When you create a pipeline, you often need to read data from some external source, such as a file or a database. Likewise, you may want your pipeline to output its result data to an external storage system. Beam provides read and write transforms for a number of common data storage types. If you want your pipeline to read from or write to a data storage format that isn’t supported by the built-in transforms, you can implement your own read and write transforms.
To read a PCollection from one or more text files, use TextIO.read() to instantiate a transform and use TextIO.Read.from(String) to specify the path of the file(s) to be read.
Kata: Read the 'countries.txt' file and convert each country name into uppercase.
Use
TextIO and its corresponding
TextIO.read() method.
Refer to the Beam Programming Guide
"Reading input data" section for more information.