Java tutorial
/* * 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 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.Arrays; /** * Provides utility methods for working with byte arrays and I/O streams. * * @author Chris Nokleberg * @author Colin Decker * @since 1.0 */ @Beta public final class ByteStreams { /** * Default size of buffers allocated for copies. */ static final int BUF_SIZE = 8192; /** * A buffer for skipping bytes in an input stream. Only written to and never read, so actual * contents don't matter. */ static final byte[] skipBuffer = new byte[BUF_SIZE]; /** * 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> * <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> * <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.</li> * </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. * * @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 */ public static long copy(InputStream from, OutputStream to) throws IOException { checkNotNull(from); checkNotNull(to); byte[] buf = new byte[BUF_SIZE]; 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. * * @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 */ 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.allocate(BUF_SIZE); long total = 0; while (from.read(buf) != -1) { buf.flip(); while (buf.hasRemaining()) { total += to.write(buf); } buf.clear(); } return total; } /** * 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 { ByteArrayOutputStream out = new ByteArrayOutputStream(); copy(in, out); return out.toByteArray(); } /** * 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, int expectedSize) throws IOException { byte[] bytes = new byte[expectedSize]; int remaining = expectedSize; while (remaining > 0) { int off = 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 FastByteArrayOutputStream out = new FastByteArrayOutputStream(); out.write(b); // write the byte we read when testing for end of stream copy(in, out); byte[] result = new byte[bytes.length + out.size()]; System.arraycopy(bytes, 0, result, 0, bytes.length); out.writeTo(result, bytes.length); return result; } /** * BAOS that provides limited access to its internal byte array. */ private static final class FastByteArrayOutputStream extends ByteArrayOutputStream { /** * Writes the contents of the internal buffer to the given array starting * at the given offset. Assumes the array has space to hold count bytes. */ void writeTo(byte[] b, int off) { System.arraycopy(buf, 0, b, off, count); } } /** * 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 {@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 {@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 {@link ByteArrayDataOutput} instance with a default size. */ public static ByteArrayDataOutput newDataOutput() { return newDataOutput(new ByteArrayOutputStream()); } /** * 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 {@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. */ @Override public void write(int b) { } /** Discards the specified byte array. */ @Override public void write(byte[] b) { checkNotNull(b); } /** 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 {@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 {@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 {@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 {@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 {@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 {@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; 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, skipBuffer.length); if ((skipped = in.read(skipBuffer, 0, skip)) == -1) { // Reached EOF break; } } totalSkipped += skipped; } return totalSkipped; } /** * 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 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. * * @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 */ public static <T> T readBytes(InputStream input, ByteProcessor<T> processor) throws IOException { checkNotNull(input); checkNotNull(processor); byte[] buf = new byte[BUF_SIZE]; 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 * {@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 */ 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; } }