"After all, the engineers only needed to refuse to fix anything, and modern industry would grind to a halt." -Michael Lewis

For Doers

Java IO: Creating and Traversing Files And Directories

2018-11-03

You can view the sample code associated with this post on Github

Using the static methods in the Files class, a member of the java.nio.file package, we can manipulate the file system reasonably easily.

We can create an input stream, in exactly the same way as we do with an explicit constructor, like:

@Test
public void files_inputStreaming() throws Exception {
    Path pathToExampleFile = Paths.get(Utils.simpleExampleFilePath);

    try (InputStream inputStream = Files.newInputStream(pathToExampleFile)) {
        int readValue = inputStream.read();

        assertEquals('t', readValue);
    }
}

You can create a directory with the Files.createDirectory(..) method:

@Test
public void creatingDirsAndFiles_ex() throws Exception {
    Path pathToNewDir = Paths.get(Utils.pathToResources + "new-directory-to-create");

    Files.deleteIfExists(pathToNewDir);

    assertFalse(Files.isDirectory(pathToNewDir));

    Files.createDirectory(pathToNewDir);

    assertTrue(Files.isDirectory(pathToNewDir));
}

If you have a directory beneath other directories that you want to create which do not already exist, like parent/child/otherchild, where child does not exist, the above attempt will fail. Make a simple change to createDirectories(..) and the method will take care of that for you:

@Test
public void creatingDirectories_intermediateParentDirectories() throws Exception {
    Path newChainedPath = Paths.get(Utils.pathToResources + "parent-dir/sub-dir");

    Files.deleteIfExists(newChainedPath);

    assertFalse(Files.isDirectory(newChainedPath));

    Files.createDirectories(newChainedPath);

    assertTrue(Files.isDirectory(newChainedPath));
}

We can ask for metadata about files with readAttributes(..):

@Test
public void files_getAttributes() throws Exception {
    Path toExistingFile = Paths.get(Utils.simpleExampleFilePath);

    BasicFileAttributes attributes = Files.readAttributes(toExistingFile, BasicFileAttributes.class);

    assertTrue(attributes.isRegularFile());
    assertEquals(17, attributes.size());
}

We can access all of the Paths immediately beneath a directory with Files.list(..):

@Test
public void visitingDirectories_ex() throws Exception {
    try (Stream<Path> entries = Files.list(Paths.get(Utils.pathToResources))) {
        System.out.println("counting via list");
        long count = entries.peek(System.out::println).count();
        assertTrue(count > 0);
    }
}

The above method will only list the immediate children. If you want to see all the Paths recursively, through each child directory, you'll need to use Files.walk(..):

@Test
public void visitingDirectories_walkSubDirectories() throws Exception {
    try (Stream<Path> entries  = Files.walk(Paths.get(Utils.pathToResources))) {
        System.out.println("counting via walk");
        long count = entries.peek(System.out::println).count();
        assertTrue(count > 0);
    }
}

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