Workaround for Dropwizard / logback / newrellic issue

PreMain.java

package no.ngt.tech.slf4jwait;

import org.slf4j.LoggerFactory;
import org.slf4j.helpers.SubstituteLoggerFactory;

import java.lang.reflect.Method;
import java.util.Arrays;


/**
 * Dropwizard uses both slf4j and logback.
 * In its bootstrap-code it gets a logger via slf4j and casts it to logback.
 * This can fail if slf4j / logback is not yet initialized properly.
 * This mostly happens when using newrelic which slows the initialization process down.
 *
 * By using this PreMain-main-class we will wait to start the real app until slf4j / logback is properly inited.
 *
 * How to use it:
 *
 * If you normally start your app like this:
 *
 *      com.ngt.MyMainClass arg1 arg 2
 *
 * You can use PreMain like this:
 *
 *      no.ngt.tech.slf4jwait.PreMain com.ngt.MyMainClass arg1 arg 2
 *
 */
public class PreMain {
    static {
        System.out.println("Waiting for slf4j to finish initialization");
        while ( LoggerFactory.getILoggerFactory() instanceof SubstituteLoggerFactory){
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                break;
            }
        }
    }


    public static void main(String[] args) throws Exception {
        String realMainClass = args[0];
        System.out.println("slf4j initialization finished - Starting mainClass: " + realMainClass);
        String[] realArgs = Arrays.copyOfRange(args, 1, args.length);
        Class mainClass = PreMain.class.getClassLoader().loadClass(realMainClass);
        Method mainMethod = mainClass.getMethod("main", String[].class);
        mainMethod.invoke(null, (Object)realArgs);
    }
}