Log4j 2 JSON Configuration

问题:

I have a configuration in XML that I would like to convert to JSON. The JSON version is not being loaded by Log4j and I cannot find any typos. My test code simply logs an ERROR level and a DEBUG level message. Only ERROR messages are being displayed and no file output is being generated - I'm assuming the framework falls back to the default initialization instead of the JSON file.

Note: The log4j2-test.json file is on the classpath.

I'm using apache-log4j-2.0-beta9 binary found here.

The XML configuration is the following:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration name="Test">
    <Properties>
        <Property name="Directory">${sys:user.home}/logs</Property>
        <Property name="Filename">test.log</Property>
    </Properties>
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
        <RollingFile name="File" 
            fileName="${Directory}/${Filename}" 
            filePattern="${Directory}/${date:yyyy-MM}/test-%d{MM-dd-yyyy}-%i.log.gz">
            <PatternLayout>
                <pattern>%d %p %logger{36} [%t] %m%n</pattern>
            </PatternLayout>
            <Policies>
                <SizeBasedTriggeringPolicy size="1 MB"/>
            </Policies>
            <DefaultRolloverStrategy max="10"/>
        </RollingFile>
    </Appenders>
    <Loggers>
        <Root level="debug">
            <AppenderRef ref="Console"/>
            <AppenderRef ref="File"/>
        </Root>
    </Loggers>
</Configuration>

and the JSON configuration is:

{
   "configuration": {
      "name": "Default",
      "properties": {
         "property": {
            "name":"Directory",
            "value":"${sys:user.home}/logs"
         },
         "property": {
            "name":"FileName",
            "value":"test.log"
         }
      },
      "appenders": {
         "Console": {
            "name":"Console",
            "target":"SYSTEM_OUT",
            "PatternLayout": {
               "pattern":"%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"
            }
         },
         "RollingFile": {
            "name":"File",
            "fileName":"${Directory}/${FileName}",
            "filePattern":"${Directory}/${date:yyyy-MM}/test-%d{MM-dd-yyyy}-%i.log.gz",
            "PatternLayout": {
               "pattern":"%d %p %logger{36} [%t] %m%n"
            },
            "Policies": {
               "SizeBasedTriggeringPolicy": {
                  "size":"1 MB"
               }
            },
            "DefaultRolloverStrategy": {
               "max":"10"
            }
         }
      },
      "loggers": {
         "root": {
            "level":"debug",
            "appender-ref": {
               "ref":"Console"
            },
            "appender-ref": {
              "ref":"File"
            }
         }
      }
   }
}

回答1:

I found a solution to the problem.

It turns out that the Log4j 2 Configuration doesn't document all the required dependencies:

The JSON support uses the Jackson Data Processor to parse the JSON files. These dependencies must be added to a project that wants to use JSON for configuration:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.8.7</version>
</dependency>

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.7</version>
</dependency>

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.8.7</version>
</dependency>

回答2:

I believe that I have an additional correction to the JSON configuration that was posted. For me, this part produces problems:

  "properties": {
     "property": {
        "name":"Directory",
        "value":"${sys:user.home}/logs"
     },
     "property": {
        "name":"FileName",
        "value":"test.log"
     }
  },

On my setup, this will output ~/logs/${FileName} or ~/${Directory}/test.log, which means that it is only interpolating one of the properties instead of both.

I concluded from this that the properties were not specified correctly in JSON form. To fix it, I specified the properties as a JSON array

    "properties": {
        "property": [{
            "name":"Directory",
            "value":"${sys:user.home}/logs"
        },
        {
            "name":"FileName",
            "value":"test.log"
        }]
    },

With this in place, it seems to fix the problem and correctly outputs to ~/logs/test.log

My setup is log4j2 2.0.2 on Mac with tomcat 7.0.55

回答3:

You have another flaw in there that might catch you, that I've run into with log4j json.

"appender-ref": {
    "ref":"Console"
},
"appender-ref": {
    "ref":"File"
}

Try this instead, as it is now, it will only catch one appender.

"appender-ref": [{
    "ref":"Console"
},
{
    "ref":"File"
}]