Download logstash codebase from https://github.com/elastic/logstash, and compile using gradle assemble. Configure gradle.properties file point to your newly built logstash-core directory.

Execute gradle gem command to build the plugin. Inside your logstash (pre-built) execute:

bin/logstash-plugin install --no-verify --local /path/to/logstash-output-logstash_jdbc_output_plugin-1.0.0.gem