安卓开发笔记——关于图片的三级缓存策略(内存LruCache+磁盘DiskLruCache+网络Volley)

9/6/2015来源:Java教程人气:2207

安卓开发笔记——关于图片的三级缓存策略(内存LruCache+磁盘DiskLruCache+网络Volley)

  在开发安卓应用中避免不了要使用到网络图片,获取网络图片很简单,但是需要付出一定的代价——流量。对于少数的图片而言问题不大,但如果手机应用中包含大量的图片,这势必会耗费用户的一定流量,如果我们不加以处理,每次打开应用都去网络获取图片,那么用户可就不乐意了,这里的处理就是指今天要讲的缓存策略(缓存层分为三层:内存层,磁盘层,网络层)。

  关于缓存层的工作,当我们第一次打开应用获取图片时,先到网络去下载图片,然后依次存入内存缓存,磁盘缓存,当我们再一次需要用到刚才下载的这张图片时,就不需要再重复的到网络上去下载,直接可以从内存缓存和磁盘缓存中找,由于内存缓存速度较快,我们优先到内存缓存中寻找该图片,如果找到则运用,如果没有找到(内存缓存大小有限),那么我们再到磁盘缓存中去找。只要我们合理的去协调这三层缓存运用,便可以提升应用性能和用户体验。

1、内存层:(手机内存)

内存缓存相对于磁盘缓存而言,速度要来的快很多,但缺点容量较小且会被系统回收,这里的实现我用到了LruCache。

LruCache这个类是Android3.1版本中提供的,如果你是在更早的Android版本中开发,则需要导入android-support-v4的jar包。

磁盘层:(SD卡)

相比内存缓存而言速度要来得慢很多,但容量很大,这里的实现我用到了DiskLruCache类。

DiskLruCache是非Google官方编写,但获得官方认证的硬盘缓存类,该类没有限定在Android内,所以理论上java应用也可以使用DiskLreCache来缓存。

这是DiskLruCache类的下载地址:http://pan.baidu.com/s/1hq0D53m

网络层:(移动网络,无线网络)

这个就没什么解释的了,就是我们上网用的流量。这里的网络访问实现我用到了开源框架Volley。

开源框架Volley是2013年Google I/O大会发布的,Volley是Android平台上的网络通信库,能使网络通信更快,更简单,更健壮。它的设计目标就是非常适合去进行数据量不大,但通信频繁的网络操作,而对于大数据量的网络操作,比如说下载文件等,Volley的表现就会非常糟糕。

这是Volley的下载地址:http://pan.baidu.com/s/1hq1t2yo

先来看下效果图:

正常网络下:     断开网络,飞行模式下:

      

Log日志打印:

来看下代码实现:

1、由于应用中很多地方需要用到上下文对象,这里我自定义了一个全局的application,用来提供上下文对象

 1 package com.lcw.rabbit.image.utils; 2  3 import android.app.Application; 4 /** 5  * Application类,提供全局上下文对象 6  * @author Rabbit_Lee 7  * 8  */ 9 public class MyApplication extends Application {10 11     public static String TAG;12     public static MyApplication myApplication;13 14     public static MyApplication newInstance() {15         return myApplication;16     }17 18     @Override19     public void onCreate() {20         super.onCreate();21         TAG = this.getClass().getSimpleName();22         myApplication = this;23 24     }25 }

2、Volley请求队列处理类,用来管理Rquest请求对象操作

 1 package com.lcw.rabbit.image; 2  3 import com.android.volley.Request; 4 import com.android.volley.RequestQueue; 5 import com.android.volley.toolbox.Volley; 6 import com.lcw.rabbit.image.utils.MyApplication; 7  8 /** 9  * 请求队列处理类10  * 获取RequestQueue对象11  */12 public class VolleyRequestQueueManager {13     // 获取请求队列类14     public static RequestQueue mRequestQueue = Volley.newRequestQueue(MyApplication.newInstance());15 16     //添加任务进任务队列17     public static void addRequest(Request<?> request, Object tag) {18         if (tag != null) {19             request.setTag(tag);20         }21         mRequestQueue.add(request);22     }23     24     //取消任务25     public static void cancelRequest(Object tag){26         mRequestQueue.cancelAll(tag);27     }28     29     30 31 }

3、这里附上2个工具类(生成md5序列帮助类,DiskLruCache磁盘缓存类)

