Example usage for java.nio.channels FileChannel position

Introduction

In this page you can find the example usage for java.nio.channels FileChannel position.

Prototype

public abstract FileChannel position(long newPosition) throws IOException;

Source Link

Document

Sets this channel's file position.

Usage

From source file:MainClass.java

public static void main(String[] args) throws Exception {
    FileChannel fc = new RandomAccessFile("data.txt", "rw").getChannel();
    fc.position(fc.size());
    fc.write(ByteBuffer.wrap("Some more".getBytes()));
    fc.close();//from w w w .  jav  a  2 s.  c o  m

}

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From source file:GetChannel.java

public static void main(String[] args) throws Exception {
    // Write a file:
    FileChannel fc = new FileOutputStream("data.txt").getChannel();
    fc.write(ByteBuffer.wrap("Some text ".getBytes()));
    fc.close();/*from ww w . jav a 2 s  .  com*/
    // Add to the end of the file:
    fc = new RandomAccessFile("data.txt", "rw").getChannel();
    fc.position(fc.size()); // Move to the end
    fc.write(ByteBuffer.wrap("Some more".getBytes()));
    fc.close();
    // Read the file:
    fc = new FileInputStream("data.txt").getChannel();
    ByteBuffer buff = ByteBuffer.allocate(BSIZE);
    fc.read(buff);
    buff.flip();
    while (buff.hasRemaining())
        System.out.print((char) buff.get());
}

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From source file:Main.java

/**
 * This method handels the write operations for a specified file.
 * //from  ww  w. j  a va 2  s . co m
 * @param file the file to which the data should be written.
 * @param data the data,which should be written to a specified file.
 * @param writeCompleted a flag which indicates, if writing to a file is complete, or
 *            if there data left, which should be append to the end of the
 *            file.
 */
public static void writeFile(File file, byte[] data, boolean writeCompleted) {
    // Writing the encrypted data with header
    try {

        if (fos == null)
            fos = new FileOutputStream(file);

        FileChannel fileChannel = fos.getChannel();

        if (writeStreamPosition != 0L)
            fileChannel.position(writeStreamPosition);

        fos.write(data);
        fos.flush();

        writeStreamPosition = fileChannel.position();

        // reset flags, if file-operation is completed
        if (writeCompleted) {
            fileChannel.close();
            fos.close();
            fos = null;
            writeStreamPosition = 0L;
        }
    } catch (IOException e) {
        e.printStackTrace();
        return;
    }
}

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From source file:Main.java

/**
 * This method handels the reading of data from a specific file.
 * //from  ww w  .  j av a2s . co m
 * @param file the file, to read from.
 * @param blockSize the length of the data-block, which should be read from the specified file.
 * @return the data read from the file.
 */
public static byte[] readFile(File file, long blockSize) {
    FileInputStream fis;
    byte[] fileContent = null;

    try {
        fis = new FileInputStream(file);

        FileChannel fileChannel = fis.getChannel();

        int bytesToRead;
        fileChannel.position(readStreamPosition);

        int dataLen = fis.available();

        // if there is a zero block size specified, read the whole file
        if (blockSize == 0L) {
            bytesToRead = dataLen;
        } else {
            bytesToRead = (int) blockSize;
        }

        fileContent = new byte[bytesToRead];

        // reading the data
        for (int i = 0; i < bytesToRead; i++) {
            fileContent[i] = (byte) fis.read();
        }

        // storing read-position
        readStreamPosition = fileChannel.position();

        fis.close();
        fileChannel.close();

        // zero blockSize indicates, that reading of this file is completed,
        // stream position reset
        if (blockSize == 0L) {
            readStreamPosition = 0L;
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return fileContent;
}

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From source file:com.github.neoio.nio.util.NIOUtils.java

public static void resetFileChannel(FileChannel channel) throws NetIOException {
    try {/*  ww w  .  jav a2  s.c om*/
        channel.position(0);
        channel.truncate(0);
    } catch (IOException e) {
        throw new NetIOException(e);
    }
}

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From source file:com.github.neoio.nio.util.NIOUtils.java

public static void resetFileChannelForReading(FileChannel channel) throws NetIOException {
    try {//from   w ww .jav a2  s  . co  m
        channel.force(true);
        channel.position(0);
    } catch (IOException e) {
        throw new NetIOException(e);
    }
}

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From source file:org.apache.hadoop.hdfs.server.namenode.TestFSEditLogLoader.java

/**
 * Return the length of bytes in the given file after subtracting
 * the trailer of 0xFF (OP_INVALID)s./*from w  w w  .  j  a v  a 2s  . co m*/
 * This seeks to the end of the file and reads chunks backwards until
 * it finds a non-0xFF byte.
 * @throws IOException if the file cannot be read
 */
private static long getNonTrailerLength(File f) throws IOException {
    final int chunkSizeToRead = 256 * 1024;
    FileInputStream fis = new FileInputStream(f);
    try {

        byte buf[] = new byte[chunkSizeToRead];

