http://poi.apache.org/: Apache POI - Java API To Access Microsoft Format Files (Apache Software Foundation) 
/* ====================================================================
   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
==================================================================== */

package org.apache.poi.util;

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;
import java.util.zip.CRC32;
import java.util.zip.Checksum;

import org.apache.poi.EmptyFileException;
import org.apache.poi.POIDocument;
import org.apache.poi.ss.usermodel.Workbook;

public final class IOUtils {
    private static final POILogger logger = POILogFactory.getLogger( IOUtils.class );

    
The default buffer size to use for the skip() methods.

/**
     * The default buffer size to use for the skip() methods.
     */
    private static final int SKIP_BUFFER_SIZE = 2048;
    private static int BYTE_ARRAY_MAX_OVERRIDE = -1;
    private static byte[] SKIP_BYTE_BUFFER;

    private IOUtils() {
        // no instances of this class
    }

    
If this value is set to > 0, safelyAllocate(long, int) will ignore the maximum record length parameter. This is designed to allow users to bypass the hard-coded maximum record lengths if they are willing to accept the risk of an OutOfMemoryException. 
Params:
  • maxOverride – The number of bytes that should be possible to be allocated in one step.
Since:4.0.0
/**
     * If this value is set to > 0, {@link #safelyAllocate(long, int)} will ignore the
     * maximum record length parameter.  This is designed to allow users to bypass
     * the hard-coded maximum record lengths if they are willing to accept the risk
     * of an OutOfMemoryException.
     *
     * @param maxOverride The number of bytes that should be possible to be allocated in one step.
     * @since 4.0.0
     */
    @SuppressWarnings("unused")
    public static void setByteArrayMaxOverride(int maxOverride) {
        BYTE_ARRAY_MAX_OVERRIDE = maxOverride;
    }

    
Peeks at the first 8 bytes of the stream. Returns those bytes, but
 with the stream unaffected. Requires a stream that supports mark/reset,
 or a PushbackInputStream. If the stream has >0 but <8 bytes, 
 remaining bytes will be zero.

Throws:
  • EmptyFileException – if the stream is empty
/**
     * Peeks at the first 8 bytes of the stream. Returns those bytes, but
     *  with the stream unaffected. Requires a stream that supports mark/reset,
     *  or a PushbackInputStream. If the stream has &gt;0 but &lt;8 bytes, 
     *  remaining bytes will be zero.
     * @throws EmptyFileException if the stream is empty
     */
    public static byte[] peekFirst8Bytes(InputStream stream) throws IOException, EmptyFileException {
        return peekFirstNBytes(stream, 8);
    }

    
Peeks at the first N bytes of the stream. Returns those bytes, but
 with the stream unaffected. Requires a stream that supports mark/reset,
 or a PushbackInputStream. If the stream has >0 but <N bytes,
 remaining bytes will be zero.

Throws:
  • EmptyFileException – if the stream is empty
/**
     * Peeks at the first N bytes of the stream. Returns those bytes, but
     *  with the stream unaffected. Requires a stream that supports mark/reset,
     *  or a PushbackInputStream. If the stream has &gt;0 but &lt;N bytes,
     *  remaining bytes will be zero.
     * @throws EmptyFileException if the stream is empty
     */
    public static byte[] peekFirstNBytes(InputStream stream, int limit) throws IOException, EmptyFileException {
        stream.mark(limit);
        ByteArrayOutputStream bos = new ByteArrayOutputStream(limit);
        copy(new BoundedInputStream(stream, limit), bos);

        int readBytes = bos.size();
        if (readBytes == 0) {
            throw new EmptyFileException();
        }

        if (readBytes < limit) {
            bos.write(new byte[limit-readBytes]);
        }
        byte[] peekedBytes = bos.toByteArray();
        if(stream instanceof PushbackInputStream) {
            PushbackInputStream pin = (PushbackInputStream)stream;
            pin.unread(peekedBytes, 0, readBytes);
        } else {
            stream.reset();
        }

        return peekedBytes;
    }

    
Reads all the data from the input stream, and returns the bytes read.

