Java in a Nutshell, 8th Edition

Chapter 10. File Handling and I/O

Java has had input/output (I/O) support since the very first version. However, due to Java’s strong desire for platform independence, the earlier versions of I/O functionality emphasized portability over functionality. As a result, they were not always easy to work with.

We’ll see later in the chapter how the original APIs have been supplemented—they are now rich, fully featured, and very easy to develop with. Let’s kick off the chapter by looking at the original, “classic” approach to Java I/O, which the more modern approaches layer on top of.

Classic Java I/O

The File class is the cornerstone of Java’s original way to do file I/O. This abstraction can represent both files and directories but in doing so is sometimes a bit cumbersome to deal with, leading to code like this:

// Get a file object to represent the user's home directory
var homedir = new File(System.getProperty("user.home"));

// Create an object to represent a config file (should
// already be present in the home directory)
var f = new File(homedir, "app.conf");

// Check the file exists, really is a file, and is readable
if (f.exists() && f.isFile() && f.canRead()) {

  // Create a file object for a new configuration directory
  var configdir = new File(homedir, ".configdir");
  // And create it
  configdir.mkdir();

  // Finally, move the config file to its new home
  f.renameTo(new File(configdir, ".config"));
}

This shows some of the flexibility possible with the File class, but it also ...