Java tutorial
/** * * 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.hadoop.fs; import java.io.DataInputStream; import java.io.FileDescriptor; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.nio.ByteBuffer; import java.util.EnumSet; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.io.ByteBufferPool; import org.apache.hadoop.util.IdentityHashStore; /** Utility that wraps a {@link FSInputStream} in a {@link DataInputStream} * and buffers input through a {@link java.io.BufferedInputStream}. */ @InterfaceAudience.Public @InterfaceStability.Stable public class FSDataInputStream extends DataInputStream implements Seekable, PositionedReadable, ByteBufferReadable, HasFileDescriptor, CanSetDropBehind, CanSetReadahead, HasEnhancedByteBufferAccess, CanUnbuffer, StreamCapabilities { /** * Map ByteBuffers that we have handed out to readers to ByteBufferPool * objects */ private final IdentityHashStore<ByteBuffer, ByteBufferPool> extendedReadBuffers = new IdentityHashStore<ByteBuffer, ByteBufferPool>( 0); public FSDataInputStream(InputStream in) { super(in); if (!(in instanceof Seekable) || !(in instanceof PositionedReadable)) { throw new IllegalArgumentException("In is not an instance of Seekable or PositionedReadable"); } } /** * Seek to the given offset. * * @param desired offset to seek to */ @Override public void seek(long desired) throws IOException { ((Seekable) in).seek(desired); } /** * Get the current position in the input stream. * * @return current position in the input stream */ @Override public long getPos() throws IOException { return ((Seekable) in).getPos(); } /** * Read bytes from the given position in the stream to the given buffer. * * @param position position in the input stream to seek * @param buffer buffer into which data is read * @param offset offset into the buffer in which data is written * @param length maximum number of bytes to read * @return total number of bytes read into the buffer, or <code>-1</code> * if there is no more data because the end of the stream has been * reached */ @Override public int read(long position, byte[] buffer, int offset, int length) throws IOException { return ((PositionedReadable) in).read(position, buffer, offset, length); } /** * Read bytes from the given position in the stream to the given buffer. * Continues to read until <code>length</code> bytes have been read. * * @param position position in the input stream to seek * @param buffer buffer into which data is read * @param offset offset into the buffer in which data is written * @param length the number of bytes to read * @throws IOException IO problems * @throws EOFException If the end of stream is reached while reading. * If an exception is thrown an undetermined number * of bytes in the buffer may have been written. */ @Override public void readFully(long position, byte[] buffer, int offset, int length) throws IOException { ((PositionedReadable) in).readFully(position, buffer, offset, length); } /** * See {@link #readFully(long, byte[], int, int)}. */ @Override public void readFully(long position, byte[] buffer) throws IOException { ((PositionedReadable) in).readFully(position, buffer, 0, buffer.length); } /** * Seek to the given position on an alternate copy of the data. * * @param targetPos position to seek to * @return true if a new source is found, false otherwise */ @Override public boolean seekToNewSource(long targetPos) throws IOException { return ((Seekable) in).seekToNewSource(targetPos); } /** * Get a reference to the wrapped input stream. Used by unit tests. * * @return the underlying input stream */ @InterfaceAudience.LimitedPrivate({ "HDFS" }) public InputStream getWrappedStream() { return in; } @Override public int read(ByteBuffer buf) throws IOException { if (in instanceof ByteBufferReadable) { return ((ByteBufferReadable) in).read(buf); } throw new UnsupportedOperationException("Byte-buffer read unsupported by input stream"); } @Override public FileDescriptor getFileDescriptor() throws IOException { if (in instanceof HasFileDescriptor) { return ((HasFileDescriptor) in).getFileDescriptor(); } else if (in instanceof FileInputStream) { return ((FileInputStream) in).getFD(); } else { return null; } } @Override public void setReadahead(Long readahead) throws IOException, UnsupportedOperationException { try { ((CanSetReadahead) in).setReadahead(readahead); } catch (ClassCastException e) { throw new UnsupportedOperationException( "this stream does not support setting the readahead " + "caching strategy."); } } @Override public void setDropBehind(Boolean dropBehind) throws IOException, UnsupportedOperationException { try { ((CanSetDropBehind) in).setDropBehind(dropBehind); } catch (ClassCastException e) { throw new UnsupportedOperationException( "this stream does not " + "support setting the drop-behind caching setting."); } } @Override public ByteBuffer read(ByteBufferPool bufferPool, int maxLength, EnumSet<ReadOption> opts) throws IOException, UnsupportedOperationException { try { return ((HasEnhancedByteBufferAccess) in).read(bufferPool, maxLength, opts); } catch (ClassCastException e) { ByteBuffer buffer = ByteBufferUtil.fallbackRead(this, bufferPool, maxLength); if (buffer != null) { extendedReadBuffers.put(buffer, bufferPool); } return buffer; } } private static final EnumSet<ReadOption> EMPTY_READ_OPTIONS_SET = EnumSet.noneOf(ReadOption.class); final public ByteBuffer read(ByteBufferPool bufferPool, int maxLength) throws IOException, UnsupportedOperationException { return read(bufferPool, maxLength, EMPTY_READ_OPTIONS_SET); } @Override public void releaseBuffer(ByteBuffer buffer) { try { ((HasEnhancedByteBufferAccess) in).releaseBuffer(buffer); } catch (ClassCastException e) { ByteBufferPool bufferPool = extendedReadBuffers.remove(buffer); if (bufferPool == null) { throw new IllegalArgumentException( "tried to release a buffer " + "that was not created by this stream."); } bufferPool.putBuffer(buffer); } } @Override public void unbuffer() { StreamCapabilitiesPolicy.unbuffer(in); } @Override public boolean hasCapability(String capability) { if (in instanceof StreamCapabilities) { return ((StreamCapabilities) in).hasCapability(capability); } return false; } /** * String value. Includes the string value of the inner stream * @return the stream */ @Override public String toString() { return super.toString() + ": " + in; } }