| /* |
| * 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.Closeable; |
| import java.io.IOException; |
| |
| /** |
| * Abstract base class for input from a file in a {@link Directory}. A |
| * random-access input stream. Used for all Lucene index input operations. |
| * |
| * <p>{@code IndexInput} may only be used from one thread, because it is not |
| * thread safe (it keeps internal state like file position). To allow |
| * multithreaded use, every {@code IndexInput} instance must be cloned before |
| * it is used in another thread. Subclasses must therefore implement {@link #clone()}, |
| * returning a new {@code IndexInput} which operates on the same underlying |
| * resource, but positioned independently. |
| * |
| * <p><b>Warning:</b> Lucene never closes cloned |
| * {@code IndexInput}s, it will only call {@link #close()} on the original object. |
| * |
| * <p>If you access the cloned IndexInput after closing the original object, |
| * any <code>readXXX</code> methods will throw {@link AlreadyClosedException}. |
| * |
| * @see Directory |
| */ |
| public abstract class IndexInput extends DataInput implements Cloneable,Closeable { |
| |
| private final String resourceDescription; |
| |
| /** resourceDescription should be a non-null, opaque string |
| * describing this resource; it's returned from |
| * {@link #toString}. */ |
| protected IndexInput(String resourceDescription) { |
| if (resourceDescription == null) { |
| throw new IllegalArgumentException("resourceDescription must not be null"); |
| } |
| this.resourceDescription = resourceDescription; |
| } |
| |
| /** Closes the stream to further operations. */ |
| @Override |
| public abstract void close() throws IOException; |
| |
| /** Returns the current position in this file, where the next read will |
| * occur. |
| * @see #seek(long) |
| */ |
| public abstract long getFilePointer(); |
| |
| /** Sets current position in this file, where the next read will occur. If this is |
| * beyond the end of the file then this will throw {@code EOFException} and then the |
| * stream is in an undetermined state. |
| * |
| * @see #getFilePointer() |
| */ |
| public abstract void seek(long pos) throws IOException; |
| |
| /** The number of bytes in the file. */ |
| public abstract long length(); |
| |
| @Override |
| public String toString() { |
| return resourceDescription; |
| } |
| |
| /** {@inheritDoc} |
| * |
| * <p><b>Warning:</b> Lucene never closes cloned |
| * {@code IndexInput}s, it will only call {@link #close()} on the original object. |
| * |
| * <p>If you access the cloned IndexInput after closing the original object, |
| * any <code>readXXX</code> methods will throw {@link AlreadyClosedException}. |
| * |
| * <p>This method is NOT thread safe, so if the current {@code IndexInput} |
| * is being used by one thread while {@code clone} is called by another, |
| * disaster could strike. |
| */ |
| @Override |
| public IndexInput clone() { |
| return (IndexInput) super.clone(); |
| } |
| |
| /** |
| * Creates a slice of this index input, with the given description, offset, and length. |
| * The slice is sought to the beginning. |
| */ |
| public abstract IndexInput slice(String sliceDescription, long offset, long length) throws IOException; |
| |
| /** Subclasses call this to get the String for resourceDescription of a slice of this {@code IndexInput}. */ |
| protected String getFullSliceDescription(String sliceDescription) { |
| if (sliceDescription == null) { |
| // Clones pass null sliceDescription: |
| return toString(); |
| } else { |
| return toString() + " [slice=" + sliceDescription + "]"; |
| } |
| } |
| |
| /** |
| * Creates a random-access slice of this index input, with the given offset and length. |
| * <p> |
| * The default implementation calls {@link #slice}, and it doesn't support random access, |
| * it implements absolute reads as seek+read. |
| */ |
| public RandomAccessInput randomAccessSlice(long offset, long length) throws IOException { |
| final IndexInput slice = slice("randomaccess", offset, length); |
| if (slice instanceof RandomAccessInput) { |
| // slice() already supports random access |
| return (RandomAccessInput) slice; |
| } else { |
| // return default impl |
| return new RandomAccessInput() { |
| @Override |
| public byte readByte(long pos) throws IOException { |
| slice.seek(pos); |
| return slice.readByte(); |
| } |
| |
| @Override |
| public short readShort(long pos) throws IOException { |
| slice.seek(pos); |
| return slice.readShort(); |
| } |
| |
| @Override |
| public int readInt(long pos) throws IOException { |
| slice.seek(pos); |
| return slice.readInt(); |
| } |
| |
| @Override |
| public long readLong(long pos) throws IOException { |
| slice.seek(pos); |
| return slice.readLong(); |
| } |
| |
| @Override |
| public String toString() { |
| return "RandomAccessInput(" + IndexInput.this.toString() + ")"; |
| } |
| }; |
| } |
| } |
| } |