探究图片加载的实现方式
2016-03-19 14:19
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即使在项目不会使用自定义的方法来记载图片(往往使用第三方类库),但是探究图片加载的过程,对程序员能力的提升还是很有意义的。
参考了Android官方学习文档
展示一下效果图
2.在SD卡上查找,如果命中则显示。否则,进行下一步;
3.发送网络请求,将下载图片,保存到内存、SD卡,显示图片。
2.加载图片
3.下面看一下工作线程BitmapWorkerTask
这就是大名鼎鼎的DiskLruCache
这个是我的主要拙作
测试的图片内容类(这是某个csdn大牛的贡献,找不到名字了,在此谢过了)
图片展示的adapter
这是测试的MainActivity
不要忘记添加权限哦
参考了Android官方学习文档
展示一下效果图
大体描述一下图片加载的流程
1.在内存中查找,如果命中则显示。否则,进行下一步;2.在SD卡上查找,如果命中则显示。否则,进行下一步;
3.发送网络请求,将下载图片,保存到内存、SD卡,显示图片。
参照代码进行解释说明
1.首先实例化用于图片缓存的内存和sd卡(这里使用了DiskLruCache)public void init(Context applicationContext) { this.mAppContext = applicationContext; if (instance == null) { final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024); final int cacheSize = maxMemory / 8; //使用安卓系统分配给APP 1/8的内存作为图片缓存的空间 mMemoryCache = new LruCache<String, Bitmap>(cacheSize) { @Override protected int sizeOf(String key, Bitmap bitmap) { return bitmap.getRowBytes() * bitmap.getHeight()/1024+1; } }; //实例化SD卡缓存空间 File cacheDir = getDiskCacheDir(mAppContext, DISK_CACHE_SUBDIR); new InitDiskCacheTask().execute(cacheDir); } instance = this; } class InitDiskCacheTask extends AsyncTask<File, Void, Void> { @Override protected Void doInBackground(File... params) { synchronized (mDiskCacheLock) { File cacheDir = params[0]; try { //下面是DiskLruCache的逻辑。mDiskCacheLock:这是一个SD缓存的锁,保证仅仅只有一个线程在操作SD卡。 //当实例化SD缓存后,调用notifyAll,唤醒其他因为等待mDiskCacheLock而阻塞的线程 mDiskLruCache = DiskLruCache.open(cacheDir, getAppVersion(mAppContext), 1, DISK_CACHE_SIZE); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } mDiskCacheStarting = false; // Finished initialization mDiskCacheLock.notifyAll(); // Wake any waiting threads } return null; } }
2.加载图片
private void loadBitmap(ImageView imageView, String imageUrl, Bitmap placeHolder) { //1.判断图片的内存缓存中是否存在,如果存在直接加载 final Bitmap bitmap = getBitmapFromMemCache(imageUrl); if (bitmap != null) { imageView.setImageBitmap(bitmap); } else { //2.判断该图片是否downloading,如果是,取消后续操作。你可能会问,不是还没有判断sd卡吗?由于将sd卡上的图片解码到内存是比较“麻烦的”,将它放到工作线程里面了。 if (cancelPotentialWork(imageUrl, imageView)) { //这是一个“循环三角”,任何一个都有路径找到其他两个 //BitmapWorkerTask->ImageView final BitmapWorkerTask task = new BitmapWorkerTask(imageView); //AsyncDrawable->BitmapWorkerTask final AsyncDrawable asyncDrawable = new AsyncDrawable( mAppContext.getResources(), placeHolder, task); //ImageView->AsyncDrawable imageView.setImageDrawable(asyncDrawable); //如果安卓系统在3.0以上,允许task并执行,并发数为5;否则只能顺序执行 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, imageUrl); } else { task.execute(imageUrl); } } } }
3.下面看一下工作线程BitmapWorkerTask
class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> { private WeakReference<ImageView> imageViewReference; private String imageUrl; public BitmapWorkerTask(ImageView imageView) { //这里使用了弱引用,当组件不存在了(eg.页面已经销毁了),不会导致内存泄露 imageViewReference = new WeakReference<ImageView>(imageView); } @Override protected Bitmap doInBackground(String... params) { imageUrl = params[0]; //这里就是解码sd卡上的图片了 Bitmap bitmap = getBitmapFromDiskCache(imageUrl, , ); if (bitmap == null) { bitmap = downloadBitmap(imageUrl); } // 将图片保存到内存缓存和sd卡上 if (bitmap != null) { addBitmapToCache(imageUrl, bitmap); } return bitmap; } @Override protected void onPostExecute(Bitmap bitmap) { //防止图片下载失败,导致APP崩溃 if (bitmap != null && imageViewReference != null) { ImageView imageView = imageViewReference.get(); //防止该页面已经关闭 if (imageView != null) { imageView.setImageBitmap(bitmap); } } }
附上完整版代码用于参考
由于图片原始路径中可能包含特殊字符不能用于标志文件名,用下面的工具类,对文件路径进行一下hash运行package libcore.io; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class MD5Utils { public static String hashKeyForDisk(String key) { String cacheKey; try { final MessageDigest mDigest = MessageDigest.getInstance("MD5"); mDigest.update(key.getBytes()); cacheKey = bytesToHexString(mDigest.digest()); } catch (NoSuchAlgorithmException e) { cacheKey = String.valueOf(key.hashCode()); } return cacheKey; } private static String bytesToHexString(byte[] bytes) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < bytes.length; i++) { String hex = Integer.toHexString(0xFF & bytes[i]); if (hex.length() == 1) { sb.append('0'); } sb.append(hex); } return sb.toString(); } }
这就是大名鼎鼎的DiskLruCache
/* * Copyright (C) 2011 The Android Open Source Project * * 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 libcore.io; import java.io.BufferedInputStream; import java.io.BufferedWriter; import java.io.Closeable; import java.io.EOFException; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.FileWriter; import java.io.FilterOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.io.OutputStreamWriter; import java.io.Reader; import java.io.StringWriter; import java.io.Writer; import java.lang.reflect.Array; import java.nio.charset.Charset; import java.util.ArrayList; import java.util.Arrays; import java.util.Iterator; import java.util.LinkedHashMap; import java.util.Map; import java.util.concurrent.Callable; import java.util.concurrent.ExecutorService; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; /** ****************************************************************************** * Taken from the JB source code, can be found in: * libcore/luni/src/main/java/libcore/io/DiskLruCache.java * or direct link: * https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java ****************************************************************************** * * A cache that uses a bounded amount of space on a filesystem. Each cache * entry has a string key and a fixed number of values. Values are byte * sequences, accessible as streams or files. Each value must be between {@code * 0} and {@code Integer.MAX_VALUE} bytes in length. * * <p>The cache stores its data in a directory on the filesystem. This * directory must be exclusive to the cache; the cache may delete or