 1 package com.lcw.rabbit.image.utils; 2  3 import java.math.BigInteger; 4 import java.security.MessageDigest; 5 import java.security.NoSuchAlgorithmException; 6  7 public class MD5Utils { 8     /** 9      * 使用md5的算法进行加密10      */11     public static String md5(String plainText) {12         byte[] secretBytes = null;13         try {14             secretBytes = MessageDigest.getInstance("md5").digest(15                     plainText.getBytes());16         } catch (NoSuchAlgorithmException e) {17             throw new RuntimeException("没有md5这个算法!");18         }19         String md5code = new BigInteger(1, secretBytes).toString(16);// 16进制数字20         // 如果生成数字未满32位,需要前面补021         for (int i = 0; i < 32 - md5code.length(); i++) {22             md5code = "0" + md5code;23         }24         return md5code;25     }26 27 }
MD5转换类

  1 /*  2  * Copyright (C) 2011 The Android Open Source PRoject  3  *  4  * Licensed under the Apache License, Version 2.0 (the "License");  5  * you may not use this file except in compliance with the License.  6  * You may obtain a copy of the License at  7  *  8  *      http://www.apache.org/licenses/LICENSE-2.0  9  * 10  * Unless required by applicable law or agreed to in writing, software 11  * distributed under the License is distributed on an "AS IS" BASIS, 12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13  * See the License for the specific language governing permissions and 14  * limitations under the License. 15  */ 16  17 package com.lcw.rabbit.image.utils; 18  19 import java.io.BufferedInputStream; 20 import java.io.BufferedWriter; 21 import java.io.Closeable; 22 import java.io.EOFException; 23 import java.io.File; 24 import java.io.FileInputStream; 25 import java.io.FileNotFoundException; 26 import java.io.FileOutputStream; 27 import java.io.FileWriter; 28 import java.io.FilterOutputStream; 29 import java.io.IOException; 30 import java.io.InputStream; 31 import java.io.InputStreamReader; 32 import java.io.OutputStream; 33 import java.io.OutputStreamWriter; 34 import java.io.Reader; 35 import java.io.StringWriter; 36 import java.io.Writer; 37 import java.lang.reflect.Array; 38 import java.nio.charset.Charset; 39 import java.util.ArrayList; 40 import java.util.Arrays; 41 import java.util.Iterator; 42 import java.util.LinkedHashMap; 43 import java.util.Map; 44 import java.util.concurrent.Callable; 45 import java.util.concurrent.ExecutorService; 46 import java.util.concurrent.LinkedBlockingQueue; 47 import java.util.concurrent.ThreadPoolExecutor; 48 import java.util.concurrent.TimeUnit; 49  50 /** 51  ****************************************************************************** 52  * Taken from the JB source code, can be found in: 53  * libcore/luni/src/main/java/libcore/io/DiskLruCache.java 54  * or direct link: 55  * https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java 56  ****************************************************************************** 57  * 58  * A cache that uses a bounded amount of space on a filesystem. Each cache 59  * entry has a string key and a fixed number of values. Values are byte 60  * sequences, accessible as streams or files. Each value must be between {@code 61  * 0} and {@code Integer.MAX_VALUE} bytes in length. 62  * 63  * <p>The cache stores its data in a directory on the filesystem. This 64  * directory must be exclusive to the cache; the cache may delete or overwrite 65  * files from its directory. It is an error for multiple processes to use the 66  * same cache directory at the same time. 67  * 68  * <p>This cache limits the number of bytes that it will store on the 69  * filesystem. When the number of stored bytes exceeds the limit, the cache will 70  * remove entries in the background until the limit is satisfied. The limit is 71  * not strict: the cache may temporarily exceed it while waiting for files to be 72  * deleted. The limit does not include filesystem overhead or the cache 73  * journal so space-sensitive applications should set a conservative limit. 74  * 75  * <p>Clients call {@link #edit} to create or update the values of an entry. An 76  * entry may have only one editor at one time; if a value is not available to be 77  * edited then {@link #edit} will return null. 78  * <ul> 79  *     <li>When an entry is being <strong>created</strong> it is necessary to 80  *         supply a full set of values; the empty value should be used as a 81  *         placeholder if necessary. 82  *     <li>When an entry is being <strong>edited</strong>, it is not necessary 83  *         to supply data for every value; values default to their previous 84  *         value. 85  * </ul> 86  * Every {@link #edit} call must be matched by a call to {@link Editor#commit} 87  * or {@link Editor#abort}. Committing is atomic: a read observes the full set 88  * of values as they were before or after the commit, but never a mix of values. 89  * 90  * <p>Clients call {@link #get} to read a snapshot of an entry. The read will 91  * observe the value at the time that {@link #get} was called. Updates and 92  * removals after the call do not impact ongoing reads. 93  * 94  * <p>This class is tolerant of some I/O errors. If files are missing from the 95  * filesystem, the corresponding entries will be dropped from the cache. If 96  * an error occurs while writing a cache value, the edit will fail silently. 97  * Callers should handle other problems by catching {@code IOException} and 98  * responding appropriately. 