Java tutorial
/** * Copyright 2010-present Facebook. * * 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.facebook.internal; import android.content.Context; import android.util.Log; import com.facebook.LoggingBehavior; import com.facebook.Settings; import org.json.JSONException; import org.json.JSONObject; import org.json.JSONTokener; import java.io.*; import java.security.InvalidParameterException; import java.util.Date; import java.util.PriorityQueue; import java.util.concurrent.atomic.AtomicLong; // This class is intended to be thread-safe. // // There are two classes of files: buffer files and cache files: // - A buffer file is in the process of being written, and there is an open stream on the file. These files are // named as "bufferN" where N is an incrementing integer. On startup, we delete all existing files of this form. // Once the stream is closed, we rename the buffer file to a cache file or attempt to delete if this fails. We // do not otherwise ever attempt to delete these files. // - A cache file is a non-changing file that is named by the md5 hash of the cache key. We monitor the size of // these files in aggregate and remove the oldest one(s) to stay under quota. This process does not block threads // calling into this class, so theoretically we could go arbitrarily over quota but in practice this should not // happen because deleting files should be much cheaper than downloading new file content. // // Since there can only ever be one thread accessing a particular buffer file, we do not synchronize access to these. // We do assume that file rename is atomic when converting a buffer file to a cache file, and that if multiple files // are renamed to a single target that exactly one of them continues to exist. // // Standard POSIX file semantics guarantee being able to continue to use a file handle even after the // corresponding file has been deleted. Given this and that cache files never change other than deleting in trim() // or clear(), we only have to ensure that there is at most one trim() or clear() process deleting files at any // given time. /** * com.facebook.internal is solely for the use of other packages within the Facebook SDK for Android. Use of * any of the classes in this package is unsupported, and they may be modified or removed without warning at * any time. */ public final class FileLruCache { static final String TAG = FileLruCache.class.getSimpleName(); private static final String HEADER_CACHEKEY_KEY = "key"; private static final String HEADER_CACHE_CONTENT_TAG_KEY = "tag"; private static final AtomicLong bufferIndex = new AtomicLong(); private final String tag; private final Limits limits; private final File directory; private boolean isTrimPending; private boolean isTrimInProgress; private final Object lock; private AtomicLong lastClearCacheTime = new AtomicLong(0); // The value of tag should be a final String that works as a directory name. public FileLruCache(Context context, String tag, Limits limits) { this.tag = tag; this.limits = limits; this.directory = new File(context.getCacheDir(), tag); this.lock = new Object(); // Ensure the cache dir exists if (this.directory.mkdirs() || this.directory.isDirectory()) { // Remove any stale partially-written files from a previous run BufferFile.deleteAll(this.directory); } } // This is not robust to files changing dynamically underneath it and should therefore only be used // for test code. If we ever need this for product code we need to think through synchronization. // See the threading notes at the top of this class. // // Also, since trim() runs asynchronously now, this blocks until any pending trim has completed. long sizeInBytesForTest() { synchronized (lock) { while (isTrimPending || isTrimInProgress) { try { lock.wait(); } catch (InterruptedException e) { // intentional no-op } } } File[] files = this.directory.listFiles(); long total = 0; if (files != null) { for (File file : files) { total += file.length(); } } return total; } public InputStream get(String key) throws IOException { return get(key, null); } public InputStream get(String key, String contentTag) throws IOException { File file = new File(this.directory, Utility.md5hash(key)); FileInputStream input = null; try { input = new FileInputStream(file); } catch (IOException e) { return null; } BufferedInputStream buffered = new