overwrite * files from its directory. It is an error for multiple processes to use the * same cache directory at the same time. * * <p>This cache limits the number of bytes that it will store on the * filesystem. When the number of stored bytes exceeds the limit, the cache will * remove entries in the background until the limit is satisfied. The limit is * not strict: the cache may temporarily exceed it while waiting for files to be * deleted. The limit does not include filesystem overhead or the cache * journal so space-sensitive applications should set a conservative limit. * * <p>Clients call {@link #edit} to create or update the values of an entry. An * entry may have only one editor at one time; if a value is not available to be * edited then {@link #edit} will return null. * <ul> * <li>When an entry is being <strong>created</strong> it is necessary to * supply a full set of values; the empty value should be used as a * placeholder if necessary. * <li>When an entry is being <strong>edited</strong>, it is not necessary * to supply data for every value; values default to their previous * value. * </ul> * Every {@link #edit} call must be matched by a call to {@link Editor#commit} * or {@link Editor#abort}. Committing is atomic: a read observes the full set * of values as they were before or after the commit, but never a mix of values. * * <p>Clients call {@link #get} to read a snapshot of an entry. The read will * observe the value at the time that {@link #get} was called. Updates and * removals after the call do not impact ongoing reads. * * <p>This class is tolerant of some I/O errors. If files are missing from the * filesystem, the corresponding entries will be dropped from the cache. If * an error occurs while writing a cache value, the edit will fail silently. * Callers should handle other problems by catching {@code IOException} and * responding appropriately. */ public final class DiskLruCache implements Closeable { static final String JOURNAL_FILE = "journal"; static final String JOURNAL_FILE_TMP = "journal.tmp"; static final String MAGIC = "libcore.io.DiskLruCache"; static final String VERSION_1 = "1"; static final long ANY_SEQUENCE_NUMBER = -1; private static final String CLEAN = "CLEAN"; private static final String DIRTY = "DIRTY"; private static final String REMOVE = "REMOVE"; private static final String READ = "READ"; private static final Charset UTF_8 = Charset.forName("UTF-8"); private static final int IO_BUFFER_SIZE = 8 * 1024; /* * This cache uses a journal file named "journal". A typical journal file * looks like this: * libcore.io.DiskLruCache * 1 * 100 * 2 * * CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054 * DIRTY 335c4c6028171cfddfbaae1a9c313c52 * CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342 * REMOVE 335c4c6028171cfddfbaae1a9c313c52 * DIRTY 1ab96a171faeeee38496d8b330771a7a * CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234 * READ 335c4c6028171cfddfbaae1a9c313c52 * READ 3400330d1dfc7f3f7f4b8d4d803dfcf6 * * The first five lines of the journal form its header. They are the * constant string "libcore.io.DiskLruCache", the disk cache's version, * the application's version, the value count, and a blank line. * * Each of the subsequent lines in the file is a record of the state of a * cache entry. Each line contains space-separated values: a state, a key, * and optional state-specific values. * o DIRTY lines track that an entry is actively being created or updated. * Every successful DIRTY action should be followed by a CLEAN or REMOVE * action. DIRTY lines without a matching CLEAN or REMOVE indicate that * temporary files may need to be deleted. * o CLEAN lines track a cache entry that has been successfully published * and may be read. A publish line is followed by the lengths of each of * its values. * o READ lines track accesses for LRU. * o REMOVE lines track entries that have been deleted. * * The journal file is appended to as cache operations occur. The journal may * occasionally be compacted by dropping redundant lines. A temporary file named * "journal.tmp" will be used during compaction; that file should be deleted if * it exists when the cache is opened. */ private final File directory; private final File journalFile; private final File journalFileTmp; private final int appVersion; private final long maxSize; private final int valueCount; private long size = 0; private Writer journalWriter; private final LinkedHashMap<String, Entry> lruEntries = new LinkedHashMap<String, Entry>(0, 0.75f, true); private int redundantOpCount; /** * To differentiate between old and current snapshots, each entry is given * a sequence number each time an edit is committed. A snapshot is stale if * its sequence number is not equal to its entry's sequence number. */ private long nextSequenceNumber = 0; /* From java.util.Arrays */ @SuppressWarnings("unchecked") private static <T> T[] copyOfRange(T[] original, int start, int end) { final int originalLength = original.length; // For exception priority compatibility. if (start > end) { throw new IllegalArgumentException(); } if (start < 0 || start > originalLength) { throw new ArrayIndexOutOfBoundsException(); } final int resultLength = end - start; final int copyLength = Math.min(resultLength, originalLength - start); final T[] result = (T[]) Array .newInstance(original.getClass().getComponentType(), resultLength); System.arraycopy(original, start, result, 0, copyLength); return result; } /** * Returns the remainder of 'reader' as a string, closing it when done. */ public static String readFully(Reader reader) throws IOException { try { StringWriter writer = new StringWriter(); char[] buffer = new char[1024]; int count; while ((count = reader.read(buffer)) != -1) { writer.write(buffer, 