99  */100 public final class DiskLruCache implements Closeable {101     static final String JOURNAL_FILE = "journal";102     static final String JOURNAL_FILE_TMP = "journal.tmp";103     static final String MAGIC = "libcore.io.DiskLruCache";104     static final String VERSION_1 = "1";105     static final long ANY_SEQUENCE_NUMBER = -1;106     private static final String CLEAN = "CLEAN";107     private static final String DIRTY = "DIRTY";108     private static final String REMOVE = "REMOVE";109     private static final String READ = "READ";110 111     private static final Charset UTF_8 = Charset.forName("UTF-8");112     private static final int IO_BUFFER_SIZE = 8 * 1024;113 114     /*115      * This cache uses a journal file named "journal". A typical journal file116      * looks like this:117      *     libcore.io.DiskLruCache118      *     1119      *     100120      *     2121      *122      *     CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054123      *     DIRTY 335c4c6028171cfddfbaae1a9c313c52124      *     CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342125      *     REMOVE 335c4c6028171cfddfbaae1a9c313c52126      *     DIRTY 1ab96a171faeeee38496d8b330771a7a127      *     CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234128      *     READ 335c4c6028171cfddfbaae1a9c313c52129      *     READ 3400330d1dfc7f3f7f4b8d4d803dfcf6130      *131      * The first five lines of the journal form its header. They are the132      * constant string "libcore.io.DiskLruCache", the disk cache's version,133      * the application's version, the value count, and a blank line.134      *135      * Each of the subsequent lines in the file is a record of the state of a136      * cache entry. Each line contains space-separated values: a state, a key,137      * and optional state-specific values.138      *   o DIRTY lines track that an entry is actively being created or updated.139      *     Every successful DIRTY action should be followed by a CLEAN or REMOVE140      *     action. DIRTY lines without a matching CLEAN or REMOVE indicate that141      *     temporary files may need to be deleted.142      *   o CLEAN lines track a cache entry that has been successfully published143      *     and may be read. A publish line is followed by the lengths of each of144      *     its values.145      *   o READ lines track accesses for LRU.146      *   o REMOVE lines track entries that have been deleted.147      *148      * The journal file is appended to as cache Operations occur. The journal may149      * occasionally be compacted by dropping redundant lines. A temporary file named150      * "journal.tmp" will be used during compaction; that file should be deleted if151      * it exists when the cache is opened.152      */153 154     private final File directory;155     private final File journalFile;156     private final File journalFileTmp;157     private final int appVersion;158     private final long maxSize;159     private final int valueCount;160     private long size = 0;161     private Writer journalWriter;162     private final LinkedHashMap<String, Entry> lruEntries163             = new LinkedHashMap<String, Entry>(0, 0.75f, true);164     private int redundantOpCount;165 166     /**167      * To differentiate between old and current snapshots, each entry is given168      * a sequence number each time an edit is committed. A snapshot is stale if169      * its sequence number is not equal to its entry's sequence number.170      */171     private long nextSequenceNumber = 0;172 173     /* From java.util.Arrays */174     @SuppressWarnings("unchecked")175     private static <T> T[] copyOfRange(T[] original, int start, int end) {176         final int originalLength = original.length; // For exception priority compatibility.177         if (start > end) {178             throw new IllegalArgumentException();179         }180         if (start < 0 || start > originalLength) {181             throw new ArrayIndexOutOfBoundsException();182         }183         final int resultLength = end - start;184         final int copyLength = Math.min(resultLength, originalLength - start);185         final T[] result = (T[]) Array186                 .newInstance(original.getClass().getComponentType(), resultLength);187         System.arraycopy(original, start, result, 0, copyLength);188         return result;189     }190 191     /**192      * Returns the remainder of 'reader' as a string, closing it when done.193      */194     public static String readFully(Reader reader) throws IOException {195         try {196             StringWriter writer = new StringWriter();197             char[] buffer = new char[1024];198             int count;199             while ((count = reader.read(buffer)) != -1) {200                 writer.write(buffer, 0, count);201             }202             return writer.toString();203         } finally {204             reader.close();205         }206     }207 208     /**209      * Returns the ASCII characters up to but not including the next "\r\n", or210      * "\n".211      *212      * @throws java.io.EOFException if the stream is exhausted before the next newline213      *     character.214      */215     public static String readAsciiLine(InputStream in) throws IOException {216         // TODO: support UTF-8 here instead217 218         StringBuilder result = new StringBuilder(80);219         while (true) {220             int c = in.read();221             if (c == -1) {222                 throw new EOFException();223             } else if (c == '\n') {224                 break;225             }226 227             result.append((char) c);228         }229         int length = result.length();230         if (length > 0 && result.charAt(length - 1) == '\r') {231             