BufferedInputStream(input, Utility.DEFAULT_STREAM_BUFFER_SIZE); boolean success = false; try { JSONObject header = StreamHeader.readHeader(buffered); if (header == null) { return null; } String foundKey = header.optString(HEADER_CACHEKEY_KEY); if ((foundKey == null) || !foundKey.equals(key)) { return null; } String headerContentTag = header.optString(HEADER_CACHE_CONTENT_TAG_KEY, null); if ((contentTag == null && headerContentTag != null) || (contentTag != null && !contentTag.equals(headerContentTag))) { return null; } long accessTime = new Date().getTime(); Logger.log(LoggingBehavior.CACHE, TAG, "Setting lastModified to " + Long.valueOf(accessTime) + " for " + file.getName()); file.setLastModified(accessTime); success = true; return buffered; } finally { if (!success) { buffered.close(); } } } OutputStream openPutStream(final String key) throws IOException { return openPutStream(key, null); } public OutputStream openPutStream(final String key, String contentTag) throws IOException { final File buffer = BufferFile.newFile(this.directory); buffer.delete(); if (!buffer.createNewFile()) { throw new IOException("Could not create file at " + buffer.getAbsolutePath()); } FileOutputStream file = null; try { file = new FileOutputStream(buffer); } catch (FileNotFoundException e) { Logger.log(LoggingBehavior.CACHE, Log.WARN, TAG, "Error creating buffer output stream: " + e); throw new IOException(e.getMessage()); } final long bufferFileCreateTime = System.currentTimeMillis(); StreamCloseCallback renameToTargetCallback = new StreamCloseCallback() { @Override public void onClose() { // if the buffer file was created before the cache was cleared, then the buffer file // should be deleted rather than renamed and saved. if (bufferFileCreateTime < lastClearCacheTime.get()) { buffer.delete(); } else { renameToTargetAndTrim(key, buffer); } } }; CloseCallbackOutputStream cleanup = new CloseCallbackOutputStream(file, renameToTargetCallback); BufferedOutputStream buffered = new BufferedOutputStream(cleanup, Utility.DEFAULT_STREAM_BUFFER_SIZE); boolean success = false; try { // Prefix the stream with the actual key, since there could be collisions JSONObject header = new JSONObject(); header.put(HEADER_CACHEKEY_KEY, key); if (!Utility.isNullOrEmpty(contentTag)) { header.put(HEADER_CACHE_CONTENT_TAG_KEY, contentTag); } StreamHeader.writeHeader(buffered, header); success = true; return buffered; } catch (JSONException e) { // JSON is an implementation detail of the cache, so don't let JSON exceptions out. Logger.log(LoggingBehavior.CACHE, Log.WARN, TAG, "Error creating JSON header for cache file: " + e); throw new IOException(e.getMessage()); } finally { if (!success) { buffered.close(); } } } public void clearCache() { // get the current directory listing of files to delete final File[] filesToDelete = directory.listFiles(BufferFile.excludeBufferFiles()); lastClearCacheTime.set(System.currentTimeMillis()); if (filesToDelete != null) { Settings.getExecutor().execute(new Runnable() { @Override public void run() { for (File file : filesToDelete) { file.delete(); } } }); } } private void renameToTargetAndTrim(String key, File buffer) { final File target = new File(directory, Utility.md5hash(key)); // This is triggered by close(). By the time close() returns, the file should be cached, so this needs to // happen synchronously on this thread. // // However, it does not need to be synchronized, since in the race we will just start an unnecesary trim // operation. Avoiding the cost of holding the lock across the file operation seems worth this cost. if (!buffer.renameTo(target)) { buffer.delete(); } postTrim(); } // Opens an output stream for the key, and creates an input stream wrapper to copy // the contents of input into the new output stream. The effect is to store a // copy of input, and associate that data with key. public InputStream interceptAndPut(String key, InputStream input) throws IOException { OutputStream output = openPutStream(key); return new CopyingInputStream(input, output); } public String toString() { return "{FileLruCache:" + " tag:" + this.tag + " file:" + this.directory.getName() + "}"; } private void postTrim() { synchronized (lock) { if (!isTrimPending) { isTrimPending = true; Settings.getExecutor().execute(new Runnable() { @Override public void run() { trim(); } }); } } } private void