You don't need to use Java code to decompress zip files with Mule 4. You can use the Mule Compression Module to compress/decompress zip or gzip files. The documentation has examples.
Extracted from documentation:
<compression:extract doc:name="Extract" >
<compression:extractor >
<compression:zip-extractor />
</compression:extractor>
</compression:extract>
<foreach doc:name="For Each" collection="payload">
<file:write doc:name="Write" config-ref="File_Config" path='#[output application/json
---
"output/" ++ (payload pluck $$)[0]]' >
<file:content ><![CDATA[#[output application/java --- ( payload pluck $ )[0]]]]></file:content>
</file:write>
</foreach>