Java tutorial
/* * Copyright (C) 2012 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.io.ByteStreams.BUF_SIZE; import static com.google.common.io.ByteStreams.skipUpTo; import com.google.common.annotations.Beta; import com.google.common.base.Ascii; import com.google.common.base.Optional; import com.google.common.collect.ImmutableList; import com.google.common.hash.Funnels; import com.google.common.hash.HashCode; import com.google.common.hash.HashFunction; import com.google.common.hash.Hasher; import java.io.BufferedInputStream; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.io.Reader; import java.nio.charset.Charset; import java.util.Arrays; import java.util.Iterator; /** * A readable source of bytes, such as a file. Unlike an {@link InputStream}, a * {@code ByteSource} is not an open, stateful stream for input that can be read and closed. * Instead, it is an immutable <i>supplier</i> of {@code InputStream} instances. * * <p>{@code ByteSource} provides two kinds of methods: * <ul> * <li><b>Methods that return a stream:</b> These methods should return a <i>new</i>, independent * instance each time they are called. The caller is responsible for ensuring that the returned * stream is closed. * <li><b>Convenience methods:</b> These are implementations of common operations that are * typically implemented by opening a stream using one of the methods in the first category, doing * something and finally closing the stream that was opened. * </ul> * * @since 14.0 * @author Colin Decker */ public abstract class ByteSource { /** * Constructor for use by subclasses. */ protected ByteSource() { } /** * Returns a {@link CharSource} view of this byte source that decodes bytes read from this source * as characters using the given {@link Charset}. */ public CharSource asCharSource(Charset charset) { return new AsCharSource(charset); } /** * Opens a new {@link InputStream} for reading from this source. This method should return a new, * independent stream each time it is called. * * <p>The caller is responsible for ensuring that the returned stream is closed. * * @throws IOException if an I/O error occurs in the process of opening the stream */ public abstract InputStream openStream() throws IOException; /** * Opens a new buffered {@link InputStream} for reading from this source. The returned stream is * not required to be a {@link BufferedInputStream} in order to allow implementations to simply * delegate to {@link #openStream()} when the stream returned by that method does not benefit * from additional buffering (for example, a {@code ByteArrayInputStream}). This method should * return a new, independent stream each time it is called. * * <p>The caller is responsible for ensuring that the returned stream is closed. * * @throws IOException if an I/O error occurs in the process of opening the stream * @since 15.0 (in 14.0 with return type {@link BufferedInputStream}) */ public InputStream openBufferedStream() throws IOException { InputStream in = openStream(); return (in instanceof BufferedInputStream) ? (BufferedInputStream) in : new BufferedInputStream(in); } /** * Returns a view of a slice of this byte source that is at most {@code length} bytes long * starting at the given {@code offset}. If {@code offset} is greater than the size of this * source, the returned source will be empty. If {@code offset + length} is greater than the size * of this source, the returned source will contain the slice starting at {@code offset} and * ending at the end of this source. * * @throws IllegalArgumentException if {@code offset} or {@code length} is negative */ public ByteSource slice(long offset, long length) { return new SlicedByteSource(offset, length); } /** * Returns whether the source has zero bytes. The default implementation returns true if * {@link #sizeIfKnown} returns zero, falling back to opening a stream and checking for * EOF if the size is not known. * * <p>Note that, in cases where {@code sizeIfKnown} returns zero, it is <i>possible</i> that bytes * are actually available for reading. (For example, some special files may return a size of 0 * despite actually having content when read.) This means that a source may return {@code true} * from {@code isEmpty()} despite having readable content. * * @throws IOException if an I/O error occurs * @since 15.0 */ public boolean isEmpty() throws IOException { Optional<Long> sizeIfKnown = sizeIfKnown(); if (sizeIfKnown.isPresent() && sizeIfKnown.get() == 0L) { return true; } Closer closer = Closer.create(); try { InputStream in = closer.register(openStream()); return in.read() == -1; } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Returns the size of this source in bytes, if the size can be easily determined without * actually opening the data stream. * * <p>The