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.lucene.store; import java.io.EOFException; import java.io.IOException; /** Base implementation class for buffered {@link IndexInput}. */ public abstract class BufferedIndexInput extends IndexInput implements RandomAccessInput { /** Default buffer size set to {@value #BUFFER_SIZE}. */ public static final int BUFFER_SIZE = 1024; /** Minimum buffer size allowed */ public static final int MIN_BUFFER_SIZE = 8; // The normal read buffer size defaults to 1024, but // increasing this during merging seems to yield // performance gains. However we don't want to increase // it too much because there are quite a few // BufferedIndexInputs created during merging. See // LUCENE-888 for details. /** * A buffer size for merges set to {@value #MERGE_BUFFER_SIZE}. */ public static final int MERGE_BUFFER_SIZE = 4096; private int bufferSize = BUFFER_SIZE; protected byte[] buffer; private long bufferStart = 0; // position in file of buffer private int bufferLength = 0; // end of valid bytes private int bufferPosition = 0; // next byte to read @Override public final byte readByte() throws IOException { if (bufferPosition >= bufferLength) refill(); return buffer[bufferPosition++]; } public BufferedIndexInput(String resourceDesc) { this(resourceDesc, BUFFER_SIZE); } public BufferedIndexInput(String resourceDesc, IOContext context) { this(resourceDesc, bufferSize(context)); } /** Inits BufferedIndexInput with a specific bufferSize */ public BufferedIndexInput(String resourceDesc, int bufferSize) { super(resourceDesc); checkBufferSize(bufferSize); this.bufferSize = bufferSize; } /** Change the buffer size used by this IndexInput */ public final void setBufferSize(int newSize) { assert buffer == null || bufferSize == buffer.length : "buffer=" + buffer + " bufferSize=" + bufferSize + " buffer.length=" + (buffer != null ? buffer.length : 0); if (newSize != bufferSize) { checkBufferSize(newSize); bufferSize = newSize; if (buffer != null) { // Resize the existing buffer and carefully save as // many bytes as possible starting from the current // bufferPosition byte[] newBuffer = new byte[newSize]; final int leftInBuffer = bufferLength - bufferPosition; final int numToCopy; if (leftInBuffer > newSize) numToCopy = newSize; else numToCopy = leftInBuffer; System.arraycopy(buffer, bufferPosition, newBuffer, 0, numToCopy); bufferStart += bufferPosition; bufferPosition = 0; bufferLength = numToCopy; newBuffer(newBuffer); } } } protected void newBuffer(byte[] newBuffer) { // Subclasses can do something here buffer = newBuffer; } /** Returns buffer size. @see #setBufferSize */ public final int getBufferSize() { return bufferSize; } private void checkBufferSize(int bufferSize) { if (bufferSize < MIN_BUFFER_SIZE) throw new IllegalArgumentException( "bufferSize must be at least MIN_BUFFER_SIZE (got " + bufferSize + ")"); } @Override public final void readBytes(byte[] b, int offset, int len) throws IOException { readBytes(b, offset, len, true); } @Override public final void readBytes(byte[] b, int offset, int len, boolean useBuffer) throws IOException { int available = bufferLength - bufferPosition; if (len <= available) { // the buffer contains enough data to satisfy this request if (len > 0) // to allow b to be null if len is 0... System.arraycopy(buffer, bufferPosition, b, offset, len); bufferPosition += len; } else { // the buffer does not have enough data. First serve all we've got. if (available > 0) { System.arraycopy(buffer, bufferPosition, b, offset, available); offset += available; len -= available; bufferPosition += available; } // and now, read the remaining 'len' bytes: if (useBuffer && len < bufferSize) { // If the amount left to read is small enough, and // we are allowed to use our buffer, do it in the usual // buffered way: fill the buffer and copy from it: refill(); if (bufferLength < len) { // Throw an exception when refill() could not read len bytes: System.arraycopy(buffer, 0, b, offset, bufferLength); throw new EOFException("read past EOF: " + this); } else { System.arraycopy(buffer, 0, b, offset, len); bufferPosition = len; } } else { // The amount left to read is larger than the buffer // or we've been asked to not use our buffer - // there's no performance reason not to read it all // at once. Note that unlike the previous code of // this function, there is no need to do a seek // here, because there's no need to reread what