Java tutorial
/** * Copyright 2010 Facebook, Inc. * * 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; import android.content.Context; import android.util.Log; 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; 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; // The value of tag should be a final String that works as a directory name. FileLruCache(Context context, String tag, Limits limits) { this.tag = tag; this.limits = limits; this.directory = new File(context.getCacheDir(), tag); // Ensure the cache dir exists this.directory.mkdirs(); // Remove any stale partially-written files from a previous run BufferFile.deleteAll(this.directory); } void clear() throws IOException { for (File file : this.directory.listFiles()) { file.delete(); } } InputStream get(String key) throws IOException { return get(key, null); } 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 (headerContentTag != contentTag) { return null; } long accessTime = new Date().getTime(); Logger.log(LoggingBehaviors.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); } 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(LoggingBehaviors.CACHE, Log.WARN, TAG, "Error creating buffer output stream: " + e); throw new IOException(e.getMessage()); } StreamCloseCallback renameToTargetCallback = new StreamCloseCallback() { @Override public void onClose() { final File target = new File(directory, Utility.md5hash(key)); if (!buffer.renameTo(target)) { buffer.delete(); } trim(); } }; 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(LoggingBehaviors.CACHE, Log.WARN, TAG, "Error creating JSON header for cache file: " + e); throw new IOException(e.getMessage()); } finally { if (!success) { buffered.close(); } } } // 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. InputStream interceptAndPut(String key, InputStream input) throws IOException { OutputStream output = openPutStream(key); return new CopyingInputStream(input, output); } long sizeInBytes() { File[] files = this.directory.listFiles(); long total = 0; for (File file : files) { total += file.length(); } return total; } public synchronized String toString() { return "{FileLruCache:" + " tag:" + this.tag + " file:" + this.directory.getName() + "}"; } private void trim() { Logger.log(LoggingBehaviors.CACHE, TAG, "trim started"); PriorityQueue<ModifiedFile> heap = new PriorityQueue<ModifiedFile>(); long size = 0; long count = 0; for (File file : this.directory.listFiles(BufferFile.excludeBufferFiles())) { ModifiedFile modified = new ModifiedFile(file); heap.add(modified); Logger.log(LoggingBehaviors.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(LoggingBehaviors.CACHE, TAG, " trim removing " + file.getName()); size -= file.length(); count--; file.delete(); } } 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) { for (File file : root.listFiles(excludeNonBufferFiles())) { 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(LoggingBehaviors.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(LoggingBehaviors.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(LoggingBehaviors.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; } } static final class Limits { private int byteCount; private int fileCount; 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 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); } } private interface StreamCloseCallback { void onClose(); } }