default implementation returns {@link Optional#absent}. Some sources, such as a file, * may return a non-absent value. Note that in such cases, it is <i>possible</i> that this method * will return a different number of bytes than would be returned by reading all of the bytes (for * example, some special files may return a size of 0 despite actually having content when read). * * <p>Additionally, for mutable sources such as files, a subsequent read may return a different * number of bytes if the contents are changed. * * @since 19.0 */ @Beta public Optional<Long> sizeIfKnown() { return Optional.absent(); } /** * Returns the size of this source in bytes, even if doing so requires opening and traversing * an entire stream. To avoid a potentially expensive operation, see {@link #sizeIfKnown}. * * <p>The default implementation calls {@link #sizeIfKnown} and returns the value if present. * If absent, it will fall back to a heavyweight operation that will open a stream, read (or * {@link InputStream#skip(long) skip}, if possible) to the end of the stream and return the total * number of bytes that were read. * * <p>Note that for some sources that implement {@link #sizeIfKnown} to provide a more efficient * implementation, it is <i>possible</i> that this method will return a different number of bytes * than would be returned by reading all of the bytes (for example, some special files may return * a size of 0 despite actually having content when read). * * <p>In either case, for mutable sources such as files, a subsequent read may return a different * number of bytes if the contents are changed. * * @throws IOException if an I/O error occurs in the process of reading the size of this source */ public long size() throws IOException { Optional<Long> sizeIfKnown = sizeIfKnown(); if (sizeIfKnown.isPresent()) { return sizeIfKnown.get(); } Closer closer = Closer.create(); try { InputStream in = closer.register(openStream()); return countBySkipping(in); } catch (IOException e) { // skip may not be supported... at any rate, try reading } finally { closer.close(); } closer = Closer.create(); try { InputStream in = closer.register(openStream()); return countByReading(in); } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Counts the bytes in the given input stream using skip if possible. Returns SKIP_FAILED if the * first call to skip threw, in which case skip may just not be supported. */ private long countBySkipping(InputStream in) throws IOException { long count = 0; long skipped; while ((skipped = skipUpTo(in, Integer.MAX_VALUE)) > 0) { count += skipped; } return count; } private long countByReading(InputStream in) throws IOException { long count = 0; long read; while ((read = in.read(ByteStreams.skipBuffer)) != -1) { count += read; } return count; } /** * Copies the contents of this byte source to the given {@code OutputStream}. Does not close * {@code output}. * * @throws IOException if an I/O error occurs in the process of reading from this source or * writing to {@code output} */ public long copyTo(OutputStream output) throws IOException { checkNotNull(output); Closer closer = Closer.create(); try { InputStream in = closer.register(openStream()); return ByteStreams.copy(in, output); } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Copies the contents of this byte source to the given {@code ByteSink}. * * @throws IOException if an I/O error occurs in the process of reading from this source or * writing to {@code sink} */ public long copyTo(ByteSink sink) throws IOException { checkNotNull(sink); Closer closer = Closer.create(); try { InputStream in = closer.register(openStream()); OutputStream out = closer.register(sink.openStream()); return ByteStreams.copy(in, out); } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Reads the full contents of this byte source as a byte array. * * @throws IOException if an I/O error occurs in the process of reading from this source */ public byte[] read() throws IOException { Closer closer = Closer.create(); try { InputStream in = closer.register(openStream()); return ByteStreams.toByteArray(in); } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Reads the contents of this byte source using the given {@code processor} to process bytes as * they are read. Stops when all bytes have been read or the consumer returns {@code false}. * Returns the result produced by the processor. * * @throws IOException if an I/O error occurs in the process of reading from this source or if * {@code processor} throws an {@code IOException} * @since 16.0 */ @Beta public <T> T read(ByteProcessor<T> processor) throws IOException { checkNotNull(processor); Closer closer = Closer.create(); try { InputStream in = closer.register(openStream()); return