we // had in the buffer. long after = bufferStart + bufferPosition + len; if (after > length()) throw new EOFException("read past EOF: " + this); readInternal(b, offset, len); bufferStart = after; bufferPosition = 0; bufferLength = 0; // trigger refill() on read } } } @Override public final short readShort() throws IOException { if (2 <= (bufferLength - bufferPosition)) { return (short) (((buffer[bufferPosition++] & 0xFF) << 8) | (buffer[bufferPosition++] & 0xFF)); } else { return super.readShort(); } } @Override public final int readInt() throws IOException { if (4 <= (bufferLength - bufferPosition)) { return ((buffer[bufferPosition++] & 0xFF) << 24) | ((buffer[bufferPosition++] & 0xFF) << 16) | ((buffer[bufferPosition++] & 0xFF) << 8) | (buffer[bufferPosition++] & 0xFF); } else { return super.readInt(); } } @Override public final long readLong() throws IOException { if (8 <= (bufferLength - bufferPosition)) { final int i1 = ((buffer[bufferPosition++] & 0xff) << 24) | ((buffer[bufferPosition++] & 0xff) << 16) | ((buffer[bufferPosition++] & 0xff) << 8) | (buffer[bufferPosition++] & 0xff); final int i2 = ((buffer[bufferPosition++] & 0xff) << 24) | ((buffer[bufferPosition++] & 0xff) << 16) | ((buffer[bufferPosition++] & 0xff) << 8) | (buffer[bufferPosition++] & 0xff); return (((long) i1) << 32) | (i2 & 0xFFFFFFFFL); } else { return super.readLong(); } } @Override public final int readVInt() throws IOException { if (5 <= (bufferLength - bufferPosition)) { byte b = buffer[bufferPosition++]; if (b >= 0) return b; int i = b & 0x7F; b = buffer[bufferPosition++]; i |= (b & 0x7F) << 7; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7F) << 14; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7F) << 21; if (b >= 0) return i; b = buffer[bufferPosition++]; // Warning: the next ands use 0x0F / 0xF0 - beware copy/paste errors: i |= (b & 0x0F) << 28; if ((b & 0xF0) == 0) return i; throw new IOException("Invalid vInt detected (too many bits)"); } else { return super.readVInt(); } } @Override public final long readVLong() throws IOException { if (9 <= bufferLength - bufferPosition) { byte b = buffer[bufferPosition++]; if (b >= 0) return b; long i = b & 0x7FL; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 7; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 14; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 21; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 28; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 35; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 42; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 49; if (b >= 0) return i; b = buffer[bufferPosition++]; i |= (b & 0x7FL) << 56; if (b >= 0) return i; throw new IOException("Invalid vLong detected (negative values disallowed)"); } else { return super.readVLong(); } } @Override public final byte readByte(long pos) throws IOException { long index = pos - bufferStart; if (index < 0 || index >= bufferLength) { bufferStart = pos; bufferPosition = 0; bufferLength = 0; // trigger refill() on read() seekInternal(pos); refill(); index = 0; } return buffer[(int) index]; } @Override public final short readShort(long pos) throws IOException { long index = pos - bufferStart; if (index < 0 || index >= bufferLength - 1) { bufferStart = pos; bufferPosition = 0; bufferLength = 0; // trigger refill() on read() seekInternal(pos); refill(); index = 0; } return (short) (((buffer[(int) index] & 0xFF) << 8) | (buffer[(int) index + 1] & 0xFF)); } @Override public final int readInt(long pos) throws IOException { long index = pos - bufferStart; if (index < 0 || index >= bufferLength - 3) { bufferStart = pos; bufferPosition = 0; bufferLength = 0; // trigger refill() on read() seekInternal(pos); refill(); index = 0; } return ((buffer[(int) index] & 0xFF) << 24) | ((buffer[(int) index + 1] & 0xFF) << 16) | ((buffer[(int) index + 2] & 0xFF) << 8) | (buffer[(int) index + 3] & 0xFF); } @Override public final long readLong(long pos) throws IOException { long index = pos - bufferStart; if (index < 0 || index >= bufferLength - 7) { bufferStart = pos; bufferPosition = 0; bufferLength = 0; // trigger refill() on read() seekInternal(pos); refill(); index = 0; } final int i1 = ((buffer[(int) index] & 0xFF) << 24) | ((buffer[(int) index + 1] & 0xFF) << 16) | ((buffer[(int) index + 2] & 0xFF) << 8) | (buffer[(int) index + 3] & 0xFF); final int i2 = ((buffer[(int) index + 4] & 0xFF) << 24) | ((buffer[(int) index + 5] & 