name}</contextName>
    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
            <providers>
                <timestamp>
                    <fieldName>timeStamp</fieldName>
                    <timeZone>UTC</timeZone>
                </timestamp>
                <loggerName>
                    <fieldName>logger</fieldName>
                </loggerName>
                <logLevel>
                    <fieldName>level</fieldName>
                </logLevel>
                <threadName>
                    <fieldName>thread</fieldName>
                </threadName>
                <mdc />
                <message>
                    <fieldName>message</fieldName>
                </message>
                <arguments>
                    <includeNonStructuredArguments>false</includeNonStructuredArguments>
                </arguments>
                <stackTrace>
                    <fieldName>stack</fieldName>
                </stackTrace>
            </providers>
        </encoder>
    </appender>
    <root level="INFO">
        <appender-ref ref="CONSOLE" />
    </root>
</configuration>

Implementation

Example of outputting INFO log in Controller class

• Logger acquisition is left to lombok's @ Slf4j annotation.

TestController.java

package com.exsample.controller;

import lombok.extern.slf4j.Slf4j;
import org.slf4j.MDC;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import static net.logstash.logback.argument.StructuredArguments.v;

@Slf4j
@RestController
@RequestMapping("/test")
public class TestController {
    @GetMapping
    public void get() {
        MDC.put("MDC key","MDC value");
        log.info("JSON Log",v("arg key","arg value"));
    }
}

result

The following log is output

{"timeStamp":"2019-08-28T08:52:22.173Z","logger":"com.exsample.controller.TestController","level":"INFO","thread":"main","MDC key":"MDC value","message":"JSON Log","arg key":"arg value"}

Supplement

• The contents set in the <encoder> tag of logback-spring.xml are output in order from the top.

(Excerpt) logback-spring.xml

<providers>
  <timestamp>
    <fieldName>timeStamp</fieldName>
    <timeZone>UTC</timeZone>
  </timestamp>
  <loggerName>
    <fieldName>logger</fieldName>
  </loggerName>
  <logLevel>
    <fieldName>level</fieldName>
  </logLevel>
  <threadName>
    <fieldName>thread</fieldName>
  </threadName>
  <mdc />
  <message>
    <fieldName>message</fieldName>
  </message>
  <arguments>
    <includeNonStructuredArguments>false</includeNonStructuredArguments>
  </arguments>
  <stackTrace>
    <fieldName>stack</fieldName>
  </stackTrace>
</providers>

Log contents

{
  "timeStamp": "2019-08-28T08:52:22.173Z",
  "logger": "com.exsample.controller.TestController",
  "level": "INFO",
  "thread": "main",
  "MDC key": "MDC value",
  "message": "JSON Log",
  "arg key": "arg value"
}

• The contents of MDC.put () are output at the position of the <mdc /> tag.

(Excerpt) TestController.java

MDC.put("MDC key","MDC value");

Log excerpt

"MDC key": "MDC value"

• The content passed to the first argument of log.info () is output at the position of the <message> tag.

(Excerpt) TestController.java

log.info("JSON Log",v("arg key","arg value"));

Log excerpt

"message": "JSON Log"

• If you pass StructuredArguments.v (key, value) after the second argument of log.info (), the contents will be output at the position of the <arguments> tag.

(Excerpt) TestController.java

log.info("JSON Log",v("arg key","arg value"));

Log excerpt

"arg key": "arg value"