Starting two spring applications in same JVM results in doubled log lines

Question

I've tried to start two Spring applications in the same JVM which worked fine except that now every log line is written twice, so in case of log line that are written for both applications are written four times effectivly.

I've also tried to see what appenders are attached to the loggers an I got STDOUT two times in it which would explain the behaviour.

It seems like starting spring twice ends up initializing logback twice without resetting the first initialization.

Is there some way to suppress this behaviour? I didn't even think that spring would manually initialize it.

The code I used to start the two applications (Main and SecondaryMain are in two indepenant packages, neither contained in the other):

    public static void main(String[] args) throws Exception
    {
        run("App1", Main.class, args);
        run("App2", SecondMain.class, args);
    }

    private static void run(String name, Class<?> clazz, String[] args)
    {
        SpringApplication run = new SpringApplication(clazz);

        ThreadGroup threadGroup = new ThreadGroup(name);
        Thread t = new Thread(threadGroup, () -> {run.run(args);}, name+".Main");
        t.start();
    }

My logback configuration (nothing special):

<configuration>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd' 'HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>
    <root level="info">
        <appender-ref ref="STDOUT" />
    </root>
</configuration>

Answer 1

In the meanwhile I've found two ways to accomplish it

disabling logging management in spring

One can specify the logging system that spring should use but there's also the option none so it won't set up any itself and that way also not twice

The con is that it won't integrate logging, in my case some components that used to log to logback suddenly didn't.

using a parent context

If both applications share a parent contract spring will only initialize logging once

This seems to be the cleaner solution and I haven't seen a con to it yet