0, count); } return writer.toString(); } finally { reader.close(); } } /** * Returns the ASCII characters up to but not including the next "\r\n", or * "\n". * * @throws java.io.EOFException if the stream is exhausted before the next newline * character. */ public static String readAsciiLine(InputStream in) throws IOException { // TODO: support UTF-8 here instead StringBuilder result = new StringBuilder(80); while (true) { int c = in.read(); if (c == -1) { throw new EOFException(); } else if (c == '\n') { break; } result.append((char) c); } int length = result.length(); if (length > 0 && result.charAt(length - 1) == '\r') { result.setLength(length - 1); } return result.toString(); } /** * Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null. */ public static void closeQuietly(Closeable closeable) { if (closeable != null) { try { closeable.close(); } catch (RuntimeException rethrown) { throw rethrown; } catch (Exception ignored) { } } } /** * Recursively delete everything in {@code dir}. */ // TODO: this should specify paths as Strings rather than as Files public static void deleteContents(File dir) throws IOException { File[] files = dir.listFiles(); if (files == null) { throw new IllegalArgumentException("not a directory: " + dir); } for (File file : files) { if (file.isDirectory()) { deleteContents(file); } if (!file.delete()) { throw new IOException("failed to delete file: " + file); } } } /** This cache uses a single background thread to evict entries. */ private final ExecutorService executorService = new ThreadPoolExecutor(0, 1, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>()); private final Callable<Void> cleanupCallable = new Callable<Void>() { @Override public Void call() throws Exception { synchronized (DiskLruCache.this) { if (journalWriter == null) { return null; // closed } trimToSize(); if (journalRebuildRequired()) { rebuildJournal(); redundantOpCount = 0; } } return null; } }; private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) { this.directory = directory; this.appVersion = appVersion; this.journalFile = new File(directory, JOURNAL_FILE); this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP); this.valueCount = valueCount; this.maxSize = maxSize; } /** * Opens the cache in {@code directory}, creating a cache if none exists * there. * * @param directory a writable directory * @param appVersion * @param valueCount the number of values per cache entry. Must be positive. * @param maxSize the maximum number of bytes this cache should use to store * @throws java.io.IOException if reading or writing the cache directory fails */ public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize) throws IOException { if (maxSize <= 0) { throw new IllegalArgumentException("maxSize <= 0"); } if (valueCount <= 0) { throw new IllegalArgumentException("valueCount <= 0"); } // prefer to pick up where we left off DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize); if (cache.journalFile.exists()) { try { cache.readJournal(); cache.processJournal(); cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true), IO_BUFFER_SIZE); return cache; } catch (IOException journalIsCorrupt) { // System.logW("DiskLruCache " + directory + " is corrupt: " // + journalIsCorrupt.getMessage() + ", removing"); cache.delete(); } } // create a new empty cache directory.mkdirs(); cache = new DiskLruCache(directory, appVersion, valueCount, maxSize); cache.rebuildJournal(); return cache; } private void readJournal() throws IOException { InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE); try { String magic = readAsciiLine(in); String version = readAsciiLine(in); String appVersionString = readAsciiLine(in); String valueCountString = readAsciiLine(in); String blank = readAsciiLine(in); if (!MAGIC.equals(magic) || !VERSION_1.equals(version) || !Integer.toString(appVersion).equals(appVersionString) || !Integer.toString(valueCount).equals(valueCountString) || !"".equals(blank)) { throw new IOException("unexpected journal header: [" + magic + ", " + version + ", " + valueCountString + ", " + blank + "]"); } while (true) { try { readJournalLine(readAsciiLine(in)); } catch (EOFException endOfJournal) { break; } } } finally { closeQuietly(in); } } private void readJournalLine(String line) throws IOException { String[] parts = line.split(" "); if (parts.length < 2) { throw new IOException("unexpected journal line: " + line); } String key = parts[1]; if (parts[0].equals(REMOVE) && parts.length == 2) { lruEntries.remove(key); return; } Entry entry = lruEntries.get(key); if (entry == null) { entry = new Entry(key); lruEntries.put(key, entry); } if (parts[0].equals(CLEAN) && parts.length == 2 + valueCount) { entry.readable = true; entry.currentEditor = null; entry.setLengths(copyOfRange(parts, 2, parts.length)); } else if (parts[0].equals(DIRTY) && parts.length == 2) { entry.currentEditor = new Editor(entry); } else if (parts[0].equals(READ) && parts.length == 2) { // this work was already done by calling lruEntries.get() } else { throw new IOException("unexpected journal line: " + line); } } /** * Computes the initial size and collects garbage as a part of opening the * cache. Dirty entries are assumed to be inconsistent and will be deleted. */ private void processJournal() throws IOException { deleteIfExists(journalFileTmp); for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) { Entry entry = i.next(); if (entry.currentEditor == null) { for (int t = 0; t < valueCount; t++) { size += entry.lengths[t]; } } else { entry.currentEditor = null; for (int t = 0; t < valueCount; t++) { deleteIfExists(entry.getCleanFile(t)); deleteIfExists(entry.getDirtyFile(t)); } i.remove(); } } } /** * Creates a new journal that omits redundant information. This replaces the * current