Params:
  • stream – The byte stream of data to read.
Throws:
  • IOException – If reading data fails or EOF is encountered too early for the given length.
Returns:A byte array with the read bytes.
/**
     * Reads all the data from the input stream, and returns the bytes read.
     *
     * @param stream The byte stream of data to read.
     * @return A byte array with the read bytes.
     * @throws IOException If reading data fails or EOF is encountered too early for the given length.
     */
    public static byte[] toByteArray(InputStream stream) throws IOException {
        return toByteArray(stream, Integer.MAX_VALUE);
    }

    
Reads up to length bytes from the input stream, and returns the bytes read. 
Params:
  • stream – The byte stream of data to read.
  • length – The maximum length to read, use Integer.MAX_VALUE to read the stream
              until EOF.
Throws:
  • IOException – If reading data fails or EOF is encountered too early for the given length.
Returns:A byte array with the read bytes.
/**
     * Reads up to {@code length} bytes from the input stream, and returns the bytes read.
     *
     * @param stream The byte stream of data to read.
     * @param length The maximum length to read, use Integer.MAX_VALUE to read the stream
     *               until EOF.
     * @return A byte array with the read bytes.
     * @throws IOException If reading data fails or EOF is encountered too early for the given length.
     */
    public static byte[] toByteArray(InputStream stream, final int length) throws IOException {
        return toByteArray(stream, length, Integer.MAX_VALUE);
    }


    
Reads up to length bytes from the input stream, and returns the bytes read. 
Params:
  • stream – The byte stream of data to read.
  • length – The maximum length to read, use Integer.MAX_VALUE to read the stream until EOF
  • maxLength – if the input is equal to/longer than maxLength bytes, then throw an IOException complaining about the length. use Integer.MAX_VALUE to disable the check
Throws:
  • IOException – If reading data fails or EOF is encountered too early for the given length.
Returns:A byte array with the read bytes.
/**
     * Reads up to {@code length} bytes from the input stream, and returns the bytes read.
     *
     * @param stream The byte stream of data to read.
     * @param length The maximum length to read, use {@link Integer#MAX_VALUE} to read the stream
     *               until EOF
     * @param maxLength if the input is equal to/longer than {@code maxLength} bytes,
 *                   then throw an {@link IOException} complaining about the length.
*                    use {@link Integer#MAX_VALUE} to disable the check
     * @return A byte array with the read bytes.
     * @throws IOException If reading data fails or EOF is encountered too early for the given length.
     */
    public static byte[] toByteArray(InputStream stream, final long length, final int maxLength) throws IOException {
        if (length < 0L || maxLength < 0L) {
            throw new RecordFormatException("Can't allocate an array of length < 0");
        }
        if (length > (long)Integer.MAX_VALUE) {
            throw new RecordFormatException("Can't allocate an array > "+Integer.MAX_VALUE);
        }
        checkLength(length, maxLength);

        final int len = Math.min((int)length, maxLength);
        ByteArrayOutputStream baos = new ByteArrayOutputStream(len == Integer.MAX_VALUE ? 4096 : len);

        byte[] buffer = new byte[4096];
        int totalBytes = 0, readBytes;
        do {
            readBytes = stream.read(buffer, 0, Math.min(buffer.length, len-totalBytes));
            totalBytes += Math.max(readBytes,0);
            if (readBytes > 0) {
                baos.write(buffer, 0, readBytes);
            }
        } while (totalBytes < len && readBytes > -1);

        if (maxLength != Integer.MAX_VALUE && totalBytes == maxLength) {
            throw new IOException("MaxLength ("+maxLength+") reached - stream seems to be invalid.");
        }

        if (len != Integer.MAX_VALUE && totalBytes < len) {
            throw new EOFException("unexpected EOF - expected len: "+len+" - actual len: "+totalBytes);
        }

        return baos.toByteArray();
    }

    private static void checkLength(long length, int maxLength) {
        if (BYTE_ARRAY_MAX_OVERRIDE > 0) {
            if (length > BYTE_ARRAY_MAX_OVERRIDE) {
                throwRFE(length, BYTE_ARRAY_MAX_OVERRIDE);
            }
        } else if (length > maxLength) {
            throwRFE(length, maxLength);
        }
    }


    
Returns an array (that shouldn't be written to!) of the
 ByteBuffer. Will be of the requested length, or possibly
 longer if that's easier.

