Does log4j support JSON format?

just use buildin PatternLayout is ok:

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.encoding=UTF-8
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern={"debug_level":"%p","debug_timestamp":"%d{ISO8601}","debug_thread":"%t","debug_file":"%F", "debug_line":"%L","debug_message":"%m"}%n

will out put like:

{
    "debug_level" : "INFO",
    "debug_timestamp" : "2016-05-26 16:37:08,938",
    "debug_thread" : "main",
    "debug_file" : "TestLogOutPut.java",
    "debug_line" : "316",
    "debug_message" : "hello i am a log message"
}

this is official JSON layout

https://github.com/logstash/log4j-jsonevent-layout

1) Add maven dependency https://mvnrepository.com/artifact/net.logstash.log4j/jsonevent-layout

<dependency>
    <groupId>net.logstash.log4j</groupId>
    <artifactId>jsonevent-layout</artifactId>
    <version>1.7</version>  
</dependency>

2) Add configuration to your log4j.properties file

 log4j.rootCategory=WARN, RollingLog
 log4j.appender.RollingLog=org.apache.log4j.DailyRollingFileAppender
 log4j.appender.RollingLog.Threshold=TRACE
 log4j.appender.RollingLog.File=api.log
 log4j.appender.RollingLog.DatePattern=.yyyy-MM-dd
 log4j.appender.RollingLog.layout=net.logstash.log4j.JSONEventLayoutV1