journal if it exists. */ private synchronized void rebuildJournal() throws IOException { if (journalWriter != null) { journalWriter.close(); } Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE); writer.write(MAGIC); writer.write("\n"); writer.write(VERSION_1); writer.write("\n"); writer.write(Integer.toString(appVersion)); writer.write("\n"); writer.write(Integer.toString(valueCount)); writer.write("\n"); writer.write("\n"); for (Entry entry : lruEntries.values()) { if (entry.currentEditor != null) { writer.write(DIRTY + ' ' + entry.key + '\n'); } else { writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n'); } } writer.close(); journalFileTmp.renameTo(journalFile); journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE); } private static void deleteIfExists(File file) throws IOException { // try { // Libcore.os.remove(file.getPath()); // } catch (ErrnoException errnoException) { // if (errnoException.errno != OsConstants.ENOENT) { // throw errnoException.rethrowAsIOException(); // } // } if (file.exists() && !file.delete()) { throw new IOException(); } } /** * Returns a snapshot of the entry named {@code key}, or null if it doesn't * exist is not currently readable. If a value is returned, it is moved to * the head of the LRU queue. */ public synchronized Snapshot get(String key) throws IOException { checkNotClosed(); validateKey(key); Entry entry = lruEntries.get(key); if (entry == null) { return null; } if (!entry.readable) { return null; } /* * Open all streams eagerly to guarantee that we see a single published * snapshot. If we opened streams lazily then the streams could come * from different edits. */ InputStream[] ins = new InputStream[valueCount]; try { for (int i = 0; i < valueCount; i++) { ins[i] = new FileInputStream(entry.getCleanFile(i)); } } catch (FileNotFoundException e) { // a file must have been deleted manually! return null; } redundantOpCount++; journalWriter.append(READ + ' ' + key + '\n'); if (journalRebuildRequired()) { executorService.submit(cleanupCallable); } return new Snapshot(key, entry.sequenceNumber, ins); } /** * Returns an editor for the entry named {@code key}, or null if another * edit is in progress. */ public Editor edit(String key) throws IOException { return edit(key, ANY_SEQUENCE_NUMBER); } private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException { checkNotClosed(); validateKey(key); Entry entry = lruEntries.get(key); if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) { return null; // snapshot is stale } if (entry == null) { entry = new Entry(key); lruEntries.put(key, entry); } else if (entry.currentEditor != null) { return null; // another edit is in progress } Editor editor = new Editor(entry); entry.currentEditor = editor; // flush the journal before creating files to prevent file leaks journalWriter.write(DIRTY + ' ' + key + '\n'); journalWriter.flush(); return editor; } /** * Returns the directory where this cache stores its data. */ public File getDirectory() { return directory; } /** * Returns the maximum number of bytes that this cache should use to store * its data. */ public long maxSize() { return maxSize; } /** * Returns the number of bytes currently being used to store the values in * this cache. This may be greater than the max size if a background * deletion is pending. */ public synchronized long size() { return size; } private synchronized void completeEdit(Editor editor, boolean success) throws IOException { Entry entry = editor.entry; if (entry.currentEditor != editor) { throw new IllegalStateException(); } // if this edit is creating the entry for the first time, every index must have a value if (success && !entry.readable) { for (int i = 0; i < valueCount; i++) { if (!entry.getDirtyFile(i).exists()) { editor.abort(); throw new IllegalStateException("edit didn't create file " + i); } } } for (int i = 0; i < valueCount; i++) { File dirty = entry.getDirtyFile(i); if (success) { if (dirty.exists()) { File clean = entry.getCleanFile(i); dirty.renameTo(clean); long oldLength = entry.lengths[i]; long newLength = clean.length(); entry.lengths[i] = newLength; size = size - oldLength + newLength; } } else { deleteIfExists(dirty); } } redundantOpCount++; entry.currentEditor = null; if (entry.readable | success) { entry.readable = true; journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n'); if (success) { entry.sequenceNumber = nextSequenceNumber++; } } else { lruEntries.remove(entry.key); journalWriter.write(REMOVE + ' ' + entry.key + '\n'); } if (size > maxSize || journalRebuildRequired()) { executorService.submit(cleanupCallable); } } /** * We only rebuild the journal when it will halve the size of the journal * and eliminate at least 2000 ops. */ private boolean journalRebuildRequired() { final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000; return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD && redundantOpCount >= lruEntries.size(); } /** * Drops the entry for {@code key} if it exists and can be removed. Entries * actively being edited cannot be removed. * * @return true if an entry was removed. */ public synchronized boolean remove(String key) throws IOException { checkNotClosed(); validateKey(key); Entry entry = lruEntries.get(key); if (entry == null || entry.currentEditor != null) { return false; } for (int i = 0; i < valueCount; i++) { File file = entry.getCleanFile(i); if (!file.delete()) { throw new IOException("failed to delete " + file); } size -= entry.lengths[i]; entry.lengths[i] = 0; } redundantOpCount++; journalWriter.append(REMOVE + ' ' + key + '\n'); lruEntries.remove(key); if (journalRebuildRequired()) { executorService.submit(cleanupCallable); } return true; } /** * Returns true if this cache has been closed. */ public boolean