https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 com.google.common.io;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndex;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.math.IntMath;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInput;
import java.io.DataInputStream;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Deque;


Provides utility methods for working with byte arrays and I/O streams.

Author:Chris Nokleberg, Colin Decker
Since:1.0
/**
 * Provides utility methods for working with byte arrays and I/O streams.
 *
 * @author Chris Nokleberg
 * @author Colin Decker
 * @since 1.0
 */
@Beta
@GwtIncompatible
public final class ByteStreams {

  private static final int BUFFER_SIZE = 8192;

  
Creates a new byte array for buffering reads or writes. 
/** Creates a new byte array for buffering reads or writes. */
  static byte[] createBuffer() {
    return new byte[BUFFER_SIZE];
  }

  
There are three methods to implement FileChannel.transferTo(long, long, WritableByteChannel): 
    
  
  1. Use sendfile(2) or equivalent. Requires that both the input channel and the output
      channel have their own file descriptors. Generally this only happens when both channels
      are files or sockets. This performs zero copies - the bytes never enter userspace.
  
  2. Use mmap(2) or equivalent. Requires that either the input channel or the output channel
      have file descriptors. Bytes are copied from the file into a kernel buffer, then directly
      into the other buffer (userspace). Note that if the file is very large, a naive
      implementation will effectively put the whole file in memory. On many systems with paging
      and virtual memory, this is not a problem - because it is mapped read-only, the kernel
      can always page it to disk "for free". However, on systems where killing processes
      happens all the time in normal conditions (i.e., android) the OS must make a tradeoff
      between paging memory and killing other processes - so allocating a gigantic buffer and
      then sequentially accessing it could result in other processes dying. This is solvable
      via madvise(2), but that obviously doesn't exist in java.
  
  3. Ordinary copy. Kernel copies bytes into a kernel buffer, from a kernel buffer into a
      userspace buffer (byte[] or ByteBuffer), then copies them from that buffer into the
      destination channel.


This value is intended to be large enough to make the overhead of system calls negligible,
without being so large that it causes problems for systems with atypical memory management if
approaches 2 or 3 are used.

/**
   * There are three methods to implement {@link FileChannel#transferTo(long, long,
   * WritableByteChannel)}:
   *
   * <ol>
   *   <li>Use sendfile(2) or equivalent. Requires that both the input channel and the output
   *       channel have their own file descriptors. Generally this only happens when both channels
   *       are files or sockets. This performs zero copies - the bytes never enter userspace.
   *   <li>Use mmap(2) or equivalent. Requires that either the input channel or the output channel
   *       have file descriptors. Bytes are copied from the file into a kernel buffer, then directly
   *       into the other buffer (userspace). Note that if the file is very large, a naive
   *       implementation will effectively put the whole file in memory. On many systems with paging
   *       and virtual memory, this is not a problem - because it is mapped read-only, the kernel
   *       can always page it to disk "for free". However, on systems where killing processes
   *       happens all the time in normal conditions (i.e., android) the OS must make a tradeoff
   *       between paging memory and killing other processes - so allocating a gigantic buffer and
   *       then sequentially accessing it could result in other processes dying. This is solvable
   *       via madvise(2), but that obviously doesn't exist in java.
   *   <li>Ordinary copy. Kernel copies bytes into a kernel buffer, from a kernel buffer into a
   *       userspace buffer (byte[] or ByteBuffer), then copies them from that buffer into the
   *       destination channel.
   * </ol>
   *
   * This value is intended to be large enough to make the overhead of system calls negligible,
   * without being so large that it causes problems for systems with atypical memory management if
   * approaches 2 or 3 are used.
   */
  private static final int ZERO_COPY_CHUNK_SIZE = 512 * 1024;

  private ByteStreams() {}

  
Copies all bytes from the input stream to the output stream. Does not close or flush either
stream.

