In the NIFI UI , I dont find anywhere to save the data flow and create a new one.
Does NIFI support multiple data flow？
Yes. Although there is only one canvas when you open the WebUI that canvas ca have many logical dataflows. Typically you can organize each logical dataflow into a process group, and then start and stop the whole process group. Also you can give / limit permissions to the process groups for different users/groups to allow multiple teams to share the same NIFI Instance/Cluster.
Here is the link to the docs:
There is a very good article about how to use the process groups as reusable components:
And please be aware that the WebUI/Canvas is the IDE against the NIFI instance / cluster. You are directly working on the NIFI instance, it is not an remote modelling approach where you will have to deploy to the server after having finished your development. All you model and do is done directly on the NIFI instance.
Regarding saving the data flow, nifi saves everything in real-time. To save a flow outside of nifi then download the flow as a template. This is an xml file that can be uploaded again to nifi to restore the flow from its saved state. You can save any part of the flow as a template ... this can be a process group, or a highlighted full or partial flow.
This article may add some color: https://community.hortonworks.com/articles/60868/enterprise-nifi-implementing-reusable-components-a....