Rest api File Download ( file created with data from database)

First of all, make a header row. and add body rows inserting data. At last, return converting the file to byte[].

CSV download (Apache commons-csv)

Add in build.gradle.

compile ('org.apache.commons:commons-csv:1.9.0')

Excel download (Apache POI(Poor Obfuscation Implement))

Add in build.gradle.

compile('org.apache.poi:poi:3.17')
compile('org.apache.poi:poi-ooxml:3.17')