how to download component data into the local file system from a stream

 I can only suggest my blog: https://rsjazz.wordpress.com/
The Jazz Community http://jazz-community.org/ and the projects there. 

If you have run the Extensions Workshop, you have run the WorkshopSetup, which does the inverse of what you want to try. 
The use case you describe, or at least close is in https://github.com/jazz-community/ewm-scm-utils in https://github.com/jazz-community/ewm-scm-utils/blob/master/com.ibm.js.team.scm.supporttools/src/main/java/com/ibm/js/team/supporttools/scmutils/commands/DownloadComponentBaseline.java

The jar file is here: https://github.com/jazz-community/ewm-scm-utils/releases/tag/V2.7.1

You can run the tools in an Eclipse EWM RTC SDK workshop. Download the code, import into the SDK workshop, add the user library for the Palin Java client libraries and use the launches.

See https://jazz.net/library/article/1000 the version 7.x lab 1.10 SET UP A WORKSPACE FOR PLAIN JAVA CLIENT LIBRARY DEVELOPMENT.

Or follow https://github.com/jazz-community/ewm-scm-utils/blob/master/com.ibm.js.team.scm.supporttools/ReadMe%20-%20HowToRelease.txt and create a release on your own, which requires the steps before.  

I have tried to explain the process to setup for the plain Java Client Libraries a bit more detailed in https://github.com/jazz-community/work-item-command-line?tab=readme-ov-file#prerequisites