public boolean isConnected(String remoteAddr) {
        ensureStarted();
        Url url = this.rpcRemoting.addressParser.parse(remoteAddr);
        return this.isConnected(url);
    }
check whether a client address connected

@param remoteAddr remote address
@return {@code true} means url is connected and {@code false} means disconnected.
src/main/java/com/alipay/remoting/rpc/RpcServer.java