isClosed() { return journalWriter == null; } private void checkNotClosed() { if (journalWriter == null) { throw new IllegalStateException("cache is closed"); } } /** * Force buffered operations to the filesystem. */ public synchronized void flush() throws IOException { checkNotClosed(); trimToSize(); journalWriter.flush(); } /** * Closes this cache. Stored values will remain on the filesystem. */ public synchronized void close() throws IOException { if (journalWriter == null) { return; // already closed } for (Entry entry : new ArrayList<Entry>(lruEntries.values())) { if (entry.currentEditor != null) { entry.currentEditor.abort(); } } trimToSize(); journalWriter.close(); journalWriter = null; } private void trimToSize() throws IOException { while (size > maxSize) { // Map.Entry<String, Entry> toEvict = lruEntries.eldest(); final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next(); remove(toEvict.getKey()); } } /** * Closes the cache and deletes all of its stored values. This will delete * all files in the cache directory including files that weren't created by * the cache. */ public void delete() throws IOException { close(); deleteContents(directory); } private void validateKey(String key) { if (key.contains(" ") || key.contains("\n") || key.contains("\r")) { throw new IllegalArgumentException( "keys must not contain spaces or newlines: \"" + key + "\""); } } private static String inputStreamToString(InputStream in) throws IOException { return readFully(new InputStreamReader(in, UTF_8)); } /** * A snapshot of the values for an entry. */ public final class Snapshot implements Closeable { private final String key; private final long sequenceNumber; private final InputStream[] ins; private Snapshot(String key, long sequenceNumber, InputStream[] ins) { this.key = key; this.sequenceNumber = sequenceNumber; this.ins = ins; } /** * Returns an editor for this snapshot's entry, or null if either the * entry has changed since this snapshot was created or if another edit * is in progress. */ public Editor edit() throws IOException { return DiskLruCache.this.edit(key, sequenceNumber); } /** * Returns the unbuffered stream with the value for {@code index}. */ public InputStream getInputStream(int index) { return ins[index]; } /** * Returns the string value for {@code index}. */ public String getString(int index) throws IOException { return inputStreamToString(getInputStream(index)); } @Override public void close() { for (InputStream in : ins) { closeQuietly(in); } } } /** * Edits the values for an entry. */ public final class Editor { private final Entry entry; private boolean hasErrors; private Editor(Entry entry) { this.entry = entry; } /** * Returns an unbuffered input stream to read the last committed value, * or null if no value has been committed. */ public InputStream newInputStream(int index) throws IOException { synchronized (DiskLruCache.this) { if (entry.currentEditor != this) { throw new IllegalStateException(); } if (!entry.readable) { return null; } return new FileInputStream(entry.getCleanFile(index)); } } /** * Returns the last committed value as a string, or null if no value * has been committed. */ public String getString(int index) throws IOException { InputStream in = newInputStream(index); return in != null ? inputStreamToString(in) : null; } /** * Returns a new unbuffered output stream to write the value at * {@code index}. If the underlying output stream encounters errors * when writing to the filesystem, this edit will be aborted when * {@link #commit} is called. The returned output stream does not throw * IOExceptions. */ public OutputStream newOutputStream(int index) throws IOException { synchronized (DiskLruCache.this) { if (entry.currentEditor != this) { throw new IllegalStateException(); } return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index))); } } /** * Sets the value at {@code index} to {@code value}. */ public void set(int index, String value) throws IOException { Writer writer = null; try { writer = new OutputStreamWriter(newOutputStream(index), UTF_8); writer.write(value); } finally { closeQuietly(writer); } } /** * Commits this edit so it is visible to readers. This releases the * edit lock so another edit may be started on the same key. */ public void commit() throws IOException { if (hasErrors) { completeEdit(this, false); remove(entry.key); // the previous entry is stale } else { completeEdit(this, true); } } /** * Aborts this edit. This releases the edit lock so another edit may be * started on the same key. */ public void abort() throws IOException { completeEdit(this, false); } private class FaultHidingOutputStream extends FilterOutputStream { private FaultHidingOutputStream(OutputStream out) { super(out); } @Override public void write(int oneByte) { try { out.write(oneByte); } catch (IOException e) { hasErrors = true; } } @Override public void write(byte[] buffer, int offset, int length) { try { out.write(buffer, offset, length); } catch (IOException e) { hasErrors = true; } } @Override public void close() { try { out.close(); } catch (IOException e) { hasErrors = true; } } @Override public void flush() { try { out.flush(); } catch (IOException e) { hasErrors = true; } } } } private final class Entry { private final String key; /** Lengths of this entry's files. */ private final long[] lengths; /** True if this entry has ever been published */ private boolean readable; /** The ongoing edit or null if this entry is not being edited. */ private Editor currentEditor; /** The sequence number of the most recently committed edit to this entry. */ private long sequenceNumber; private Entry(String key) { this.key = key; this.lengths = new long[valueCount]; } public String getLengths() throws IOException { StringBuilder result = new StringBuilder(); for (long size : lengths) { result.append(' ').append(size); } return result.toString(); } /** * Set lengths using decimal numbers like "10123". */ private void setLengths(String[] strings) throws IOException { if (strings.length != valueCount) { throw invalidLengths(strings); } try { for (int i = 0; i < strings.length; i++) { lengths[i] = Long.parseLong(strings[i]); } } catch (NumberFormatException e) { throw invalidLengths(strings); } } private IOException invalidLengths(String[] strings) throws IOException { throw new IOException("unexpected journal line: " + Arrays.toString(strings)); } public File getCleanFile(int i) { return new File(directory, key + "." + i); } public File getDirtyFile(int i) { return new File(directory, key + "." + i + ".tmp"); } } }
