private String extractMainClassFromArchive(JarFile bootstrapJar) throws IOException {
        String mainClassFromManifest = bootstrapJar.getManifest().getMainAttributes().getValue(MANIFEST_MAIN_CLASS_KEY);
        if (mainClassFromManifest == null) {
            return NOT_FOUND;
        }
        return mainClassFromManifest;
    }
Returns the fully qualified class name of the application's main class.

@return the fully qualified class name of the main class, or an empty string if the main class cannot be resolved
agent-module/bootstraps/bootstrap-core/src/main/java/com/navercorp/pinpoint/bootstrap/resolver/condition/MainClassCondition.java