You are intend to write data into one file. So if you try to lock the whole file, it'd better to use a single thread to do this job. Although you spawn 20 threads, but there is only one of them is running every time you call the method, the others are just waiting for the lock.
I recommend you use RandomAccessFile
to write data to your file. Then each thread can write some unique data into to the file without locking the whole file.
Some demo code as following
try {
final RandomAccessFile file = new RandomAccessFile("/path/to/your/result.txt", "rw");
final int numberOfThread = 20;
final int bufferSize = 512;
ExecutorService pool = Executors.newFixedThreadPool(numberOfThread);
final AtomicInteger byteCounter = new AtomicInteger(0);
final byte[] yourText = "Your data".getBytes();
for (int i = 0; i < yourText.length; i++) {
pool.submit(new Runnable() {
@Override
public void run() {
int start = byteCounter.getAndAdd(bufferSize);
int chunkSize = bufferSize;
if (start + bufferSize > yourText.length) {
chunkSize = yourText.length - start;
}
byte[] chunkData = new byte[chunkSize];
System.arraycopy(yourText, start, chunkData, 0, chunkSize);
try {
file.write(chunkData);
} catch (IOException e) {
//exception handle
}
}
});
}
file.close();
} catch (Exception e) {
//clean up
}