trim() { synchronized (lock) { isTrimPending = false; isTrimInProgress = true; } try { Logger.log(LoggingBehavior.CACHE, TAG, "trim started"); PriorityQueue<ModifiedFile> heap = new PriorityQueue<ModifiedFile>(); long size = 0; long count = 0; File[] filesToTrim = this.directory.listFiles(BufferFile.excludeBufferFiles()); if (filesToTrim != null) { for (File file : filesToTrim) { ModifiedFile modified = new ModifiedFile(file); heap.add(modified); Logger.log(LoggingBehavior.CACHE, TAG, " trim considering time=" + Long.valueOf(modified.getModified()) + " name=" + modified.getFile().getName()); size += file.length(); count++; } } while ((size > limits.getByteCount()) || (count > limits.getFileCount())) { File file = heap.remove().getFile(); Logger.log(LoggingBehavior.CACHE, TAG, " trim removing " + file.getName()); size -= file.length(); count--; file.delete(); } } finally { synchronized (lock) { isTrimInProgress = false; lock.notifyAll(); } } } private static class BufferFile { private static final String FILE_NAME_PREFIX = "buffer"; private static final FilenameFilter filterExcludeBufferFiles = new FilenameFilter() { @Override public boolean accept(File dir, String filename) { return !filename.startsWith(FILE_NAME_PREFIX); } }; private static final FilenameFilter filterExcludeNonBufferFiles = new FilenameFilter() { @Override public boolean accept(File dir, String filename) { return filename.startsWith(FILE_NAME_PREFIX); } }; static void deleteAll(final File root) { File[] filesToDelete = root.listFiles(excludeNonBufferFiles()); if (filesToDelete != null) { for (File file : filesToDelete) { file.delete(); } } } static FilenameFilter excludeBufferFiles() { return filterExcludeBufferFiles; } static FilenameFilter excludeNonBufferFiles() { return filterExcludeNonBufferFiles; } static File newFile(final File root) { String name = FILE_NAME_PREFIX + Long.valueOf(bufferIndex.incrementAndGet()).toString(); return new File(root, name); } } // Treats the first part of a stream as a header, reads/writes it as a JSON blob, and // leaves the stream positioned exactly after the header. // // The format is as follows: // byte: meaning // --------------------------------- // 0: version number // 1-3: big-endian JSON header blob size // 4-size+4: UTF-8 JSON header blob // ...: stream data private static final class StreamHeader { private static final int HEADER_VERSION = 0; static void writeHeader(OutputStream stream, JSONObject header) throws IOException { String headerString = header.toString(); byte[] headerBytes = headerString.getBytes(); // Write version number and big-endian header size stream.write(HEADER_VERSION); stream.write((headerBytes.length >> 16) & 0xff); stream.write((headerBytes.length >> 8) & 0xff); stream.write((headerBytes.length >> 0) & 0xff); stream.write(headerBytes); } static JSONObject readHeader(InputStream stream) throws IOException { int version = stream.read(); if (version != HEADER_VERSION) { return null; } int headerSize = 0; for (int i = 0; i < 3; i++) { int b = stream.read(); if (b == -1) { Logger.log(LoggingBehavior.CACHE, TAG, "readHeader: stream.read returned -1 while reading header size"); return null; } headerSize <<= 8; headerSize += b & 0xff; } byte[] headerBytes = new byte[headerSize]; int count = 0; while (count < headerBytes.length) { int readCount = stream.read(headerBytes, count, headerBytes.length - count); if (readCount < 1) { Logger.log(LoggingBehavior.CACHE, TAG, "readHeader: stream.read stopped at " + Integer.valueOf(count) + " when expected " + headerBytes.length); return null; } count += readCount; } String headerString = new String(headerBytes); JSONObject header = null; JSONTokener tokener = new JSONTokener(headerString); try { Object parsed = tokener.nextValue(); if (!