/**
     * Returns an array (that shouldn't be written to!) of the
     *  ByteBuffer. Will be of the requested length, or possibly
     *  longer if that's easier.
     */
    public static byte[] toByteArray(ByteBuffer buffer, int length) {
        if(buffer.hasArray() && buffer.arrayOffset() == 0) {
            // The backing array should work out fine for us
            return buffer.array();
        }

        byte[] data = new byte[length];
        buffer.get(data);
        return data;
    }

    
Helper method, just calls readFully(in, b, 0, b.length)

/**
     * Helper method, just calls <tt>readFully(in, b, 0, b.length)</tt>
     */
    public static int readFully(InputStream in, byte[] b) throws IOException {
        return readFully(in, b, 0, b.length);
    }

    
Same as the normal InputStream.read(byte[], int, int), but tries to ensure that the entire len number of bytes is read.


If the end of file is reached before any bytes are read, returns -1. If
the end of the file is reached after some bytes are read, returns the
number of bytes read. If the end of the file isn't reached before len
bytes have been read, will return len bytes.


Params:
  • in – the stream from which the data is read.
  • b – the buffer into which the data is read.
  • off – the start offset in array b at which the data is written.
  • len – the maximum number of bytes to read.
/**
     * <p>Same as the normal {@link InputStream#read(byte[], int, int)}, but tries to ensure
     * that the entire len number of bytes is read.</p>
     * 
     * <p>If the end of file is reached before any bytes are read, returns <tt>-1</tt>. If
     * the end of the file is reached after some bytes are read, returns the
     * number of bytes read. If the end of the file isn't reached before <tt>len</tt>
     * bytes have been read, will return <tt>len</tt> bytes.</p>
     * 
     * @param in the stream from which the data is read.
     * @param b the buffer into which the data is read.
     * @param off the start offset in array <tt>b</tt> at which the data is written.
     * @param len the maximum number of bytes to read.
     */
    public static int readFully(InputStream in, byte[] b, int off, int len) throws IOException {
        int total = 0;
        while (true) {
            int got = in.read(b, off + total, len - total);
            if (got < 0) {
                return (total == 0) ? -1 : total;
            }
            total += got;
            if (total == len) {
                return total;
            }
        }
    }

    
Same as the normal channel.read(b), but tries to ensure
that the buffer is filled completely if possible, i.e. b.remaining()
returns 0.


If the end of file is reached before any bytes are read, returns -1. If
the end of the file is reached after some bytes are read, returns the
number of bytes read. If the end of the file isn't reached before the
buffer has no more remaining capacity, will return the number of bytes
that were read.

/**
     * Same as the normal <tt>channel.read(b)</tt>, but tries to ensure
     * that the buffer is filled completely if possible, i.e. b.remaining()
     * returns 0.
     * <p>
     * If the end of file is reached before any bytes are read, returns -1. If
     * the end of the file is reached after some bytes are read, returns the
     * number of bytes read. If the end of the file isn't reached before the
     * buffer has no more remaining capacity, will return the number of bytes
     * that were read.
     */
    public static int readFully(ReadableByteChannel channel, ByteBuffer b) throws IOException {
        int total = 0;
        while (true) {
            int got = channel.read(b);
            if (got < 0) {
                return (total == 0) ? -1 : total;
            }
            total += got;
            if (total == b.capacity() || b.position() == b.capacity()) {
                return total;
            }
        }
    }

