Escalog

Allows to log in logfmt format with logback. See https://brandur.org/logfmt for more information about logfmt.

It provides :

• A logback layout that format
• A slf4j compliant class that allows to use key-value pairs in your logs

It uses markers (org.slf4j.Marker) to define key-value pairs so it can seamlessly work with slf4j.

Installation

        <dependency>
            <groupId>com.batch.escalog</groupId>
            <artifactId>logging</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>

To log using escalog, use LogFmtLayout in your logback.xml. Here is an example which outputs to stdout in logfmt format :

<configuration>

    <appender name="stdout" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
            <layout class="com.batch.escalog.LogFmtLayout">
                <AppName>My Application Name</AppName>  <!-- optional. sets the key-value : 'app="MyApplication Name"' -->
            <layout/>
        </encoder>
    </appender>

</configuration>

Usage

Using LogFmt logger

The logger LogFmt is built on top of slf4j Logger, it provides all of its methods and additional logfmt specific methods. Here is an example of how you can use it :

LogFmt logger = LogFmt.from(LoggerFactory.getLogger(LogFmtLayoutTest.class));

logger.with("key1", "value1").and("key2", "value2").info("Everything is {}", "ok");
// time="2017-12-06T14:12:17" level=info package=com.batch.escalog module=LogFmtTest thread=main msg="Everything is ok" key1=value1 key2=value2

Using slf4j logger

The same can also be done with slf4j Logger using LogFmtMarker :

LogFmt logger = LoggerFactory.getLogger(LogFmtLayoutTest.class);

logger.info(LogFmtMarker.with("key1", "value1").and("key2", "value2") ,"Everything is {}", "ok");
// time="2017-12-06T14:12:17" level=info package=com.batch.escalog module=LogFmtTest thread=main msg="Everything is ok" key1=value1 key2=value2

Using MDC

LogFmt logger = LoggerFactory.getLogger(LogFmtLayoutTest.class);

MDC.put("key3", "value3");
logger.info(LogFmtMarker.with("key1", "value1").and("key2", "value2") ,"Everything is {}", "ok");
// time="2017-12-06T14:12:17" level=info package=com.batch.escalog module=LogFmtTest thread=main msg="Everything is ok"  key3=value3 key1=value1 key2=value2

Native key-value pairs

Here is the list of native key-value pairs that are automatically added.

Key	Description
time	date of the log (RFC3339 format)
level	log level : error,warning,info,debug,trace,all
msg	given message
app	app name (if provided)
thread	thread name
error	exception (if provided) : ex: logger.error(new Exception("error"), "Something went wrong")
package	Java package
module	Java class

Configuration

Escalog allows to configure the log entries by adding parameters to logback.xml.

Field

The parameter Field allows to specify which fields will be logged, and the order.

<layout class="com.batch.escalog.LogFmtLayout">
    <Fields>module, package, time, msg, mdc, custom</Fields>
</layout>

Here is an output example :

module=MyClass package=com.foo.bar time="2017-12-06T14:12:17" mdcKey1=mdcValue1 mdcKey2=mdcValue2 key1=value1 key2=value2

The available fields are the native keys, plus the following :

Key	Description
custom	key-values added with LogFmt or LogFmtMarker
mdc	key-values added with MDC

TimeFormat

The parameter TimeFormat allows to specify the format of the time field. It supports all the formats accepted by SimpleDateFormat

<layout class="com.batch.escalog.LogFmtLayout">
    <TimeFormat>YYYYMMdd`T`hh:mm:ss</TimeFormat>
</layout>

TODO

• Configuration : enable or disable key-values (native, MDC, additional key-values); specify order and fields format (time, exception, etc)