Microservices with SpringBoot migration

I'm trying to implement a microservice architecture starting from my monolithic architecture. the current implementation is composed by a certain number of executable jars called using a list of options (some mandatory and others optional); I was thinking to convert each of them in a service.  The idea is to build a sort of wrapper around of the current jar using springboot, adding one controller with a sort of start/stop to be called from outside for implementing the REST API interface , anyway it is not clear to me which is the best way, for an external app (or another service), to pass the list of options (I can pass a string or var=value structure but it looks heavy with many options). Can someone tell me which is the best way to do this migration, or if the idea to build a wrapper is wrong. Thanks a lot for the help.

Spring Boot doesn't a microservice make. In fact, you can bundle some distinctly non-micro services into Spring Boot. Spring Boot is just a convenient all-in-one bundling of a webapp server (e.g., Tomcat) with a webapp so that instead of the usual fuss about installing a webapp server and deploying an app into it, you have an all-in-one module.

However, Spring Boot and Containers are both (and often used together) handy ways of packaging up micro-services for quick and easy deployment.

If you have executable JARs and want to use them via ReST, the first step is then to build webapps based on them. Whether those webapps end up as micro-services of full-blown apps would depend on what your JARs contain.

The preferred way for a Tomcat server to provide custom options to a webapp is to set them up in webapp environment options as part of the deployment of the webapp so that JNDI code within the webapp can find and read them. I've not actually read up on how that would translate into Spring Boot, but I'd expect that the "-D" JVM command line options play a part.

Thanks a lot for the answer and you are right when you say springboot doesn't make microservices......anyway the idea is to convert a monolithic application composed by 7-8 executables (and a lot of shared libraries) in a system based on 7-8 services (each executable independent). So I thought the best way was to make for each executable (jar app) a standalone service called from a sort of MMI (orchestrator to use the microservice notation). Anyway in order to be able to start/stop the app I decided to wrap my original app in a springbootapp with web REST/API enabled (tomcat encapsulated). At this point it is clear I can call the old executable via web using the parameters needed for example the old:

java -jar target/foo.jar -i abc                                                                                      
Missing required option: o
usage: utility-name
-i,--input <arg>    input file path
-o,--output <arg>   output file

in the simple case and after defined the controller:
http://localhost/foo?input=aaa&output=bbb

But what to do when the number of app options is high? Is there another way to perform the migration?