result.setLength(length - 1);232         }233         return result.toString();234     }235 236     /**237      * Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null.238      */239     public static void closeQuietly(Closeable closeable) {240         if (closeable != null) {241             try {242                 closeable.close();243             } catch (RuntimeException rethrown) {244                 throw rethrown;245             } catch (Exception ignored) {246             }247         }248     }249 250     /**251      * Recursively delete everything in {@code dir}.252      */253     // TODO: this should specify paths as Strings rather than as Files254     public static void deleteContents(File dir) throws IOException {255         File[] files = dir.listFiles();256         if (files == null) {257             throw new IllegalArgumentException("not a directory: " + dir);258         }259         for (File file : files) {260             if (file.isDirectory()) {261                 deleteContents(file);262             }263             if (!file.delete()) {264                 throw new IOException("failed to delete file: " + file);265             }266         }267     }268 269     /** This cache uses a single background thread to evict entries. */270     private final ExecutorService executorService = new ThreadPoolExecutor(0, 1,271             60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());272     private final Callable<Void> cleanupCallable = new Callable<Void>() {273         @Override public Void call() throws Exception {274             synchronized (DiskLruCache.this) {275                 if (journalWriter == null) {276                     return null; // closed277                 }278                 trimToSize();279                 if (journalRebuildRequired()) {280                     rebuildJournal();281                     redundantOpCount = 0;282                 }283             }284             return null;285         }286     };287 288     private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {289         this.directory = directory;290         this.appVersion = appVersion;291         this.journalFile = new File(directory, JOURNAL_FILE);292         this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);293         this.valueCount = valueCount;294         this.maxSize = maxSize;295     }296 297     /**298      * Opens the cache in {@code directory}, creating a cache if none exists299      * there.300      *301      * @param directory a writable directory302      * @param appVersion303      * @param valueCount the number of values per cache entry. Must be positive.304      * @param maxSize the maximum number of bytes this cache should use to store305      * @throws java.io.IOException if reading or writing the cache directory fails306      */307     public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)308             throws IOException {309         if (maxSize <= 0) {310             throw new IllegalArgumentException("maxSize <= 0");311         }312         if (valueCount <= 0) {313             throw new IllegalArgumentException("valueCount <= 0");314         }315 316         // prefer to pick up where we left off317         DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);318         if (cache.journalFile.exists()) {319             try {320                 cache.readJournal();321                 cache.processJournal();322                 cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true),323                         IO_BUFFER_SIZE);324                 return cache;325             } catch (IOException journalIsCorrupt) {326 //                System.logW("DiskLruCache " + directory + " is corrupt: "327 //                        + journalIsCorrupt.getMessage() + ", removing");328                 cache.delete();329             }330         }331 332         // create a new empty cache333         directory.mkdirs();334         cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);335         cache.rebuildJournal();336         return cache;337     }338 339     private void readJournal() throws IOException {340         InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE);341         try {342             String magic = readAsciiLine(in);343             String version = readAsciiLine(in);344             String appVersionString = readAsciiLine(in);345             String valueCountString = readAsciiLine(in);346             String blank = readAsciiLine(in);347             if (!MAGIC.equals(magic)348                     || !VERSION_1.equals(version)349                     || !Integer.toString(appVersion).equals(appVersionString)350                     || !Integer.toString(valueCount).equals(valueCountString)351                     || !"".equals(blank)) {352                 throw new IOException("unexpected journal header: ["353                         + magic + ", " + version + ", " + valueCountString + ", " + blank + "]");354             }355 356             while (true) {357                 try {358                     readJournalLine(readAsciiLine(in));359                 } catch (EOFException endOfJournal) {360                     break;361                 }362             }363         } finally {364             closeQuietly(in);365         }366     }367 368     private void readJournalLine(String line) throws IOException {369         String[] parts = line.split(" ");370         if (parts.length < 2) {371             throw new IOException("unexpected journal line: " + line);372         }373 374         String key = parts[1];375         if (parts[0].equals(REMOVE) && parts.length == 2) {376             lruEntries.remove(key);377             return;378         }379 380         Entry entry = lruEntries.get(key);381         if (entry == null) {382             entry = new Entry(key);383             lruEntries.put(key, entry);384         }385 386         if (parts[0].equals(CLEAN) && parts.length == 2 + valueCount) {387             entry.readable = true;388             entry.currentEditor = null;389             entry.setLengths(copyOfRange(parts, 2, parts.length));390         } else if (parts[0].equals(DIRTY) && parts.length == 2) {391             entry.currentEditor = new Editor(entry);392         } else if (parts[0].equals(READ) && parts.length == 2) {393             // this work was already done by calling lruEntries.get()394         } else {395             throw new IOException("unexpected journal line: " + line);396         }397     }398 399     /**400      * Computes the initial size and collects garbage as a part of opening the401      * cache. Dirty entries are assumed to be inconsistent and will be deleted.402      */403     private void processJournal() throws IOException {404         deleteIfExists(journalFileTmp);405         for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) {406             Entry entry = i.next();407             if (entry.currentEditor == null) {408                 for (int t = 0; t < valueCount; t++) {409                     size += entry.lengths[t];410                 }411             } else {412                 entry.currentEditor = null;413                 for (int t = 0; t < valueCount; t++) {414                     deleteIfExists(entry.getCleanFile(t));415                     deleteIfExists(entry.getDirtyFile(t));416                 }417                 i.remove();418             }419         }420     }421 422     /**423      * Creates a new journal that omits redundant information. This replaces the424      * current journal if it exists.425      */426     private synchronized void rebuildJournal() throws IOException {427         if (journalWriter != null) {428             journalWriter.close();429         }430 431         Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE);432         writer.write(MAGIC);433         writer.write("\n");434         writer.write(VERSION_1);435         writer.write("\n");436         writer.write(Integer.toString(appVersion));437         writer.write("\n");438         writer.write(Integer.toString(valueCount));439         writer.write("\n");440         writer.write("\n");441 442         for (Entry entry : lruEntries.values()) {443             if (entry.currentEditor != null) {444                 writer.write(DIRTY + ' ' + entry.key + '\n');445             } else {446                 writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');447             }448         }449 450         writer.close();451         journalFileTmp.renameTo(journalFile);452         journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE);453     }454 455     private static void deleteIfExists(File file) throws IOException {456 //        try {457 //            Libcore.os.remove(file.getPath());458 //        } catch (ErrnoException errnoException) {459 //            if (errnoException.errno != OsConstants.ENOENT) {460 //                throw errnoException.rethrowAsIOException();461 //            }462 //        }463         if (file.exists() && !file.delete()) {464             throw new IOException();465         }466     }467 468     /**469      * Returns a snapshot of the entry named {@code key}, or null if it doesn't470      * exist is not currently readable. If a value is returned, it is moved to471      * the head of the LRU queue.472      */473     public synchronized Snapshot get(String key) throws IOException {474         checkNotClosed();475         validateKey(key);476         Entry entry = lruEntries.get(key);477         if (entry == null) {478             return null;479         }480 481         if (!entry.readable) {482             return null;483         }484 485         /*486          * Open all streams eagerly to guarantee that we see a single published487          * snapshot. If we opened streams lazily then the streams could come488          * from different edits.489          */490         InputStream[] ins = new InputStream[valueCount];491         try {492             for (int i = 0; i < valueCount; i++) {493                 ins[i] = new FileInputStream(entry.getCleanFile(i));494             }495         } catch (FileNotFoundException e) {496             // a file must have been deleted manually!497             return null;498         }499 500         redundantOpCount++;501         journalWriter.append(READ + ' ' + key + '\n');502         if (journalRebuildRequired()) {503             executorService.submit(cleanupCallable);504         }505 506         return new Snapshot(key, entry.sequenceNumber, ins);507     }508 509     /**510      * Returns an editor for the entry named {@code key}, or null if another511      * edit is in progress.512      */513     public Editor edit(String key) throws IOException {514         return edit(key, ANY_SEQUENCE_NUMBER);515     }516 517     private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {518         checkNotClosed();519         validateKey(key);520         Entry entry = lruEntries.get(key);521         if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER522                 && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {523             return null; // snapshot is stale524         }525         if (entry == null) {526             entry = new