Params:
  • from – the input stream to read from
  • to – the output stream to write to
Throws:
Returns:the number of bytes copied
/**
   * Copies all bytes from the input stream to the output stream. Does not close or flush either
   * stream.
   *
   * @param from the input stream to read from
   * @param to the output stream to write to
   * @return the number of bytes copied
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue
  public static long copy(InputStream from, OutputStream to) throws IOException {
    checkNotNull(from);
    checkNotNull(to);
    byte[] buf = createBuffer();
    long total = 0;
    while (true) {
      int r = from.read(buf);
      if (r == -1) {
        break;
      }
      to.write(buf, 0, r);
      total += r;
    }
    return total;
  }

  
Copies all bytes from the readable channel to the writable channel. Does not close or flush
either channel.

Params:
  • from – the readable channel to read from
  • to – the writable channel to write to
Throws:
Returns:the number of bytes copied
/**
   * Copies all bytes from the readable channel to the writable channel. Does not close or flush
   * either channel.
   *
   * @param from the readable channel to read from
   * @param to the writable channel to write to
   * @return the number of bytes copied
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue
  public static long copy(ReadableByteChannel from, WritableByteChannel to) throws IOException {
    checkNotNull(from);
    checkNotNull(to);
    if (from instanceof FileChannel) {
      FileChannel sourceChannel = (FileChannel) from;
      long oldPosition = sourceChannel.position();
      long position = oldPosition;
      long copied;
      do {
        copied = sourceChannel.transferTo(position, ZERO_COPY_CHUNK_SIZE, to);
        position += copied;
        sourceChannel.position(position);
      } while (copied > 0 || position < sourceChannel.size());
      return position - oldPosition;
    }

    ByteBuffer buf = ByteBuffer.wrap(createBuffer());
    long total = 0;
    while (from.read(buf) != -1) {
      buf.flip();
      while (buf.hasRemaining()) {
        total += to.write(buf);
      }
      buf.clear();
    }
    return total;
  }

  
Max array length on JVM. 
/** Max array length on JVM. */
  private static final int MAX_ARRAY_LEN = Integer.MAX_VALUE - 8;

  
Large enough to never need to expand, given the geometric progression of buffer sizes. 
/** Large enough to never need to expand, given the geometric progression of buffer sizes. */
  private static final int TO_BYTE_ARRAY_DEQUE_SIZE = 20;

  
Returns a byte array containing the bytes from the buffers already in bufs (which have a total combined length of totalLen bytes) followed by all bytes remaining in the given input stream. 
/**
   * Returns a byte array containing the bytes from the buffers already in {@code bufs} (which have
   * a total combined length of {@code totalLen} bytes) followed by all bytes remaining in the given
   * input stream.
   */
  private static byte[] toByteArrayInternal(InputStream in, Deque<byte[]> bufs, int totalLen)
      throws IOException {
    // Starting with an 8k buffer, double the size of each sucessive buffer. Buffers are retained
    // in a deque so that there's no copying between buffers while reading and so all of the bytes
    // in each new allocated buffer are available for reading from the stream.
    for (int bufSize = BUFFER_SIZE;
         totalLen < MAX_ARRAY_LEN;
         bufSize = IntMath.saturatedMultiply(bufSize, 2)) {
      byte[] buf = new byte[Math.min(bufSize, MAX_ARRAY_LEN - totalLen)];
      bufs.add(buf);
      int off = 0;
      while (off < buf.length) {
        // always OK to fill buf; its size plus the rest of bufs is never more than MAX_ARRAY_LEN
        int r = in.read(buf, off, buf.length - off);
        if (r == -1) {
          return combineBuffers(bufs, totalLen);
        }
        off += r;
        totalLen += r;
      }
    }

    // read MAX_ARRAY_LEN bytes without seeing end of stream
    if (in.read() == -1) {
      // oh, there's the end of the stream
      return combineBuffers(bufs, MAX_ARRAY_LEN);
    } else {
      throw new OutOfMemoryError("input is too large to fit in a byte array");
    }
  }

  private static byte[] combineBuffers(Deque<byte[]> bufs, int totalLen) {
    byte[] result = new byte[totalLen];
    int remaining = totalLen;
    while (remaining > 0) {
      byte[] buf = bufs.removeFirst();
      int bytesToCopy = Math.min(remaining, buf.length);
      int resultOffset = totalLen - remaining;
      System.arraycopy(buf, 0, result, resultOffset, bytesToCopy);
      remaining -= bytesToCopy;
    }
    return result;
  }

  
Reads all bytes from an input stream into a byte array. Does not close the stream.

