in log4j2-ecs-layout/src/main/java/co/elastic/logging/log4j2/EcsLayout.java [291:307]
private void serializeSimpleMessage(StringBuilder builder, boolean gcFree, Message message, Throwable thrown) {
builder.append("\"message\":\"");
if (message instanceof CharSequence) {
JsonUtils.quoteAsString(((CharSequence) message), builder);
} else if (gcFree && message instanceof StringBuilderFormattable) {
final StringBuilder messageBuffer = EcsJsonSerializer.getMessageStringBuilder();
try {
((StringBuilderFormattable) message).formatTo(messageBuffer);
JsonUtils.quoteAsString(messageBuffer, builder);
} finally {
trimToMaxSizeCopy(messageBuffer);
}
} else {
JsonUtils.quoteAsString(EcsJsonSerializer.toNullSafeString(message.getFormattedMessage()), builder);
}
builder.append("\", ");
}