logback doesn't find maven's property project.build.directory

Question

I have a small project with Spring Boot and maven, and now I'm trying to configure logback to write to a file. I want it to write to a file given by ${project.build.directory}/${log.folder}/logfile.log, so a subfolder of the build directory, being ${log.folder} a property that I specify in an application.properties file, places under my /resources folder.

This is my logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/base.xml"/>
    <logger name="org.springframework.boot" level="INFO"/>
    <logger name="org.springframework.security" level="ERROR"/>
    <logger name="org.glassfish.jersey" level="DEBUG"/>

    <property resource="application.properties"/>

    <appender name="DUMMY_APPENDER" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>${project.build.directory}/${log.folder}/logfile.log</file>
        <encoder>
            <pattern>%d{"yyyy-MM-dd HH:mm:ss,SSS zzz"}, [%thread] %-5level %logger{5} - %msg%n
            </pattern>
        </encoder>
        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <fileNamePattern>${log.folder}/spring.log.%d</fileNamePattern>
        </rollingPolicy>
    </appender>

    <logger name="xxxxxx" level="INFO" additivity="false">
        <appender-ref ref="DUMMY_APPENDER"/>
    </logger>

    <root level="INFO">
        <appender-ref ref="DUMMY_APPENDER"/>
    </root>
</configuration>

It writes the logs, but my problem is that when I run the application, it creates a folder project.build.directory_IS_UNDEFINED, then places my log.folder under it. It says in the documentation, that

As its build tool, logback relies on Maven, a widely-used open-source build tool.

And when, in the logback.xml, I start typing ${pro... then my IDE displays a set of available maven implicit properties.

So it should work, but it doesn't. Any idea why?

Answer 1

It doesn't work due to what @luboskmac said.

Here is how to make it work. I have reproduced the problem and pushed up a solution here : https://github.com/ajorpheus/logback-maven/releases

Here is a summary of the fix : https://github.com/ajorpheus/logback-maven/commit/f245e5a6f4c13f9ba8e161c5452d296b653977d0

1. Define a property in the pom to hold the location of your logfile:

   

2. Use the property in the logback.xml appender:

3. Enable maven resource filtering so that any maven properties defined in the the resources being scanned are replaced with their corresponding values

Answer 2

${project.build.directory} is Maven's property, which is available only during the maven build. On the other hand, Logback is being used on runtime of the application. So obviously ${project.build.directory} is not defined on runtime.

You need to pick location which will be tailored to runtime environment and your deployment topology.