Params:
  • in – the input stream to read from
Throws:
Returns:a byte array containing all the bytes from the stream
/**
   * Reads all bytes from an input stream into a byte array. Does not close the stream.
   *
   * @param in the input stream to read from
   * @return a byte array containing all the bytes from the stream
   * @throws IOException if an I/O error occurs
   */
  public static byte[] toByteArray(InputStream in) throws IOException {
    checkNotNull(in);
    return toByteArrayInternal(in, new ArrayDeque<byte[]>(TO_BYTE_ARRAY_DEQUE_SIZE), 0);
  }

  
Reads all bytes from an input stream into a byte array. The given expected size is used to
create an initial byte array, but if the actual number of bytes read from the stream differs,
the correct result will be returned anyway.

/**
   * Reads all bytes from an input stream into a byte array. The given expected size is used to
   * create an initial byte array, but if the actual number of bytes read from the stream differs,
   * the correct result will be returned anyway.
   */
  static byte[] toByteArray(InputStream in, long expectedSize) throws IOException {
    checkArgument(expectedSize >= 0, "expectedSize (%s) must be non-negative", expectedSize);
    if (expectedSize > MAX_ARRAY_LEN) {
      throw new OutOfMemoryError(expectedSize + " bytes is too large to fit in a byte array");
    }

    byte[] bytes = new byte[(int) expectedSize];
    int remaining = (int) expectedSize;

    while (remaining > 0) {
      int off = (int) expectedSize - remaining;
      int read = in.read(bytes, off, remaining);
      if (read == -1) {
        // end of stream before reading expectedSize bytes
        // just return the bytes read so far
        return Arrays.copyOf(bytes, off);
      }
      remaining -= read;
    }

    // bytes is now full
    int b = in.read();
    if (b == -1) {
      return bytes;
    }

    // the stream was longer, so read the rest normally
    Deque<byte[]> bufs = new ArrayDeque<byte[]>(TO_BYTE_ARRAY_DEQUE_SIZE + 2);
    bufs.add(bytes);
    bufs.add(new byte[] { (byte) b });
    return toByteArrayInternal(in, bufs, bytes.length + 1);
  }

  
Reads and discards data from the given InputStream until the end of the stream is reached. Returns the total number of bytes read. Does not close the stream. 
Since:20.0
/**
   * Reads and discards data from the given {@code InputStream} until the end of the stream is
   * reached. Returns the total number of bytes read. Does not close the stream.
   *
   * @since 20.0
   */
  @CanIgnoreReturnValue
  public static long exhaust(InputStream in) throws IOException {
    long total = 0;
    long read;
    byte[] buf = createBuffer();
    while ((read = in.read(buf)) != -1) {
      total += read;
    }
    return total;
  }

  
Returns a new ByteArrayDataInput instance to read from the bytes array from the beginning. 
/**
   * Returns a new {@link ByteArrayDataInput} instance to read from the {@code bytes} array from the
   * beginning.
   */
  public static ByteArrayDataInput newDataInput(byte[] bytes) {
    return newDataInput(new ByteArrayInputStream(bytes));
  }

  
Returns a new ByteArrayDataInput instance to read from the bytes array, starting at the given position. 
Throws:
/**
   * Returns a new {@link ByteArrayDataInput} instance to read from the {@code bytes} array,
   * starting at the given position.
   *
   * @throws IndexOutOfBoundsException if {@code start} is negative or greater than the length of
   *     the array
   */
  public static ByteArrayDataInput newDataInput(byte[] bytes, int start) {
    checkPositionIndex(start, bytes.length);
    return newDataInput(new ByteArrayInputStream(bytes, start, bytes.length - start));
  }