    
Write a POI Document (Workbook, SlideShow, etc) to an output stream and close the output stream. This will attempt to close the output stream at the end even if there was a problem writing the document to the stream. If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead. This function exists for Java 6 code. 
Params:
  • doc –  a writeable document to write to the output stream
  • out –  the output stream that the document is written to
Throws:
Deprecated:since 4.0, use try-with-resources, will be removed in 4.2
/**
     * Write a POI Document ({@link org.apache.poi.ss.usermodel.Workbook}, {@link org.apache.poi.sl.usermodel.SlideShow}, etc) to an output stream and close the output stream.
     * This will attempt to close the output stream at the end even if there was a problem writing the document to the stream.
     *
     * If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead.
     * This function exists for Java 6 code.
     *
     * @param doc  a writeable document to write to the output stream
     * @param out  the output stream that the document is written to
     * @throws IOException thrown on errors writing to the stream
     *
     * @deprecated since 4.0, use try-with-resources, will be removed in 4.2
     */
    @Deprecated
    @Removal(version="4.2")
    public static void write(POIDocument doc, OutputStream out) throws IOException {
        try {
            doc.write(out);
        } finally {
            closeQuietly(out);
        }
    }

    
Write a (Workbook) to an output stream and close the output stream. This will attempt to close the output stream at the end even if there was a problem writing the document to the stream. If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead. This function exists for Java 6 code. 
Params:
  • doc –  a writeable document to write to the output stream
  • out –  the output stream that the document is written to
Throws:
Deprecated:since 4.0, use try-with-resources, will be removed in 4.2
/**
     * Write a ({@link org.apache.poi.ss.usermodel.Workbook}) to an output stream and close the output stream.
     * This will attempt to close the output stream at the end even if there was a problem writing the document to the stream.
     *
     * If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead.
     * This function exists for Java 6 code.
     *
     * @param doc  a writeable document to write to the output stream
     * @param out  the output stream that the document is written to
     * @throws IOException thrown on errors writing to the stream
     *
     * @deprecated since 4.0, use try-with-resources, will be removed in 4.2
     */
    @Deprecated
    @Removal(version="4.2")
    public static void write(Workbook doc, OutputStream out) throws IOException {
        try {
            doc.write(out);
        } finally {
            closeQuietly(out);
        }
    }

    
Write a POI Document (Workbook, SlideShow, etc) to an output stream and close the output stream. This will attempt to close the output stream at the end even if there was a problem writing the document to the stream. This will also attempt to close the document, even if an error occurred while writing the document or closing the output stream. If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead. This function exists for Java 6 code. 
Params:
  • doc –  a writeable and closeable document to write to the output stream, then close
  • out –  the output stream that the document is written to
Throws:
Deprecated:since 4.0, use try-with-resources, will be removed in 4.2
/**
     * Write a POI Document ({@link org.apache.poi.ss.usermodel.Workbook}, {@link org.apache.poi.sl.usermodel.SlideShow}, etc) to an output stream and close the output stream.
     * This will attempt to close the output stream at the end even if there was a problem writing the document to the stream.
     * This will also attempt to close the document, even if an error occurred while writing the document or closing the output stream.
     *
     * If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead.
     * This function exists for Java 6 code.
     *
     * @param doc  a writeable and closeable document to write to the output stream, then close
     * @param out  the output stream that the document is written to
     * @throws IOException thrown on errors writing to the stream
     *
     * @deprecated since 4.0, use try-with-resources, will be removed in 4.2
     */
    @Deprecated
    @Removal(version="4.2")
    public static void writeAndClose(POIDocument doc, OutputStream out) throws IOException {
        try {
            write(doc, out);
        } finally {
            closeQuietly(doc);
        }
    }