(parsed instanceof JSONObject)) { Logger.log(LoggingBehavior.CACHE, TAG, "readHeader: expected JSONObject, got " + parsed.getClass().getCanonicalName()); return null; } header = (JSONObject) parsed; } catch (JSONException e) { throw new IOException(e.getMessage()); } return header; } } private static class CloseCallbackOutputStream extends OutputStream { final OutputStream innerStream; final StreamCloseCallback callback; CloseCallbackOutputStream(OutputStream innerStream, StreamCloseCallback callback) { this.innerStream = innerStream; this.callback = callback; } @Override public void close() throws IOException { try { this.innerStream.close(); } finally { this.callback.onClose(); } } @Override public void flush() throws IOException { this.innerStream.flush(); } @Override public void write(byte[] buffer, int offset, int count) throws IOException { this.innerStream.write(buffer, offset, count); } @Override public void write(byte[] buffer) throws IOException { this.innerStream.write(buffer); } @Override public void write(int oneByte) throws IOException { this.innerStream.write(oneByte); } } private static final class CopyingInputStream extends InputStream { final InputStream input; final OutputStream output; CopyingInputStream(final InputStream input, final OutputStream output) { this.input = input; this.output = output; } @Override public int available() throws IOException { return input.available(); } @Override public void close() throws IOException { // According to http://www.cs.cornell.edu/andru/javaspec/11.doc.html: // "If a finally clause is executed because of abrupt completion of a try block and the finally clause // itself completes abruptly, then the reason for the abrupt completion of the try block is discarded // and the new reason for abrupt completion is propagated from there." // // Android does appear to behave like this. try { this.input.close(); } finally { this.output.close(); } } @Override public void mark(int readlimit) { throw new UnsupportedOperationException(); } @Override public boolean markSupported() { return false; } @Override public int read(byte[] buffer) throws IOException { int count = input.read(buffer); if (count > 0) { output.write(buffer, 0, count); } return count; } @Override public int read() throws IOException { int b = input.read(); if (b >= 0) { output.write(b); } return b; } @Override public int read(byte[] buffer, int offset, int length) throws IOException { int count = input.read(buffer, offset, length); if (count > 0) { output.write(buffer, offset, count); } return count; } @Override public synchronized void reset() { throw new UnsupportedOperationException(); } @Override public long skip(long byteCount) throws IOException { byte[] buffer = new byte[1024]; long total = 0; while (total < byteCount) { int count = read(buffer, 0, (int) Math.min(byteCount - total, buffer.length)); if (count < 0) { return total; } total += count; } return total; } } public static final class Limits { private int byteCount; private int fileCount; public Limits() { // A Samsung Galaxy Nexus can create 1k files in half a second. By the time // it gets to 5k files it takes 5 seconds. 10k files took 15 seconds. This // continues to slow down as files are added. This assumes all files are in // a single directory. // // Following a git-like strategy where we partition MD5-named files based on // the first 2 characters is slower across the board. this.fileCount = 1024; this.byteCount = 1024 * 1024; } int getByteCount() { return byteCount; } int getFileCount() { return fileCount; } void setByteCount(int n) { if (n < 0) { throw new InvalidParameterException("Cache byte-count limit must be >= 0"); } byteCount = n; } void setFileCount(int n) { if (n < 0) { throw new InvalidParameterException("Cache file count limit must be >= 0"); } fileCount = n; } } // Caches the result of lastModified during sort/heap operations private final static class ModifiedFile implements Comparable<ModifiedFile> { private static final int HASH_SEED = 29; // Some random prime number private static final int HASH_MULTIPLIER = 37; // Some random prime number private final File file; private final long modified; ModifiedFile(File file) { this.file = file; this.modified = file.lastModified(); } File getFile() { return file; } long getModified() { return modified; } @Override public int compareTo(ModifiedFile another) { if (getModified() < another.getModified()) { return -1; } else if (getModified() > another.getModified()) { return 1; } else { return getFile().compareTo(another.getFile()); } } @Override public boolean equals(Object another) { return (another instanceof ModifiedFile) && (compareTo((ModifiedFile) another) == 0); } @Override public int hashCode() { int result = HASH_SEED; result = (result * HASH_MULTIPLIER) + file.hashCode(); result = (result * HASH_MULTIPLIER) + (int) (modified % Integer.MAX_VALUE); return result; } } private interface StreamCloseCallback { void onClose(); } }