  
Returns a new ByteArrayDataInput instance to read from the given 
ByteArrayInputStream. The given input stream is not reset before being read from by the returned ByteArrayDataInput. 
Since:17.0
/**
   * Returns a new {@link ByteArrayDataInput} instance to read from the given {@code
   * ByteArrayInputStream}. The given input stream is not reset before being read from by the
   * returned {@code ByteArrayDataInput}.
   *
   * @since 17.0
   */
  public static ByteArrayDataInput newDataInput(ByteArrayInputStream byteArrayInputStream) {
    return new ByteArrayDataInputStream(checkNotNull(byteArrayInputStream));
  }

  private static class ByteArrayDataInputStream implements ByteArrayDataInput {
    final DataInput input;

    ByteArrayDataInputStream(ByteArrayInputStream byteArrayInputStream) {
      this.input = new DataInputStream(byteArrayInputStream);
    }

    @Override
    public void readFully(byte b[]) {
      try {
        input.readFully(b);
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public void readFully(byte b[], int off, int len) {
      try {
        input.readFully(b, off, len);
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public int skipBytes(int n) {
      try {
        return input.skipBytes(n);
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public boolean readBoolean() {
      try {
        return input.readBoolean();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public byte readByte() {
      try {
        return input.readByte();
      } catch (EOFException e) {
        throw new IllegalStateException(e);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public int readUnsignedByte() {
      try {
        return input.readUnsignedByte();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public short readShort() {
      try {
        return input.readShort();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public int readUnsignedShort() {
      try {
        return input.readUnsignedShort();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public char readChar() {
      try {
        return input.readChar();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public int readInt() {
      try {
        return input.readInt();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public long readLong() {
      try {
        return input.readLong();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public float readFloat() {
      try {
        return input.readFloat();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public double readDouble() {
      try {
        return input.readDouble();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public String readLine() {
      try {
        return input.readLine();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }

    @Override
    public String readUTF() {
      try {
        return input.readUTF();
      } catch (IOException e) {
        throw new IllegalStateException(e);
      }
    }
  }

  
Returns a new ByteArrayDataOutput instance with a default size. 
/** Returns a new {@link ByteArrayDataOutput} instance with a default size. */
  public static ByteArrayDataOutput newDataOutput() {
    return newDataOutput(new ByteArrayOutputStream());
  }

  
Returns a new ByteArrayDataOutput instance sized to hold size bytes before resizing. 
Throws:
/**
   * Returns a new {@link ByteArrayDataOutput} instance sized to hold {@code size} bytes before
   * resizing.
   *
   * @throws IllegalArgumentException if {@code size} is negative
   */
  public static ByteArrayDataOutput newDataOutput(int size) {
    // When called at high frequency, boxing size generates too much garbage,
    // so avoid doing that if we can.
    if (size < 0) {
      throw new IllegalArgumentException(String.format("Invalid size: %s", size));
    }
    return newDataOutput(new ByteArrayOutputStream(size));
  }

  
Returns a new ByteArrayDataOutput instance which writes to the given 
ByteArrayOutputStream. The given output stream is not reset before being written to by the returned ByteArrayDataOutput and new data will be appended to any existing content. 
Note that if the given output stream was not empty or is modified after the 
ByteArrayDataOutput is created, the contract for ByteArrayDataOutput.toByteArray will not be honored (the bytes returned in the byte array may not be exactly what was written via calls to ByteArrayDataOutput). 
Since:17.0
/**
   * Returns a new {@link ByteArrayDataOutput} instance which writes to the given {@code
   * ByteArrayOutputStream}. The given output stream is not reset before being written to by the
   * returned {@code ByteArrayDataOutput} and new data will be appended to any existing content.
   *
   * <p>Note that if the given output stream was not empty or is modified after the {@code
   * ByteArrayDataOutput} is created, the contract for {@link ByteArrayDataOutput#toByteArray} will
   * not be honored (the bytes returned in the byte array may not be exactly what was written via
   * calls to {@code ByteArrayDataOutput}).
   *
   * @since 17.0
   */
  public static ByteArrayDataOutput newDataOutput(ByteArrayOutputStream byteArrayOutputSteam) {
    return new ByteArrayDataOutputStream(checkNotNull(byteArrayOutputSteam));
  }

