Add json object to log4j2 when is JSONLayout

This doesn't seem possible to do with the built-in JsonLayout. No matter what I try it just does a toString on the field rather than serializing it correctly.

One solution is to use the PatternLayout and format it like JSON.

log4j.appender.frontEndAudit.layout=org.apache.log4j.PatternLayoutlog4j.appender.frontEndAudit.layout.ConversionPattern={"timestamp": "%d{MM/dd/yyyy HH:mm:ss:SSSS}", "class": "%C", "file": "%F", "level" : "%5p", "line_number" : "%L", "logger_name": "frontEndAuditLog", "mdc": "ipAddress": "%X{ipAddress}", "requestId":"%X{requestId}", "sessionId":"%X{sessionId}"}, "message": %m, "method": "%M", "source_host":"%X{sourceHost}", "thread_name": "%t" }%n

This was for log4j1 but same concept would work for log4j2

It turns out LogstashLayout is a custom layout that does the trick.

1. Write "message": "${json:message:json}" in LogstashJsonEventLayoutV1.json file.
2. You have to log a Java object which implements the MultiformatMessage and return the JSON string in getFromattedMessage method.
3. getMessageFormats() method also must return JSON.

log4j-layout-template-json is available with version 2.14.0 and works flawlessly using MapMessage.Just add below gradle dependencies if using gradle

compile 'org.apache.logging.log4j:log4j-api:2.14.0'compile 'org.apache.logging.log4j:log4j-core:2.14.0'compile 'org.apache.logging.log4j:log4j-layout-template-json:2.14.0'compile 'com.fasterxml.jackson.dataformat:jackson-dataformat-yaml:2.10.0'compile 'com.fasterxml.jackson.dataformat:jackson-databind:2.10.0'

log4j2.yaml looks like

Configuration:  name: Default  Appenders:   Console:    name: LogToConsole    target: SYSTEM_OUT        JsonTemplateLayout:      eventTemplateUri: "classpath:LogstashJsonEventLayoutV1.json"  Loggers:   AsyncRoot:      level: info     additivity: false     AppenderRef:         - ref: LogToConsole

Then extend MapMessage for the object(MyMapMessage) you want to log and use

private static final org.apache.logging.log4j.Logger LOGGER = LogManager.getLogger(YourClass.class);LOGGER.error(myMapMessage.getData());