    
Like writeAndClose(POIDocument, OutputStream), but for writing to a File instead of an OutputStream. This will attempt to close the document, even if an error occurred while writing the document. If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead. This function exists for Java 6 code. 
Params:
  • doc –  a writeable and closeable document to write to the output file, then close
  • out –  the output file that the document is written to
Throws:
Deprecated:since 4.0, use try-with-resources, will be removed in 4.2
/**
     * Like {@link #writeAndClose(POIDocument, OutputStream)}, but for writing to a File instead of an OutputStream.
     * This will attempt to close the document, even if an error occurred while writing the document.
     *
     * If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead.
     * This function exists for Java 6 code.
     *
     * @param doc  a writeable and closeable document to write to the output file, then close
     * @param out  the output file that the document is written to
     * @throws IOException thrown on errors writing to the stream
     *
     * @deprecated since 4.0, use try-with-resources, will be removed in 4.2
     */
    @Deprecated
    @Removal(version="4.2")
    public static void writeAndClose(POIDocument doc, File out) throws IOException {
        try {
            doc.write(out);
        } finally {
            closeQuietly(doc);
        }
    }

    
Like writeAndClose(POIDocument, File), but for writing a POI Document in place (to the same file that it was opened from). This will attempt to close the document, even if an error occurred while writing the document. If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead. This function exists for Java 6 code. 
Params:
  • doc –  a writeable document to write in-place
Throws:
Deprecated:since 4.0, use try-with-resources, will be removed in 4.2
/**
     * Like {@link #writeAndClose(POIDocument, File)}, but for writing a POI Document in place (to the same file that it was opened from).
     * This will attempt to close the document, even if an error occurred while writing the document.
     *
     * If you are using Java 7 or higher, you may prefer to use a try-with-resources statement instead.
     * This function exists for Java 6 code.
     *
     * @param doc  a writeable document to write in-place
     * @throws IOException thrown on errors writing to the file
     *
     * @deprecated since 4.0, use try-with-resources, will be removed in 4.2
     */
    @Deprecated
    @Removal(version="4.2")
    public static void writeAndClose(POIDocument doc) throws IOException {
        try {
            doc.write();
        } finally {
            closeQuietly(doc);
        }
    }

    // Since the Workbook interface doesn't derive from POIDocument
    // We'll likely need one of these for each document container interface
    
Deprecated:since 4.0, use try-with-resources, will be removed in 4.2
/**
     *
     * @deprecated since 4.0, use try-with-resources, will be removed in 4.2
     */
    @Deprecated
    @Removal(version="4.2")
    public static void writeAndClose(Workbook doc, OutputStream out) throws IOException {
        try {
            doc.write(out);
        } finally {
            closeQuietly(doc);
        }
    }

    
Copies all the data from the given InputStream to the OutputStream. It
leaves both streams open, so you will still need to close them once done.

Params:
Throws:
Returns:the amount of bytes copied
/**
     * Copies all the data from the given InputStream to the OutputStream. It
     * leaves both streams open, so you will still need to close them once done.
     *
     * @param inp The {@link InputStream} which provides the data
     * @param out The {@link OutputStream} to write the data to
     * @return the amount of bytes copied
     *
     * @throws IOException If copying the data fails.
     */
    public static long copy(InputStream inp, OutputStream out) throws IOException {
        return copy(inp, out, -1);
    }

    
Copies all the data from the given InputStream to the OutputStream. It
leaves both streams open, so you will still need to close them once done.

Params:
  • inp – The InputStream which provides the data
  • out – The OutputStream to write the data to
  • limit – limit the copied bytes - use -1 for no limit
Throws:
Returns:the amount of bytes copied
/**
     * Copies all the data from the given InputStream to the OutputStream. It
     * leaves both streams open, so you will still need to close them once done.
     *
     * @param inp The {@link InputStream} which provides the data
     * @param out The {@link OutputStream} to write the data to
     * @param limit limit the copied bytes - use {@code -1} for no limit
     * @return the amount of bytes copied
     *
     * @throws IOException If copying the data fails.
     */
    public static long copy(InputStream inp, OutputStream out, long limit) throws IOException {
        final byte[] buff = new byte[4096];
        long totalCount = 0;
        int readBytes = -1;
        do {
            int todoBytes = (int)((limit < 0) ? buff.length : Math.min(limit-totalCount, buff.length));
            if (todoBytes > 0) {
                readBytes = inp.read(buff, 0, todoBytes);
                if (readBytes > 0) {
                    out.write(buff, 0, readBytes);
                    totalCount += readBytes;
                }
            }
        } while (readBytes >= 0 && (limit == -1 || totalCount < limit));