  @SuppressWarnings("deprecation") // for writeBytes
  private static class ByteArrayDataOutputStream implements ByteArrayDataOutput {

    final DataOutput output;
    final ByteArrayOutputStream byteArrayOutputSteam;

    ByteArrayDataOutputStream(ByteArrayOutputStream byteArrayOutputSteam) {
      this.byteArrayOutputSteam = byteArrayOutputSteam;
      output = new DataOutputStream(byteArrayOutputSteam);
    }

    @Override
    public void write(int b) {
      try {
        output.write(b);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void write(byte[] b) {
      try {
        output.write(b);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void write(byte[] b, int off, int len) {
      try {
        output.write(b, off, len);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeBoolean(boolean v) {
      try {
        output.writeBoolean(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeByte(int v) {
      try {
        output.writeByte(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeBytes(String s) {
      try {
        output.writeBytes(s);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeChar(int v) {
      try {
        output.writeChar(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeChars(String s) {
      try {
        output.writeChars(s);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeDouble(double v) {
      try {
        output.writeDouble(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeFloat(float v) {
      try {
        output.writeFloat(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeInt(int v) {
      try {
        output.writeInt(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeLong(long v) {
      try {
        output.writeLong(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeShort(int v) {
      try {
        output.writeShort(v);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public void writeUTF(String s) {
      try {
        output.writeUTF(s);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
    }

    @Override
    public byte[] toByteArray() {
      return byteArrayOutputSteam.toByteArray();
    }
  }

  private static final OutputStream NULL_OUTPUT_STREAM =
      new OutputStream() {
        
Discards the specified byte. 
/** Discards the specified byte. */
        @Override
        public void write(int b) {}

        
Discards the specified byte array. 
/** Discards the specified byte array. */
        @Override
        public void write(byte[] b) {
          checkNotNull(b);
        }

        
Discards the specified byte array. 
/** Discards the specified byte array. */
        @Override
        public void write(byte[] b, int off, int len) {
          checkNotNull(b);
        }

        @Override
        public String toString() {
          return "ByteStreams.nullOutputStream()";
        }
      };

  
Returns an OutputStream that simply discards written bytes. 
Since:14.0 (since 1.0 as com.google.common.io.NullOutputStream)
/**
   * Returns an {@link OutputStream} that simply discards written bytes.
   *
   * @since 14.0 (since 1.0 as com.google.common.io.NullOutputStream)
   */
  public static OutputStream nullOutputStream() {
    return NULL_OUTPUT_STREAM;
  }

  
Wraps a InputStream, limiting the number of bytes which can be read. 
Params:
  • in – the input stream to be wrapped
  • limit – the maximum number of bytes to be read
Returns:a length-limited InputStream
Since:14.0 (since 1.0 as com.google.common.io.LimitInputStream)
/**
   * Wraps a {@link InputStream}, limiting the number of bytes which can be read.
   *
   * @param in the input stream to be wrapped
   * @param limit the maximum number of bytes to be read
   * @return a length-limited {@link InputStream}
   * @since 14.0 (since 1.0 as com.google.common.io.LimitInputStream)
   */
  public static InputStream limit(InputStream in, long limit) {
    return new LimitedInputStream(in, limit);
  }

  private static final class LimitedInputStream extends FilterInputStream {

    private long left;
    private long mark = -1;

    LimitedInputStream(InputStream in, long limit) {
      super(in);
      checkNotNull(in);
      checkArgument(limit >= 0, "limit must be non-negative");
      left = limit;
    }

    @Override
    public int available() throws IOException {
      return (int) Math.min(in.available(), left);
    }

    // it's okay to mark even if mark isn't supported, as reset won't work
    @Override
    public synchronized void mark(int readLimit) {
      in.mark(readLimit);
      mark = left;
    }

    @Override
    public int read() throws IOException {
      if (left == 0) {
        return -1;
      }

      int result = in.read();
      if (result != -1) {
        --left;
      }
      return result;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
      if (left == 0) {
        return -1;
      }

      len = (int) Math.min(len, left);
      int result = in.read(b, off, len);
      if (result != -1) {
        left -= result;
      }
      return result;
    }

