logback.xml is evaluated before application.yml is

Question

I'm building a web application using spring-boot 1.2.2.RELEASE.

I want to configure the logback output according to the value of the property "spring.profiles.active".

That property is defined in application.yml and lockback configuration is described in logback.xml.

But I found logback.xml is evaluated before application.yml is evaluated.

How can I start a SpringApplication reading application.yml before logback.xml?

Here is my Application.java.

/**
 * Application.java --
 */
package my.project;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).run(args);
    }

}

When I write the logback.xml in some bad format like this,

<?xml version="1.0" encoding="UTF-8"?>
aaa

Spring-boot reports an error which shows logback.xml is read in the constructor of SpringApplicationBuilder.

ERROR in ch.qos.logback.core.joran.event.SaxEventRecorder@449b193b - XML_PARSING - Parsing fatal error on line 2 and column 1 org.xml.sax.SAXParseException; lineNumber: 2; columnNumber: 1;
        [snip]
        at      at org.apache.commons.logging.impl.SLF4JLogFactory.getInstance(SLF4JLogFactory.java:155)
        at      at org.apache.commons.logging.impl.SLF4JLogFactory.getInstance(SLF4JLogFactory.java:132)
        at      at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:275)
        at      at org.springframework.boot.SpringApplication.<init>(SpringApplication.java:160)
        at      at org.springframework.boot.builder.SpringApplicationBuilder.createSpringApplication(SpringApplicationBuilder.java:96)
        at      at org.springframework.boot.builder.SpringApplicationBuilder.<init>(SpringApplicationBuilder.java:84)
        at      at my.project.Application.main(Application.java:13)
        [snip]

On the other hand, when I put the application.yml in some bad format by adding tab character, Spring-boot reports an error which shows it is read in the method 'run'.

Caused by: while scanning for the next token
found character          '\t(TAB)' that cannot start any token. (Do not use \t(TAB) for indentation)
 in 'reader', line 1, column 1:
        [snip]
        at org.springframework.boot.context.config.ConfigFileApplicationListener.onApplicationEvent(ConfigFileApplicationListener.java:126)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:151)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:128)
        at org.springframework.boot.context.event.EventPublishingRunListener.publishEvent(EventPublishingRunListener.java:100)
        at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:59)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:285)
        at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:139)
        at my.project.Application.main(Application.java:13)

Answer 1

How can I start a SpringApplication reading application.yml before logback.xml

You can't.

The Logback configuration is read very early so that logging is available for the rest of the initialisation process. There's then a second stage where Logback is reconfigured based on some of the configuration in application.yml.

Logging frameworks don't understand application.yml or Spring's Environment so certain properties are copied over the system properties which you can then reference in your Logback configuration. Those properties are logging.file and logging.path which are copied to LOGGING_FILE and LOGGING_PATH respectively. See the Spring Boot documentation for some more information.

There's also an open issue to allow more of the logging configuration to be performed in application.yml.