Accessing Files and Directories - Beginning Java - page 424

CHARACTER
SEQUENCE

EFFECT

Specifies a set of subpatterns that can be matched where the subpatterns are separated by commas. For
example, {exe, txt} matches either exe or txt .

{}

All other characters not in Table 9-5 match themselves. Thus to see only .exe files from a directory
stream, you use the glob "*.exe" . To see only .exe and .txt files, you could use "*.{exe,txt}" . The
glob "*.???" matches any file with a three-character extension.

CLOSING A STREAM
In the code fragment in the previous section, there is no provision for calling the close() method for the
DirectoryStream<Path> object and there really should be. In general, you should not call the close()
method for a stream in a try block that has other stream operations that also throw exceptions because if
such exceptions are thrown, the close() method call may be circumvented. Because the close() method
itself can throw an exception of type IOException that must be caught there is the potential for rather messy
code to take care of all eventualities. A new version of the try block was introduced in Java 7 called a try
block-with-resources that makes it very easy to ensure that a stream is closed when you are done with it.
The try block with resources language facility provides the capability for automatically closing streams
at the end of executing the code in the try block, regardless of how execution of the block terminates. This
works with object of any class type that implements the AutoCloseable interface.
To call the close() method automatically, you must create the stream objects between parentheses that
immediately following the try keyword. If you need to create multiple stream objects, just separate the
statements between the parentheses with semicolons. Stream objects that you create here are implicitly fi-
nal so they cannot be changed within the try block. Here's a revised version of the fragment from the pre-
vious section using a try block with resources:
Path currentPath = Paths.get(System.getProperty("user.dir"));
try (DirectoryStream<Path> paths = Files.newDirectoryStream(currentPath)){
for(Path path : paths) {
System.out.println(path.getFileName());

}
} catch(NotDirectoryException e) {
System.err.println(currentPath + " is not a directory." + e);
} catch(IOException e) {
System.err.println("I/O error: " + e);

}

The close() method for paths is called after the try block code completes, whether or not an exception
is thrown from within the block. The close() method is not called if paths is null .
Let's try this out in an example.

TRY IT OUT: Listing the Contents of a Directory
In this example, we list the entire contents of a directory and then use a filter to select particular entries.