Error on pipeline configuration with Java plugin

Elastic Stack Logstash
1

Hi. I wrote a filter plugin in Java named blob_to_clob_filter. When using it in a pipeline I get the following error:
[2019-08-23T11:20:38,254][DEBUG][logstash.plugins.registry] On demand adding plugin to the registry {:name=>"blob_to_clob_filter", :type=>"filter", :class=>LogStash::Filters::BlobToClobFilter}
[2019-08-23T11:20:38,285][FATAL][logstash.runner ] The given configuration is invalid. Reason: java.lang.reflect.InvocationTargetException
[2019-08-23T11:20:38,300][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
The main class implements co.elastic.logstash.api.Filter
When running it in another machine i get
[2019-08-23T11:47:14,859][FATAL][logstash.runner ] The given configuration is invalid. Reason: Cannot start the Java plugin 'blob_to_clob_filter' in the Ruby execution engine. The Java execution engine is required to run Java plugins.
[2019-08-23T11:47:14,884][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
So maybe I have the same issue on the two machines.
How can I install the execution engine? One of the two machines has no internet access.

EDIT: it was a bug on the "Test and exit" mode, according to this topic on GitHub:

2

The java execution engine is enable by 'pipeline.java_execution: true' in logstash.yml (assuming you have a logstash version new enough to support it). It is on by default in v7.