Reading Files - Beginning Java - page 501

Path file = Paths.get(System.getProperty("user.home")).
resolve("Beginning Java Stuff").resolve("MyFile.txt");
// Make sure we have a directory...
try(BufferedInputStream in =
new BufferedInputStream(Files.newInputStream(file))){
// read the file...
} catch(IOException e) {
e.printStackTrace();
}
The first argument to the newInputStream() method is the path to the file. You can supply optional ar-
guments following the first to specify the open options to be in effect when the file is opened. These are the
options from the java.nio.file.StandardOpenOption enumeration that you saw in the previous chapter.
The newInputStream() method assumes the READ open option if you do not specify any options. The meth-
od can throw the following exceptions:
• IllegalArgumentException if you specify an invalid combination of options
• UnsupportedOperationException if you specify an option that is not supported
• IOException if an I/O error occurs while opening the file
• SecurityException if the installed security manager determines that you are not permitted to
read the file
Wrapping the InputStream object that the method returns in a java.io.BufferedInputStream object
provides more efficient read operations. The stream has an internal buffer of a default size that is automat-
ically filled by reading from the file as you read from the buffered stream. You can create a BufferedIn-
putStream object with a buffer of a given size by specifying a second argument to the constructor of type
int that determines the capacity of the stream buffer in bytes.
Buffered Stream Read Operations
You have two methods that read from a buffered input stream:
• read() reads a single byte from the stream buffer and returns it as a value of type int . If the end-
of-file (EOF) is reached, the method returns −1.
• read(byte[] bytes, int offset, int length) reads up to length bytes from the stream and
stores them in the bytes array starting at index position offset . Less than length bytes are read
if there are fewer than this number of bytes available up to end-of-file. The method returns the ac-
tual number of bytes read as type int or −1 if no bytes were read because EOF was reached. The
method throws a NullPointerException if the first argument is null and an IndexOutOfBound-
sException if offset or length are invalid or if the bytes.length-offset is less than length .
Both methods throw an IOException if the stream has been closed or if an I/O error occurs.
You can skip over a given number of bytes in the file by calling the skip() method for the stream object.
You specify the number of bytes that you want to skip as an argument of type long . The method returns the
actual number of bytes skipped as a long value. The method throws an IOException if an I/O error occurs
or if the underlying stream does not support seek, which means when mark() and reset() operations are
not supported.