ByteStreams.readBytes(in, processor); } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Hashes the contents of this byte source using the given hash function. * * @throws IOException if an I/O error occurs in the process of reading from this source */ public HashCode hash(HashFunction hashFunction) throws IOException { Hasher hasher = hashFunction.newHasher(); copyTo(Funnels.asOutputStream(hasher)); return hasher.hash(); } /** * Checks that the contents of this byte source are equal to the contents of the given byte * source. * * @throws IOException if an I/O error occurs in the process of reading from this source or * {@code other} */ public boolean contentEquals(ByteSource other) throws IOException { checkNotNull(other); byte[] buf1 = new byte[BUF_SIZE]; byte[] buf2 = new byte[BUF_SIZE]; Closer closer = Closer.create(); try { InputStream in1 = closer.register(openStream()); InputStream in2 = closer.register(other.openStream()); while (true) { int read1 = ByteStreams.read(in1, buf1, 0, BUF_SIZE); int read2 = ByteStreams.read(in2, buf2, 0, BUF_SIZE); if (read1 != read2 || !Arrays.equals(buf1, buf2)) { return false; } else if (read1 != BUF_SIZE) { return true; } } } catch (Throwable e) { throw closer.rethrow(e); } finally { closer.close(); } } /** * Concatenates multiple {@link ByteSource} instances into a single source. Streams returned from * the source will contain the concatenated data from the streams of the underlying sources. * * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will * close the open underlying stream. * * @param sources the sources to concatenate * @return a {@code ByteSource} containing the concatenated data * @since 15.0 */ public static ByteSource concat(Iterable<? extends ByteSource> sources) { return new ConcatenatedByteSource(sources); } /** * Concatenates multiple {@link ByteSource} instances into a single source. Streams returned from * the source will contain the concatenated data from the streams of the underlying sources. * * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will * close the open underlying stream. * * <p>Note: The input {@code Iterator} will be copied to an {@code ImmutableList} when this * method is called. This will fail if the iterator is infinite and may cause problems if the * iterator eagerly fetches data for each source when iterated (rather than producing sources * that only load data through their streams). Prefer using the {@link #concat(Iterable)} * overload if possible. * * @param sources the sources to concatenate * @return a {@code ByteSource} containing the concatenated data * @throws NullPointerException if any of {@code sources} is {@code null} * @since 15.0 */ public static ByteSource concat(Iterator<? extends ByteSource> sources) { return concat(ImmutableList.copyOf(sources)); } /** * Concatenates multiple {@link ByteSource} instances into a single source. Streams returned from * the source will contain the concatenated data from the streams of the underlying sources. * * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will * close the open underlying stream. * * @param sources the sources to concatenate * @return a {@code ByteSource} containing the concatenated data * @throws NullPointerException if any of {@code sources} is {@code null} * @since 15.0 */ public static ByteSource concat(ByteSource... sources) { return concat(ImmutableList.copyOf(sources)); } /** * Returns a view of the given byte array as a {@link ByteSource}. To view only a specific range * in the array, use {@code ByteSource.wrap(b).slice(offset, length)}. * * @since 15.0 (since 14.0 as {@code ByteStreams.asByteSource(byte[])}). */ public static ByteSource wrap(byte[] b) { return new ByteArrayByteSource(b); } /** * Returns an immutable {@link ByteSource} that contains no bytes. * * @since 15.0 */ public static ByteSource empty() { return EmptyByteSource.INSTANCE; } /** * A char source that reads bytes from this source and decodes them as characters using a * charset. */ private final class AsCharSource extends CharSource { private final Charset charset; private AsCharSource(Charset charset) { this.charset = checkNotNull(charset); } @Override public Reader openStream() throws IOException { return new InputStreamReader(ByteSource.this.openStream(), charset); } @Override public String toString() { return ByteSource.this.toString() + ".asCharSource(" + charset + ")"; } } /** * A view of a subsection of the containing byte source. */ private final class SlicedByteSource extends ByteSource { final long offset; final long length; SlicedByteSource(long offset, long length) { checkArgument(offset >= 0, "offset (%s) may not be negative", offset); checkArgument(length >= 0, "length (%s) may not be negative", length); this.offset = offset; this.length = length; } @Override public InputStream openStream() throws