In terms of development, hadoop is first of all a platform to provide big data storage, so we need to use its storage function, so we need to master its data operation api(scala api or Java API); Secondly, hadoop is the data source of big data analysis, and it is familiar with the analysis/use methods of big data (spark/map-reduce technology, both scala and java APIs).
Therefore, learning hadoop must master a scala or java development language, and then learn hadoop data manipulation commands, api, spark/map-reduce analysis technology.
In addition, you can also learn hbase, a structured big data storage technology based on hdfs, and flume, a big data acquisition technology.