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.FileNotFoundException; import java.io.IOException; import java.nio.file.FileAlreadyExistsException; import java.nio.file.Files; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.List; import java.util.Map; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.atomic.AtomicLong; import org.apache.lucene.index.IndexFileNames; import org.apache.lucene.util.Accountable; import org.apache.lucene.util.Accountables; /** * A memory-resident {@link Directory} implementation. Locking * implementation is by default the {@link SingleInstanceLockFactory}. * * <p><b>Warning:</b> This class is not intended to work with huge * indexes. Everything beyond several hundred megabytes will waste * resources (GC cycles), because it uses an internal buffer size * of 1024 bytes, producing millions of {@code byte[1024]} arrays. * This class is optimized for small memory-resident indexes. * It also has bad concurrency on multithreaded environments. * * <p>It is recommended to materialize large indexes on disk and use * {@link MMapDirectory}, which is a high-performance directory * implementation working directly on the file system cache of the * operating system, so copying data to Java heap space is not useful. * * @deprecated This class uses inefficient synchronization and is discouraged * in favor of {@link MMapDirectory}. It will be removed in future versions * of Lucene. */ @Deprecated public class RAMDirectory extends BaseDirectory implements Accountable { protected final Map<String, RAMFile> fileMap = new ConcurrentHashMap<>(); protected final AtomicLong sizeInBytes = new AtomicLong(); /** Used to generate temp file names in {@link #createTempOutput}. */ private final AtomicLong nextTempFileCounter = new AtomicLong(); /** Constructs an empty {@link Directory}. */ public RAMDirectory() { this(new SingleInstanceLockFactory()); } /** Constructs an empty {@link Directory} with the given {@link LockFactory}. */ public RAMDirectory(LockFactory lockFactory) { super(lockFactory); } /** * Creates a new <code>RAMDirectory</code> instance from a different * <code>Directory</code> implementation. This can be used to load * a disk-based index into memory. * * <p><b>Warning:</b> This class is not intended to work with huge * indexes. Everything beyond several hundred megabytes will waste * resources (GC cycles), because it uses an internal buffer size * of 1024 bytes, producing millions of {@code byte[1024]} arrays. * This class is optimized for small memory-resident indexes. * It also has bad concurrency on multithreaded environments. * * <p>For disk-based indexes it is recommended to use * {@link MMapDirectory}, which is a high-performance directory * implementation working directly on the file system cache of the * operating system, so copying data to Java heap space is not useful. * * <p>Note that the resulting <code>RAMDirectory</code> instance is fully * independent from the original <code>Directory</code> (it is a * complete copy). Any subsequent changes to the * original <code>Directory</code> will not be visible in the * <code>RAMDirectory</code> instance. * * @param dir a <code>Directory</code> value * @exception IOException if an error occurs */ public RAMDirectory(FSDirectory dir, IOContext context) throws IOException { this(dir, false, context); } private RAMDirectory(FSDirectory dir, boolean closeDir, IOContext context) throws IOException { this(); for (String file : dir.listAll()) { if (!Files.isDirectory(dir.getDirectory().resolve(file))) { copyFrom(dir, file, file, context); } } if (closeDir) { dir.close(); } } @Override public final String[] listAll() { ensureOpen(); // NOTE: this returns a "weakly consistent view". Unless we change Dir API, keep this, // and do not synchronize or anything stronger. it's great for testing! // NOTE: fileMap.keySet().toArray(new String[0]) is broken in non Sun JDKs, // and the code below is resilient to map changes during the array population. // NOTE: don't replace this with return names.toArray(new String[names.size()]); // or some files could be null at the end of the array if files are being deleted // concurrently Set<String> fileNames = fileMap.keySet(); List<String> names = new ArrayList<>(fileNames.size()); for (String name : fileNames) { names.add(name); } String[] namesArray = names.toArray(new String[names.size()]); Arrays.sort(namesArray); return namesArray; } public final boolean fileNameExists(String name) { ensureOpen(); return fileMap.containsKey(name); } /** Returns the length in bytes of a file in the directory. * @throws IOException if the file does not exist */ @Override public final long fileLength(String name) throws IOException { ensureOpen(); RAMFile file = fileMap.get(name); if (file == null) { throw new FileNotFoundException(name); } return file.getLength(); } /** * Return total size in bytes of all files in this directory. This is * currently quantized to RAMOutputStream.BUFFER_SIZE. */ @Override public final long ramBytesUsed() { ensureOpen(); return sizeInBytes.get(); } @Override public Collection<Accountable> getChildResources() { return Accountables.namedAccountables("file", fileMap); } @Override public void deleteFile(String name) throws IOException { ensureOpen(); RAMFile file = fileMap.remove(name); if (file != null) { file.directory = null; sizeInBytes.addAndGet(-file.sizeInBytes); } else { throw new FileNotFoundException(name); } } @Override public IndexOutput createOutput(String name, IOContext context) throws IOException { ensureOpen(); RAMFile file = newRAMFile(); if (fileMap.putIfAbsent(name, file) != null) { throw new FileAlreadyExistsException(name); } return new RAMOutputStream(name, file, true); } @Override public IndexOutput createTempOutput(String prefix, String suffix, IOContext context) throws IOException { ensureOpen(); // Make the file first... RAMFile file = newRAMFile(); // ... then try to find a unique name for it: while (true) { String name = IndexFileNames.segmentFileName(prefix, suffix + "_" + Long.toString(nextTempFileCounter.getAndIncrement(), Character.MAX_RADIX), "tmp"); if (fileMap.putIfAbsent(name, file) == null) { return new RAMOutputStream(name, file, true); } } } /** * Returns a new {@link RAMFile} for storing data. This method can be * overridden to return different {@link RAMFile} impls, that e.g. override * {@link RAMFile#newBuffer(int)}. */ protected RAMFile newRAMFile() { return new RAMFile(this); } @Override public void sync(Collection<String> names) throws IOException { } @Override public void rename(String source, String dest) throws IOException { ensureOpen(); RAMFile file = fileMap.get(source); if (file == null) { throw new FileNotFoundException(source); } if (fileMap.putIfAbsent(dest, file) != null) { throw new FileAlreadyExistsException(dest); } if (!fileMap.remove(source, file)) { throw new IllegalStateException("file was unexpectedly replaced: " + source); } fileMap.remove(source); } @Override public void syncMetaData() throws IOException { // we are by definition not durable! } /** Returns a stream reading an existing file. */ @Override public IndexInput openInput(String name, IOContext context) throws IOException { ensureOpen(); RAMFile file = fileMap.get(name); if (file == null) { throw new FileNotFoundException(name); } return new RAMInputStream(name, file); } /** Closes the store to future operations, releasing associated memory. */ @Override public void close() { isOpen = false; fileMap.clear(); } @Override public Set<String> getPendingDeletions() { return Collections.emptySet(); } }