Reading input data

Being able to read data is the most important skill for a data scientist, and this data is usually in text format, be it TXT, CSV, or any other format. In Java I/O API, the subclasses of the Reader classes deal with reading text files.

Suppose we have a text.txt file with some sentences (which may or may not make sense):

• My dog also likes eating sausage
• The motor accepts beside a surplus
• Every capable slash succeeds with a worldwide blame
• The continued task coughs around the guilty kiss

If you need to read the whole file as a list of strings, the usual Java I/O way of doing this is using BufferedReader:

List<String> lines = new ArrayList<>(); 

try (InputStream is = new FileInputStream("data/text.txt")) { 
    try (InputStreamReader isReader = new InputStreamReader(is,
               StandardCharsets.UTF_8)) { 
        try (BufferedReader reader = new BufferedReader(isReader)) { 
            while (true) { 
                String line = reader.readLine(); 
                if (line == null) { 
                    break; 
                } 
                lines.add(line); 
            } 

            isReader.close(); 
        } 
    } 
}

It is important to provide character encoding--this way, the Reader knows how to translate the sequence of bytes into a proper String object. Apart from UTF-8, there are UTF-16, ISO-8859 (which is ASCII-based text encoding for English), and many others.

There is a shortcut to get BufferedReader for a file directly:

Path path = Paths.get("data/text.txt"); 
try (BufferedReader reader = Files.newBufferedReader(path,
        StandardCharsets.UTF_8)) { 
    // read line-by-line 
}

Even with this shortcut, you can see that this is quite verbose for such a simple task as reading a list of lines from a file. You can wrap this in a helper function, or instead use the Java NIO API, which gives some helper methods to make this task easier:

Path path = Paths.get("data/text.txt"); 
List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8); 
System.out.println(lines);

The Java NIO shortcuts work only for files. Later, we will talk about shortcuts that work for any InputStream objects, not just files.