IOException { return sliceStream(ByteSource.this.openStream()); } @Override public InputStream openBufferedStream() throws IOException { return sliceStream(ByteSource.this.openBufferedStream()); } private InputStream sliceStream(InputStream in) throws IOException { if (offset > 0) { long skipped; try { skipped = ByteStreams.skipUpTo(in, offset); } catch (Throwable e) { Closer closer = Closer.create(); closer.register(in); try { throw closer.rethrow(e); } finally { closer.close(); } } if (skipped < offset) { // offset was beyond EOF in.close(); return new ByteArrayInputStream(new byte[0]); } } return ByteStreams.limit(in, length); } @Override public ByteSource slice(long offset, long length) { checkArgument(offset >= 0, "offset (%s) may not be negative", offset); checkArgument(length >= 0, "length (%s) may not be negative", length); long maxLength = this.length - offset; return ByteSource.this.slice(this.offset + offset, Math.min(length, maxLength)); } @Override public boolean isEmpty() throws IOException { return length == 0 || super.isEmpty(); } @Override public Optional<Long> sizeIfKnown() { Optional<Long> optionalUnslicedSize = ByteSource.this.sizeIfKnown(); if (optionalUnslicedSize.isPresent()) { long unslicedSize = optionalUnslicedSize.get(); long off = Math.min(offset, unslicedSize); return Optional.of(Math.min(length, unslicedSize - off)); } return Optional.absent(); } @Override public String toString() { return ByteSource.this.toString() + ".slice(" + offset + ", " + length + ")"; } } private static class ByteArrayByteSource extends ByteSource { final byte[] bytes; final int offset; final int length; ByteArrayByteSource(byte[] bytes) { this(bytes, 0, bytes.length); } // NOTE: Preconditions are enforced by slice, the only non-trivial caller. ByteArrayByteSource(byte[] bytes, int offset, int length) { this.bytes = bytes; this.offset = offset; this.length = length; } @Override public InputStream openStream() { return new ByteArrayInputStream(bytes, offset, length); } @Override public InputStream openBufferedStream() throws IOException { return openStream(); } @Override public boolean isEmpty() { return length == 0; } @Override public long size() { return length; } @Override public Optional<Long> sizeIfKnown() { return Optional.of((long) length); } @Override public byte[] read() { return Arrays.copyOfRange(bytes, offset, offset + length); } @Override public long copyTo(OutputStream output) throws IOException { output.write(bytes, offset, length); return length; } @Override public <T> T read(ByteProcessor<T> processor) throws IOException { processor.processBytes(bytes, offset, length); return processor.getResult(); } @Override public HashCode hash(HashFunction hashFunction) throws IOException { return hashFunction.hashBytes(bytes, offset, length); } @Override public ByteSource slice(long offset, long length) { checkArgument(offset >= 0, "offset (%s) may not be negative", offset); checkArgument(length >= 0, "length (%s) may not be negative", length); offset = Math.min(offset, this.length); length = Math.min(length, this.length - offset); int newOffset = this.offset + (int) offset; return new ByteArrayByteSource(bytes, newOffset, (int) length); } @Override public String toString() { return "ByteSource.wrap(" + Ascii.truncate(BaseEncoding.base16().encode(bytes, offset, length), 30, "...") + ")"; } } private static final class EmptyByteSource extends ByteArrayByteSource { static final EmptyByteSource INSTANCE = new EmptyByteSource(); EmptyByteSource() { super(new byte[0]); } @Override public CharSource asCharSource(Charset charset) { checkNotNull(charset); return CharSource.empty(); } @Override public byte[] read() { return bytes; // length is 0, no need to clone } @Override public String toString() { return "ByteSource.empty()"; } } private static final class ConcatenatedByteSource extends ByteSource { final Iterable<? extends ByteSource> sources; ConcatenatedByteSource(Iterable<? extends ByteSource> sources) { this.sources = checkNotNull(sources); } @Override public InputStream openStream() throws IOException { return new MultiInputStream(sources.iterator()); } @Override public boolean isEmpty() throws IOException { for (ByteSource source : sources) { if (!source.isEmpty()) { return false; } } return true; } @Override public Optional<Long> sizeIfKnown() { long result = 0L; for (ByteSource source : sources) { Optional<Long> sizeIfKnown = source.sizeIfKnown(); if (!sizeIfKnown.isPresent()) { return Optional.absent(); } result += sizeIfKnown.get(); } return Optional.of(result); } @Override public long size() throws IOException { long result = 0L; for (ByteSource source : sources) { result += source.size(); } return result; } @Override public String toString() { return "ByteSource.concat(" + sources + ")"; } } }