    @Override
    public synchronized void reset() throws IOException {
      if (!in.markSupported()) {
        throw new IOException("Mark not supported");
      }
      if (mark == -1) {
        throw new IOException("Mark not set");
      }

      in.reset();
      left = mark;
    }

    @Override
    public long skip(long n) throws IOException {
      n = Math.min(n, left);
      long skipped = in.skip(n);
      left -= skipped;
      return skipped;
    }
  }

  
Attempts to read enough bytes from the stream to fill the given byte array, with the same behavior as DataInput.readFully(byte[]). Does not close the stream. 
Params:
  • in – the input stream to read from.
  • b – the buffer into which the data is read.
Throws:
  • EOFException – if this stream reaches the end before reading all the bytes.
  • IOException – if an I/O error occurs.
/**
   * Attempts to read enough bytes from the stream to fill the given byte array, with the same
   * behavior as {@link DataInput#readFully(byte[])}. Does not close the stream.
   *
   * @param in the input stream to read from.
   * @param b the buffer into which the data is read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  public static void readFully(InputStream in, byte[] b) throws IOException {
    readFully(in, b, 0, b.length);
  }

  
Attempts to read len bytes from the stream into the given array starting at 
off, with the same behavior as DataInput.readFully(byte[], int, int). Does not close the stream. 
Params:
  • in – the input stream to read from.
  • b – the buffer into which the data is read.
  • off – an int specifying the offset into the data.
  • len – an int specifying the number of bytes to read.
Throws:
  • EOFException – if this stream reaches the end before reading all the bytes.
  • IOException – if an I/O error occurs.
/**
   * Attempts to read {@code len} bytes from the stream into the given array starting at {@code
   * off}, with the same behavior as {@link DataInput#readFully(byte[], int, int)}. Does not close
   * the stream.
   *
   * @param in the input stream to read from.
   * @param b the buffer into which the data is read.
   * @param off an int specifying the offset into the data.
   * @param len an int specifying the number of bytes to read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  public static void readFully(InputStream in, byte[] b, int off, int len) throws IOException {
    int read = read(in, b, off, len);
    if (read != len) {
      throw new EOFException(
          "reached end of stream after reading " + read + " bytes; " + len + " bytes expected");
    }
  }

  
Discards n bytes of data from the input stream. This method will block until the full amount has been skipped. Does not close the stream. 
Params:
  • in – the input stream to read from
  • n – the number of bytes to skip
Throws:
  • EOFException – if this stream reaches the end before skipping all the bytes
  • IOException – if an I/O error occurs, or the stream does not support skipping
/**
   * Discards {@code n} bytes of data from the input stream. This method will block until the full
   * amount has been skipped. Does not close the stream.
   *
   * @param in the input stream to read from
   * @param n the number of bytes to skip
   * @throws EOFException if this stream reaches the end before skipping all the bytes
   * @throws IOException if an I/O error occurs, or the stream does not support skipping
   */
  public static void skipFully(InputStream in, long n) throws IOException {
    long skipped = skipUpTo(in, n);
    if (skipped < n) {
      throw new EOFException(
          "reached end of stream after skipping " + skipped + " bytes; " + n + " bytes expected");
    }
  }

  
Discards up to n bytes of data from the input stream. This method will block until either the full amount has been skipped or until the end of the stream is reached, whichever happens first. Returns the total number of bytes skipped. 
/**
   * Discards up to {@code n} bytes of data from the input stream. This method will block until
   * either the full amount has been skipped or until the end of the stream is reached, whichever
   * happens first. Returns the total number of bytes skipped.
   */
  static long skipUpTo(InputStream in, final long n) throws IOException {
    long totalSkipped = 0;
    byte[] buf = createBuffer();

    while (totalSkipped < n) {
      long remaining = n - totalSkipped;
      long skipped = skipSafely(in, remaining);

      if (skipped == 0) {
        // Do a buffered read since skipSafely could return 0 repeatedly, for example if
        // in.available() always returns 0 (the default).
        int skip = (int) Math.min(remaining, buf.length);
        if ((skipped = in.read(buf, 0, skip)) == -1) {
          // Reached EOF
          break;
        }
      }