Entry(key);527             lruEntries.put(key, entry);528         } else if (entry.currentEditor != null) {529             return null; // another edit is in progress530         }531 532         Editor editor = new Editor(entry);533         entry.currentEditor = editor;534 535         // flush the journal before creating files to prevent file leaks536         journalWriter.write(DIRTY + ' ' + key + '\n');537         journalWriter.flush();538         return editor;539     }540 541     /**542      * Returns the directory where this cache stores its data.543      */544     public File getDirectory() {545         return directory;546     }547 548     /**549      * Returns the maximum number of bytes that this cache should use to store550      * its data.551      */552     public long maxSize() {553         return maxSize;554     }555 556     /**557      * Returns the number of bytes currently being used to store the values in558      * this cache. This may be greater than the max size if a background559      * deletion is pending.560      */561     public synchronized long size() {562         return size;563     }564 565     private synchronized void completeEdit(Editor editor, boolean success) throws IOException {566         Entry entry = editor.entry;567         if (entry.currentEditor != editor) {568             throw new IllegalStateException();569         }570 571         // if this edit is creating the entry for the first time, every index must have a value572         if (success && !entry.readable) {573             for (int i = 0; i < valueCount; i++) {574                 if (!entry.getDirtyFile(i).exists()) {575                     editor.abort();576                     throw new IllegalStateException("edit didn't create file " + i);577                 }578             }579         }580 581         for (int i = 0; i < valueCount; i++) {582             File dirty = entry.getDirtyFile(i);583             if (success) {584                 if (dirty.exists()) {585                     File clean = entry.getCleanFile(i);586                     dirty.renameTo(clean);587                     long oldLength = entry.lengths[i];588                     long newLength = clean.length();589                     entry.lengths[i] = newLength;590                     size = size - oldLength + newLength;591                 }592             } else {593                 deleteIfExists(dirty);594             }595         }596 597         redundantOpCount++;598         entry.currentEditor = null;599         if (entry.readable | success) {600             entry.readable = true;601             journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');602             if (success) {603                 entry.sequenceNumber = nextSequenceNumber++;604             }605         } else {606             lruEntries.remove(entry.key);607             journalWriter.write(REMOVE + ' ' + entry.key + '\n');608         }609 610         if (size > maxSize || journalRebuildRequired()) {611             executorService.submit(cleanupCallable);612         }613     }614 615     /**616      * We only rebuild the journal when it will halve the size of the journal617      * and eliminate at least 2000 ops.618      */619     private boolean journalRebuildRequired() {620         final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;621         return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD622                 && redundantOpCount >= lruEntries.size();623     }624 625     /**626      * Drops the entry for {@code key} if it exists and can be removed. Entries627      * actively being edited cannot be removed.628      *629      * @return true if an entry was removed.630      */631     public synchronized boolean remove(String key) throws IOException {632         checkNotClosed();633         validateKey(key);634         Entry entry = lruEntries.get(key);635         if (entry == null || entry.currentEditor != null) {636             return false;637         }638 639         for (int i = 0; i < valueCount; i++) {640             File file = entry.getCleanFile(i);641             if (!file.delete()) {642                 throw new IOException("failed to delete " + file);643             }644             size -= entry.lengths[i];645             entry.lengths[i] = 0;646         }647 648         redundantOpCount++;649         journalWriter.append(REMOVE + ' ' + key + '\n');650         lruEntries.remove(key);651 652         if (journalRebuildRequired()) {653             executorService.submit(cleanupCallable);654         }655 656         return true;657     }658 659     /**660      * Returns true if this cache has been closed.661      */662     public boolean isClosed() {663         return journalWriter == null;664     }665 666     private void checkNotClosed() {667         if (journalWriter == null) {668             throw new IllegalStateException("cache is closed");669         }670     }671 672     /**673      * Force buffered operations to the filesystem.674      */675     public synchronized void flush() throws IOException {676         checkNotClosed();677         trimToSize();678         journalWriter.flush();679     }680 681     /**682      * Closes this cache. Stored values will remain on the filesystem.683      */684     public synchronized void close() throws IOException {685         if (journalWriter == null) {686             return; // already closed687         }688         for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {689             if (entry.currentEditor != null) {690                 entry.currentEditor.abort();691             }692         }693         trimToS