        return totalCount;
    }

    
Copy the contents of the stream to a new file.

Params:
  • srcStream – The InputStream which provides the data
  • destFile – The file where the data should be stored
Throws:
  • IOException – If the target directory does not exist and cannot be created
     or if copying the data fails.
Returns:the amount of bytes copied
/**
     * Copy the contents of the stream to a new file.
     *
     * @param srcStream The {@link InputStream} which provides the data
     * @param destFile The file where the data should be stored
     * @return the amount of bytes copied
     *
     * @throws IOException If the target directory does not exist and cannot be created
     *      or if copying the data fails.
     */
    public static long copy(InputStream srcStream, File destFile) throws IOException {
        File destDirectory = destFile.getParentFile();
        if (!(destDirectory.exists() || destDirectory.mkdirs())) {
            throw new RuntimeException("Can't create destination directory: "+destDirectory);
        }
        try (OutputStream destStream = new FileOutputStream(destFile)) {
            return IOUtils.copy(srcStream, destStream);
        }
    }

    
Calculate checksum on input data

/**
     * Calculate checksum on input data
     */
    public static long calculateChecksum(byte[] data) {
        Checksum sum = new CRC32();
        sum.update(data, 0, data.length);
        return sum.getValue();
    }

    
Calculate checksum on all the data read from input stream. This should be more efficient than the equivalent code IOUtils.calculateChecksum(IOUtils.toByteArray(stream)) 
/**
     * Calculate checksum on all the data read from input stream.
     *
     * This should be more efficient than the equivalent code
     * {@code IOUtils.calculateChecksum(IOUtils.toByteArray(stream))}
     */
    public static long calculateChecksum(InputStream stream) throws IOException {
        Checksum sum = new CRC32();

        byte[] buf = new byte[4096];
        int count;
        while ((count = stream.read(buf)) != -1) {
            if (count > 0) {
                sum.update(buf, 0, count);
            }
        }
        return sum.getValue();
    }
    
    
    
Quietly (no exceptions) close Closable resource. In case of error it will be printed to IOUtils class logger. 
Params:
  • closeable – 
           resource to close
/**
     * Quietly (no exceptions) close Closable resource. In case of error it will
     * be printed to {@link IOUtils} class logger.
     * 
     * @param closeable
     *            resource to close
     */
    public static void closeQuietly( final Closeable closeable ) {
        // no need to log a NullPointerException here
        if(closeable == null) {
            return;
        }

        try {
            closeable.close();
        } catch ( Exception exc ) {
            logger.log( POILogger.ERROR, "Unable to close resource: " + exc,
                    exc );
        }
    }


    
Skips bytes from an input byte stream. This implementation guarantees that it will read as many bytes as possible before giving up; this may not always be the case for skip() implementations in subclasses of InputStream. 
 Note that the implementation uses InputStream.read(byte[], int, int) rather than delegating to InputStream.skip(long). This means that the method may be considerably less efficient than using the actual skip implementation, this is done to guarantee that the correct number of bytes are skipped. 


 This mimics POI's readFully(InputStream, byte[]). If the end of file is reached before any bytes are read, returns -1. If
the end of the file is reached after some bytes are read, returns the
number of bytes read. If the end of the file isn't reached before len
bytes have been read, will return len bytes.





