Writing Files - Beginning Java - page 489

// getPrimes() method as in the previous example...

// createFilePath() method as in the previous example...

// Write the array contents to file
private static void writePrimesFile(long[] primes, Path file) {
final int BUFFERSIZE = 100; // Byte buffer size
try (WritableByteChannel channel = Files.newByteChannel(
file, EnumSet.of(WRITE,

CREATE))) {
ByteBuffer buf = ByteBuffer.allocate(BUFFERSIZE);
DoubleBuffer doubleBuf = buf.asDoubleBuffer();
buf.position(8);
CharBuffer charBuf = buf.asCharBuffer();
LongBuffer longBuf = null;
String primeStr = null;

for (long prime : primes) {
primeStr = "prime = " + prime; // Create the

string

doubleBuf.put(0,(double)primeStr.length()); // Store the
string length
charBuf.put(primeStr); // Store the

string

buf.position(2*charBuf.position() + 8); // Position for

3rd buffer
longBuf = buf.asLongBuffer(); // Create the

buffer

longBuf.put(prime); // Store the binary

long value
buf.position(buf.position() + 8); // Set position after

last value
buf.flip(); // and flip

channel.write(buf); // Write the buffer as

before

buf.clear();
doubleBuf.clear();
charBuf.clear();

}
System.out.println("File written is " +
((FileChannel)channel).size() + "

bytes.");
} catch (IOException e) {
e.printStackTrace();

}

}

}

PrimesToFile2.java