Read a text file using java.util.Scanner

Scanner is a utility class that comes with Java SE since version 5.0. It lets you read a plain text file just like BufferReader, but more flexible. It can be customized so that you can read the contents line-by-line, word-by-word, or customized delimiter.

The readFileByLine method reads a plain text file one line at a time.

 public static void readFileByLine(String fileName) {
  try {
   File file = new File(fileName);
   Scanner scanner = new Scanner(file);
   while (scanner.hasNext()) {
    System.out.println(scanner.next());
   }
   scanner.close();
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  }
 }

The following method does the same as above except that it use a new line character as a delimiter.

 public static void readFileByLine(String fileName) {
  try {
   Scanner scanner = new Scanner(new File(fileName));
   scanner.useDelimiter(System.getProperty("line.separator"));
   while (scanner.hasNext())
    System.out.println(scanner.next());
   scanner.close();
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  }
 }

What if you want to read the entire text file at once? You can do so by setting the delimiter "\\z".

 public static void readFileByLine(String fileName) {
  try {
   Scanner scanner = new Scanner(new File(fileName));
   scanner.useDelimiter("\\z");
   System.out.println(scanner.next());
   scanner.close();
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  }
 }

scanner.useDelimiter("\\z"); means the same as
scanner.useDelimiter(Pattern.compile("\\z"));

By using the "\\z" delimiter, you can read the entire web page as an HTML string.

 public static void readWebPage(String url) {
  URLConnection connection;
  try {
   connection = new URL(url).openConnection();
   Scanner scanner = new Scanner(connection.getInputStream());
   scanner.useDelimiter("\\z");
   String text = scanner.next();
   System.out.println(text);
  } catch (MalformedURLException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }
 }

You can also use Scanner to read a semi-structured text file which stores data separated by tabs, commas, or semi-colons. For more information read this.

Consult java.util.regex.Pattern javadoc for other delimiters.