Copied nearly verbatim from commons-io 41a3e9c



Params:
  • input – byte stream to skip
  • toSkip – number of bytes to skip.
Throws:
See Also:
Returns:number of bytes actually skipped.
/**
     * Skips bytes from an input byte stream.
     * This implementation guarantees that it will read as many bytes
     * as possible before giving up; this may not always be the case for
     * skip() implementations in subclasses of {@link InputStream}.
     * <p>
     * Note that the implementation uses {@link InputStream#read(byte[], int, int)} rather
     * than delegating to {@link InputStream#skip(long)}.
     * This means that the method may be considerably less efficient than using the actual skip implementation,
     * this is done to guarantee that the correct number of bytes are skipped.
     * </p>
     * <p>
     * This mimics POI's {@link #readFully(InputStream, byte[])}.
     * If the end of file is reached before any bytes are read, returns <tt>-1</tt>. If
     * the end of the file is reached after some bytes are read, returns the
     * number of bytes read. If the end of the file isn't reached before <tt>len</tt>
     * bytes have been read, will return <tt>len</tt> bytes.</p>

     * </p>
     * <p>
     * Copied nearly verbatim from commons-io 41a3e9c
     * </p>
     *
     * @param input byte stream to skip
     * @param toSkip number of bytes to skip.
     * @return number of bytes actually skipped.
     * @throws IOException              if there is a problem reading the file
     * @throws IllegalArgumentException if toSkip is negative
     * @see InputStream#skip(long)
     *
     */
    public static long skipFully(final InputStream input, final long toSkip) throws IOException {
        if (toSkip < 0) {
            throw new IllegalArgumentException("Skip count must be non-negative, actual: " + toSkip);
        }
        if (toSkip == 0) {
            return 0L;
        }
        /*
         * N.B. no need to synchronize this because: - we don't care if the buffer is created multiple times (the data
         * is ignored) - we always use the same size buffer, so if it it is recreated it will still be OK (if the buffer
         * size were variable, we would need to synch. to ensure some other thread did not create a smaller one)
         */
        if (SKIP_BYTE_BUFFER == null) {
            SKIP_BYTE_BUFFER = new byte[SKIP_BUFFER_SIZE];
        }
        long remain = toSkip;
        while (remain > 0) {
            // See https://issues.apache.org/jira/browse/IO-203 for why we use read() rather than delegating to skip()
            final long n = input.read(SKIP_BYTE_BUFFER, 0, (int) Math.min(remain, SKIP_BUFFER_SIZE));
            if (n < 0) { // EOF
                break;
            }
            remain -= n;
        }
        if (toSkip == remain) {
            return -1L;
        }
        return toSkip - remain;
    }

    public static byte[] safelyAllocate(long length, int maxLength) {
        if (length < 0L) {
            throw new RecordFormatException("Can't allocate an array of length < 0, but had " + length + " and " + maxLength);
        }
        if (length > (long)Integer.MAX_VALUE) {
            throw new RecordFormatException("Can't allocate an array > "+Integer.MAX_VALUE);
        }
        checkLength(length, maxLength);
        return new byte[(int)length];
    }

    
Simple utility function to check that you haven't hit EOF
when reading a byte.

Params:
  • is – inputstream to read
Throws:
Returns:byte read, unless
/**
     * Simple utility function to check that you haven't hit EOF
     * when reading a byte.
     *
     * @param is inputstream to read
     * @return byte read, unless
     * @throws IOException on IOException or EOF if -1 is read
     */
    public static int readByte(InputStream is) throws IOException {
        int b = is.read();
        if (b == -1) {
            throw new EOFException();
        }
        return b;
    }

    private static void throwRFE(long length, int maxLength) {
        throw new RecordFormatException("Tried to allocate an array of length "+length +
                ", but "+ maxLength+" is the maximum for this record type.\n" +
                "If the file is not corrupt, please open an issue on bugzilla to request \n" +
                "increasing the maximum allowable size for this record type.\n"+
                "As a temporary workaround, consider setting a higher override value with " +
                "IOUtils.setByteArrayMaxOverride()");

    }
}