这个是我的主要拙作
package libcore.io; import java.io.File; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.lang.ref.WeakReference; import java.net.HttpURLConnection; import java.net.URL; import java.util.concurrent.atomic.AtomicInteger; import android.annotation.SuppressLint; import android.content.Context; import android.content.pm.PackageInfo; import android.content.pm.PackageManager.NameNotFoundException; import android.content.res.Resources; import android.graphics.Bitmap; import android.graphics.Bitmap.CompressFormat; import android.graphics.BitmapFactory; import android.graphics.drawable.BitmapDrawable; import android.graphics.drawable.Drawable; import android.os.AsyncTask; import android.os.Build; import android.os.Environment; import android.support.v4.util.LruCache; import android.text.TextUtils; import android.util.Log; import android.widget.ImageView; /** * @author Chuanhang.Gu * */ public class ImageLoadGCH { // TODO 用户测试并发数 private AtomicInteger currencyNum = new AtomicInteger(); private static ImageLoadGCH instance; private static LruCache<String, Bitmap> mMemoryCache; private static DiskLruCache mDiskLruCache = null; private final Object mDiskCacheLock = new Object(); private boolean mDiskCacheStarting = true; private Context mAppContext; private static final int DISK_CACHE_SIZE = 1024 * 1024 * 40; private static final String DISK_CACHE_SUBDIR = "thumbnails_gch"; private void init(Context applicationContext) { this.mAppContext = applicationContext; final int maxMemory = (int) (Runtime.getRuntime().maxMemory()); final int cacheSize = maxMemory / 8; mMemoryCache = new LruCache<String, Bitmap>(cacheSize) { @Override protected int sizeOf(String key, Bitmap bitmap) { return bitmap.getRowBytes() * bitmap.getHeight(); } }; File cacheDir = getDiskCacheDir(mAppContext, DISK_CACHE_SUBDIR); new InitDiskCacheTask().execute(cacheDir); } private ImageLoadGCH(Context appContext) { init(appContext); } public static synchronized ImageLoadGCH getInstance(Context appContext) { if (instance == null) { instance = new ImageLoadGCH(appContext); } return instance; } /** * 在onPause中调用,将保存到sd卡上的记录,同步到journal 文件上 */ public void flushSDJournal() { try { if (mDiskLruCache != null) { mDiskLruCache.flush(); } } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void loadImage(ImageView imageView, String imageUrl, int defaultResId) { Bitmap defaultBitmap = BitmapFactory.decodeResource( mAppContext.getResources(), defaultResId); loadBitmap(imageView, imageUrl, defaultBitmap); } @SuppressLint("NewApi") private File getDiskCacheDir(Context context, String uniqueName) { String cachePath = null; if (Environment.MEDIA_MOUNTED.equals(Environment .getExternalStorageState())) { cachePath = context.getExternalCacheDir().getPath(); } else { if (Build.VERSION.SDK_INT >= 9) { if (!Environment.isExternalStorageRemovable()) { cachePath = context.getExternalCacheDir().getPath(); } else { cachePath = context.getCacheDir().getPath(); } } } return new File(cachePath + File.separator + uniqueName); } class InitDiskCacheTask extends AsyncTask<File, Void, Void> { @Override protected Void doInBackground(File... params) { synchronized (mDiskCacheLock) { File cacheDir = params[0]; try { mDiskLruCache = DiskLruCache.open(cacheDir, getAppVersion(mAppContext), 1, DISK_CACHE_SIZE); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } mDiskCacheStarting = false; // Finished initialization mDiskCacheLock.notifyAll(); // Wake any waiting threads } return null; } } private int getAppVersion(Context context) { try { PackageInfo info = context.getPackageManager().getPackageInfo( context.getPackageName(), 0); return info.versionCode; } catch (NameNotFoundException e) { e.printStackTrace(); } return 1; } public Bitmap getBitmapFromMemCache(String imageUrl) { return mMemoryCache.get(imageUrl); } static class AsyncDrawable extends BitmapDrawable { private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference; public AsyncDrawable(Resources res, Bitmap bitmap, BitmapWorkerTask bitmapWorkerTask) { super(res, bitmap); bitmapWorkerTaskReference = new WeakReference<BitmapWorkerTask>( bitmapWorkerTask); } public BitmapWorkerTask getBitmapWorkerTask() { return bitmapWorkerTaskReference.get(); } } public Bitmap getBitmapFromMem(String url) { return mMemoryCache.get(url); } public void putBitmapToMem(String url, Bitmap bitmap) { mMemoryCache.put(url, bitmap); } @SuppressLint("NewApi") private void loadBitmap(ImageView imageView, String imageUrl, Bitmap placeHolder) { final Bitmap bitmap = getBitmapFromMemCache(imageUrl); if (bitmap != null) { imageView.setImageBitmap(bitmap); } else { if (cancelPotentialWork(imageUrl, imageView)) { final BitmapWorkerTask task = new BitmapWorkerTask(imageView); final AsyncDrawable asyncDrawable = new AsyncDrawable( mAppContext.getResources(), placeHolder, task); imageView.setImageDrawable(asyncDrawable); if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, imageUrl); } else { task.execute(imageUrl); } } } } public