0xFF) << 16) | ((buffer[(int) index + 6] & 0xFF) << 8) | (buffer[(int) index + 7] & 0xFF); return (((long) i1) << 32) | (i2 & 0xFFFFFFFFL); } private void refill() throws IOException { long start = bufferStart + bufferPosition; long end = start + bufferSize; if (end > length()) // don't read past EOF end = length(); int newLength = (int) (end - start); if (newLength <= 0) throw new EOFException("read past EOF: " + this); if (buffer == null) { newBuffer(new byte[bufferSize]); // allocate buffer lazily seekInternal(bufferStart); } readInternal(buffer, 0, newLength); bufferLength = newLength; bufferStart = start; bufferPosition = 0; } /** Expert: implements buffer refill. Reads bytes from the current position * in the input. * @param b the array to read bytes into * @param offset the offset in the array to start storing bytes * @param length the number of bytes to read */ protected abstract void readInternal(byte[] b, int offset, int length) throws IOException; @Override public final long getFilePointer() { return bufferStart + bufferPosition; } @Override public final void seek(long pos) throws IOException { if (pos >= bufferStart && pos < (bufferStart + bufferLength)) bufferPosition = (int) (pos - bufferStart); // seek within buffer else { bufferStart = pos; bufferPosition = 0; bufferLength = 0; // trigger refill() on read() seekInternal(pos); } } /** Expert: implements seek. Sets current position in this file, where the * next {@link #readInternal(byte[],int,int)} will occur. * @see #readInternal(byte[],int,int) */ protected abstract void seekInternal(long pos) throws IOException; @Override public BufferedIndexInput clone() { BufferedIndexInput clone = (BufferedIndexInput) super.clone(); clone.buffer = null; clone.bufferLength = 0; clone.bufferPosition = 0; clone.bufferStart = getFilePointer(); return clone; } @Override public IndexInput slice(String sliceDescription, long offset, long length) throws IOException { return wrap(sliceDescription, this, offset, length); } /** * Flushes the in-memory buffer to the given output, copying at most * <code>numBytes</code>. * <p> * <b>NOTE:</b> this method does not refill the buffer, however it does * advance the buffer position. * * @return the number of bytes actually flushed from the in-memory buffer. */ protected final int flushBuffer(IndexOutput out, long numBytes) throws IOException { int toCopy = bufferLength - bufferPosition; if (toCopy > numBytes) { toCopy = (int) numBytes; } if (toCopy > 0) { out.writeBytes(buffer, bufferPosition, toCopy); bufferPosition += toCopy; } return toCopy; } /** * Returns default buffer sizes for the given {@link IOContext} */ public static int bufferSize(IOContext context) { switch (context.context) { case MERGE: return MERGE_BUFFER_SIZE; default: return BUFFER_SIZE; } } /** * Wraps a portion of another IndexInput with buffering. * <p><b>Please note:</b> This is in most cases ineffective, because it may double buffer! */ public static BufferedIndexInput wrap(String sliceDescription, IndexInput other, long offset, long length) { return new SlicedIndexInput(sliceDescription, other, offset, length); } /** * Implementation of an IndexInput that reads from a portion of a file. */ private static final class SlicedIndexInput extends BufferedIndexInput { IndexInput base; long fileOffset; long length; SlicedIndexInput(String sliceDescription, IndexInput base, long offset, long length) { super((sliceDescription == null) ? base.toString() : (base.toString() + " [slice=" + sliceDescription + "]"), BufferedIndexInput.BUFFER_SIZE); if (offset < 0 || length < 0 || offset + length > base.length()) { throw new IllegalArgumentException("slice() " + sliceDescription + " out of bounds: " + base); } this.base = base.clone(); this.fileOffset = offset; this.length = length; } @Override public SlicedIndexInput clone() { SlicedIndexInput clone = (SlicedIndexInput) super.clone(); clone.base = base.clone(); clone.fileOffset = fileOffset; clone.length = length; return clone; } @Override protected void readInternal(byte[] b, int offset, int len) throws IOException { long start = getFilePointer(); if (start + len > length) { throw new EOFException("read past EOF: " + this); } base.seek(fileOffset + start); base.readBytes(b, offset, len, false); } @Override protected void seekInternal(long pos) { } @Override public void close() throws IOException { base.close(); } @Override public long length() { return length; } } }