        FileChannel fc = fis.getChannel();
        long size = fc.size();
        long pos = size - (size % chunkSizeToRead);

        while (pos >= 0) {
            fc.position(pos);

            int readLen = (int) Math.min(size - pos, chunkSizeToRead);
            IOUtils.readFully(fis, buf, 0, readLen);
            for (int i = readLen - 1; i >= 0; i--) {
                if (buf[i] != FSEditLogOpCodes.OP_INVALID.getOpCode()) {
                    return pos + i + 1; // + 1 since we count this byte!
                }
            }

            pos -= chunkSizeToRead;
        }
        return 0;
    } finally {
        fis.close();
    }
}

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From source file:org.cloudata.core.commitlog.pipe.CommitLogFileChannel.java

public static long readLastIndex(FileChannel ch) throws IOException {
    ByteBuffer buf = ByteBuffer.allocate(Long.SIZE / 8);
    long chSize = ch.size();

    if (chSize > 0) {
        ch.position(chSize > (Long.SIZE / 8) ? chSize - (Long.SIZE / 8) : 0);
        ch.read(buf);/*w  w  w . j  a  v  a2s  . c  om*/
        buf.flip();
        return buf.getLong();
    } else {
        return 0;
    }
}

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From source file:jext2.Superblock.java

/**
 * Read superblock using a FileChannel. This is intended for testing and code
 * that just needs the superblock not any file system access.
 *//*  w ww  .j a  v  a2 s . c o  m*/
public static Superblock fromFileChannel(FileChannel chan) throws IoError {

    Superblock sb = new Superblock(-1);
    ByteBuffer buf = ByteBuffer.allocate(Constants.EXT2_MIN_BLOCK_SIZE);
    try {
        chan.position(1024);
        chan.read(buf);
    } catch (IOException e) {
        throw new IoError();
    }
    sb.read(buf);

    Superblock.instance = sb;
    return sb;
}

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From source file:io.undertow.server.handlers.SenderTestCase.java

@BeforeClass
public static void setup() {
    HttpHandler lotsOfSendsHandler = new HttpHandler() {
        @Override//w  w w. ja  va2s. c  om
        public void handleRequest(final HttpServerExchange exchange) throws Exception {
            boolean blocking = exchange.getQueryParameters().get("blocking").getFirst().equals("true");
            if (blocking) {
                if (exchange.isInIoThread()) {
                    exchange.startBlocking();
                    exchange.dispatch(this);
                    return;
                }
            }
            final Sender sender = exchange.getResponseSender();
            class SendClass implements Runnable, IoCallback {

                int sent = 0;

                @Override
                public void run() {
                    sent++;
                    sender.send("a", this);
                }

                @Override
                public void onComplete(final HttpServerExchange exchange, final Sender sender) {
                    if (sent++ == SENDS) {
                        sender.close();
                        return;
                    }
                    sender.send("a", this);
                }

                @Override
                public void onException(final HttpServerExchange exchange, final Sender sender,
                        final IOException exception) {
                    exception.printStackTrace();
                    exchange.endExchange();
                }
            }
            new SendClass().run();
        }
    };
    HttpHandler lotsOfTransferHandler = new HttpHandler() {
        @Override
        public void handleRequest(final HttpServerExchange exchange) throws Exception {

            boolean blocking = exchange.getQueryParameters().get("blocking").getFirst().equals("true");
            if (blocking) {
                if (exchange.isInIoThread()) {
                    exchange.startBlocking();
                    exchange.dispatch(this);
                    return;
                }
            }
            URI uri = SenderTestCase.class.getResource(SenderTestCase.class.getSimpleName() + ".class").toURI();
            Path file = Paths.get(uri);
            final FileChannel channel = FileChannel.open(file, StandardOpenOption.READ);

            exchange.setResponseContentLength(channel.size() * TXS);

            final Sender sender = exchange.getResponseSender();
            class SendClass implements Runnable, IoCallback {

                int sent = 0;

                @Override
                public void run() {
                    sent++;
                    try {
                        channel.position(0);
                    } catch (IOException e) {
                    }
                    sender.transferFrom(channel, this);
                }

                @Override
                public void onComplete(final HttpServerExchange exchange, final Sender sender) {
                    if (sent++ == TXS) {
                        sender.close();
                        return;
                    }
                    try {
                        channel.position(0);
                    } catch (IOException e) {
                    }
                    sender.transferFrom(channel, this);
                }

                @Override
                public void onException(final HttpServerExchange exchange, final Sender sender,
                        final IOException exception) {
                    exception.printStackTrace();
                    exchange.endExchange();
                }
            }
            new SendClass().run();
        }
    };

    final HttpHandler fixedLengthSender = new HttpHandler() {
        @Override
        public void handleRequest(final HttpServerExchange exchange) throws Exception {
            exchange.getResponseSender().send(HELLO_WORLD);
        }
    };

    PathHandler handler = new PathHandler().addPrefixPath("/lots", lotsOfSendsHandler)
            .addPrefixPath("/fixed", fixedLengthSender).addPrefixPath("/transfer", lotsOfTransferHandler);
    DefaultServer.setRootHandler(handler);
}

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