      totalSkipped += skipped;
    }

    return totalSkipped;
  }

  
Attempts to skip up to n bytes from the given input stream, but not more than 
in.available() bytes. This prevents FileInputStream from skipping more bytes than actually remain in the file, something that it 
specifies it can do in its Javadoc despite the fact that it is violating the contract of InputStream.skip(). 
/**
   * Attempts to skip up to {@code n} bytes from the given input stream, but not more than {@code
   * in.available()} bytes. This prevents {@code FileInputStream} from skipping more bytes than
   * actually remain in the file, something that it {@linkplain java.io.FileInputStream#skip(long)
   * specifies} it can do in its Javadoc despite the fact that it is violating the contract of
   * {@code InputStream.skip()}.
   */
  private static long skipSafely(InputStream in, long n) throws IOException {
    int available = in.available();
    return available == 0 ? 0 : in.skip(Math.min(available, n));
  }

  
Process the bytes of the given input stream using the given processor.

Params:
  • input – the input stream to process
  • processor – the object to which to pass the bytes of the stream
Throws:
Returns:the result of the byte processor
Since:14.0
/**
   * Process the bytes of the given input stream using the given processor.
   *
   * @param input the input stream to process
   * @param processor the object to which to pass the bytes of the stream
   * @return the result of the byte processor
   * @throws IOException if an I/O error occurs
   * @since 14.0
   */
  @CanIgnoreReturnValue // some processors won't return a useful result
  public static <T> T readBytes(InputStream input, ByteProcessor<T> processor) throws IOException {
    checkNotNull(input);
    checkNotNull(processor);

    byte[] buf = createBuffer();
    int read;
    do {
      read = input.read(buf);
    } while (read != -1 && processor.processBytes(buf, 0, read));
    return processor.getResult();
  }

  
Reads some bytes from an input stream and stores them into the buffer array b. This method blocks until len bytes of input data have been read into the array, or end of file is detected. The number of bytes read is returned, possibly zero. Does not close the stream. 
A caller can detect EOF if the number of bytes read is less than len. All subsequent calls on the same stream will return zero. 
If b is null, a NullPointerException is thrown. If off is negative, or len is negative, or off+len is greater than the length of the array 
b, then an IndexOutOfBoundsException is thrown. If len is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. 
Params:
  • in – the input stream to read from
  • b – the buffer into which the data is read
  • off – an int specifying the offset into the data
  • len – an int specifying the number of bytes to read
Throws:
Returns:the number of bytes read
/**
   * Reads some bytes from an input stream and stores them into the buffer array {@code b}. This
   * method blocks until {@code len} bytes of input data have been read into the array, or end of
   * file is detected. The number of bytes read is returned, possibly zero. Does not close the
   * stream.
   *
   * <p>A caller can detect EOF if the number of bytes read is less than {@code len}. All subsequent
   * calls on the same stream will return zero.
   *
   * <p>If {@code b} is null, a {@code NullPointerException} is thrown. If {@code off} is negative,
   * or {@code len} is negative, or {@code off+len} is greater than the length of the array {@code
   * b}, then an {@code IndexOutOfBoundsException} is thrown. If {@code len} is zero, then no bytes
   * are read. Otherwise, the first byte read is stored into element {@code b[off]}, the next one
   * into {@code b[off+1]}, and so on. The number of bytes read is, at most, equal to {@code len}.
   *
   * @param in the input stream to read from
   * @param b the buffer into which the data is read
   * @param off an int specifying the offset into the data
   * @param len an int specifying the number of bytes to read
   * @return the number of bytes read
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue
  // Sometimes you don't care how many bytes you actually read, I guess.
  // (You know that it's either going to read len bytes or stop at EOF.)
  public static int read(InputStream in, byte[] b, int off, int len) throws IOException {
    checkNotNull(in);
    checkNotNull(b);
    if (len < 0) {
      throw new IndexOutOfBoundsException("len is negative");
    }
    int total = 0;
    while (total < len) {
      int result = in.read(b, off + total, len - total);
      if (result == -1) {
        break;
      }
      total += result;
    }
    return total;
  }
}