boolean cancelPotentialWork(String imageUrl, ImageView imageView) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { final String lastRequestUrl = bitmapWorkerTask.imageUrl; if (TextUtils.isEmpty(lastRequestUrl) || !lastRequestUrl.equals(imageUrl)) { bitmapWorkerTask.cancel(true); } else { // The same work is already in progress return false; } } // No task associated with the ImageView, or an existing task was // cancelled return true; } class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> { private WeakReference<ImageView> imageViewReference; private String imageUrl; public BitmapWorkerTask(ImageView imageView) { imageViewReference = new WeakReference<ImageView>(imageView); } @Override protected Bitmap doInBackground(String... params) { currencyNum.getAndIncrement(); System.err.println("xxxxxx" + currencyNum.get()); imageUrl = params[0]; Bitmap bitmap = getBitmapFromDiskCache(imageUrl); if (bitmap == null) { bitmap = downloadBitmap(imageUrl); } // Add final bitmap to caches if (bitmap != null) { addBitmapToCache(imageUrl, bitmap); } currencyNum.decrementAndGet(); return bitmap; } @Override protected void onPostExecute(Bitmap bitmap) { if (bitmap != null && imageViewReference != null) { ImageView imageView = imageViewReference.get(); if (imageView != null) { imageView.setImageBitmap(bitmap); } } } // TODO improve Bitmap downloadBitmap(String urlInString) { try { URL url = new URL(urlInString); HttpURLConnection urlConnection = (HttpURLConnection) url .openConnection(); urlConnection.connect(); final int statusCode = urlConnection.getResponseCode(); if (statusCode != 200) { Log.w("ImageDownloader", "Error " + statusCode + " while retrieving bitmap from " + url); return null; } Bitmap bitmap = null; InputStream inputStream = null; try { inputStream = urlConnection.getInputStream(); bitmap = BitmapFactory.decodeStream(inputStream); return bitmap; } finally { if (inputStream != null) { inputStream.close(); } } } catch (Exception e) { // Could provide a more explicit error message for IOException // or // IllegalStateException Log.w("ImageDownloader", "Error while retrieving bitmap from " + urlInString + " " + e.toString()); } finally { } return null; } public void addBitmapToCache(String imageUrl, Bitmap bitmap) { // Add to memory cache as before if (getBitmapFromMemCache(imageUrl) == null) { mMemoryCache.put(imageUrl, bitmap); } // Also add to disk cache synchronized (mDiskCacheLock) { try { if (mDiskLruCache != null && mDiskLruCache.get(MD5Utils .hashKeyForDisk(imageUrl)) == null) { DiskLruCache.Editor editor = mDiskLruCache .edit(MD5Utils.hashKeyForDisk(imageUrl)); if (editor != null) { OutputStream outputStream = editor .newOutputStream(0); if (bitmap.compress(CompressFormat.PNG, 100, outputStream)) { editor.commit(); } else { editor.abort(); } } } } catch (IOException e) { e.printStackTrace(); } } } public Bitmap getBitmapFromDiskCache(String imageUrl) { synchronized (mDiskCacheLock) { // Wait while disk cache is started from background thread while (mDiskCacheStarting) { try { mDiskCacheLock.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } if (mDiskLruCache != null) { DiskLruCache.Snapshot snapShot = null; try { snapShot = mDiskLruCache.get(MD5Utils .hashKeyForDisk(imageUrl)); } catch (IOException e) { e.printStackTrace(); } if (snapShot != null) { InputStream is = snapShot.getInputStream(0); Bitmap bitmap = BitmapFactory.decodeStream(is); return bitmap; } } } return null; } } private BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) { if (imageView != null) { final Drawable drawable = imageView.getDrawable(); if (drawable != null && drawable instanceof AsyncDrawable) { final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable; return asyncDrawable.getBitmapWorkerTask(); } } return null; } }
测试的图片内容类(这是某个csdn大牛的贡献,找不到名字了,在此谢过了)
package libcore.io; public class Images { public final static String[] imageThumbUrls = new String[] { "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383291_6518.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383291_8239.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383290_9329.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383290_1042.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383275_3977.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383265_8550.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383264_3954.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383264_4787.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383264_8243.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383248_3693.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383243_5120.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383242_3127.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383242_9576.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383242_1721.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383219_5806.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383214_7794.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383213_4418.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383213_3557.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383210_8779.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383172_4577.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383166_3407.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383166_2224.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383166_7301.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383165_7197.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383150_8410.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383131_3736.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383130_5094.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383130_7393.