public static boolean isInstalled() {
        java.util.logging.Logger rootLogger = getRootLogger();
        Handler[] handlers = rootLogger.getHandlers();
        for (Handler handler : handlers) {
            if (handler instanceof SLF4JBridgeHandler) {
                return true;
            }
        }
        return false;
    }
Returns true if SLF4JBridgeHandler has been previously installed, returns false otherwise.

@return true if SLF4JBridgeHandler is already installed, false otherwise
jul-to-slf4j/src/main/java/org/slf4j/bridge/SLF4JBridgeHandler.java