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383129_8813.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383100_3554.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383093_7894.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383092_2432.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383092_3071.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383091_3119.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383059_6589.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383059_8814.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383059_2237.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383058_4330.jpg", "http://img.my.csdn.net/uploads/201407/26/1406383038_3602.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382942_3079.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382942_8125.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382942_4881.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382941_4559.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382941_3845.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382924_8955.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382923_2141.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382923_8437.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382922_6166.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382922_4843.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382905_5804.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382904_3362.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382904_2312.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382904_4960.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382900_2418.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382881_4490.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382881_5935.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382880_3865.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382880_4662.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382879_2553.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382862_5375.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382862_1748.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382861_7618.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382861_8606.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382861_8949.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382841_9821.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382840_6603.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382840_2405.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382840_6354.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382839_5779.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382810_7578.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382810_2436.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382809_3883.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382809_6269.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382808_4179.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382790_8326.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382789_7174.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382789_5170.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382789_4118.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382788_9532.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382767_3184.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382767_4772.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382766_4924.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382766_5762.jpg", "http://img.my.csdn.net/uploads/201407/26/1406382765_7341.jpg" }; }
图片展示的adapter
package com.gch.loadimage; import libcore.io.ImageLoadGCH; import libcore.io.Images; import android.app.Activity; import android.content.Context; import android.view.View; import android.view.ViewGroup; import android.view.ViewGroup.LayoutParams; import android.widget.AbsListView; import android.widget.BaseAdapter; import android.widget.ImageView; import android.widget.LinearLayout; public class ImageAdapter extends BaseAdapter { Context mContext; int mScreenWidth = 0; public ImageAdapter(Context context) { mContext = context; mScreenWidth = FileUtil.getScreenWidth((Activity) context); } @Override public int getCount() { return Images.imageThumbUrls.length; } @Override public Object getItem(int position) { return Images.imageThumbUrls[position]; } @Override public long getItemId(int position) { return 0; } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder viewHolder = null; if (convertView == null) { viewHolder = new ViewHolder(); LinearLayout outerLayout = new LinearLayout(mContext); ImageView imageView = new ImageView(mContext); outerLayout.addView(imageView); AbsListView.LayoutParams outerParams = new AbsListView.LayoutParams( new LayoutParams(mScreenWidth / 3, mScreenWidth / 3)); outerLayout.setLayoutParams(outerParams); convertView = outerLayout; viewHolder.iconView = imageView; convertView.setTag(viewHolder); } else { viewHolder = (ViewHolder) convertView.getTag(); } ImageLoadGCH.getInstance(mContext.getApplicationContext()).loadImage( viewHolder.iconView, Images.imageThumbUrls[position], R.drawable.ic_launcher); viewHolder.iconView.setEnabled(false); return convertView; } class ViewHolder { ImageView iconView; } }
这是测试的MainActivity
package com.gch.loadimage; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.widget.GridView; public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // setContentView(R.layout.activity_main); GridView gridView = new GridView(this); setContentView(gridView); gridView.setNumColumns(3); gridView.setAdapter(new ImageAdapter(this)); } }
不要忘记添加权限哦
<uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
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