安卓开发笔记——关于照片墙的实现(完美缓存策略LruCache+DiskLruCache)

这几天一直研究在安卓开发中图片应该如何处理,在网上翻了好多资料,这里做点小总结,如果朋友们有更好的解决方案,可以留言一起交流下。

 

内存缓存技术

在我们开发程序中要在界面上加载一张图片是件非常容易的事情,但如果是加载一堆图片呢?比如ListView,GridView这类的控件,随着屏幕滑动,图片加载也会越来越多,应用程序所可以使用的内存毕竟是有限的,如果一味的去加载图片,很容易导致OOM(Out Of Memory)内存溢出,导致程序崩溃。

这里我们一般的做法是将显示在屏幕之外的图片进行内存回收,此时的垃圾回收器会认为应用对这些图片不再持有引用,从而进行GC操作。但现实还需要考虑到问题是,如果用户又滑动屏幕回到之前我们已经回收掉的图片位置,这时候该怎么办?重新去加载一张图片肯定是不可取的,这样既浪费了时间,又浪费了用户的流量。

这里我们就会想到利用内存缓存来解决这个问题,利用内存缓存可以让应用快速的加载和处理图片,从而提高流畅性。

内存缓存技术对那些大量占用应用程序宝贵内存的图片提供了快速访问的方法,其中最核心的类是LruCache (此类在android-support-v4的包中提供) 。这个类非常适合用来缓存图片,它的主要算法原理是把最近使用的对象用强引用存储在 LinkedHashMap 中,并且把最近最少使用的对象在缓存值达到预设定值之前从内存中移除。

在过去,我们经常会使用一种非常流行的内存缓存技术的实现,即软引用或弱引用 (SoftReference or WeakReference)。但是现在已经不再推荐使用这种方式了,因为从 Android 2.3 (API Level 9)开始,垃圾回收器会更倾向于回收持有软引用或弱引用的对象,这让软引用和弱引用变得不再可靠。另外,Android 3.0 (API Level 11)中,图片的数据会存储在本地的内存当中,因而无法用一种可预见的方式将其释放,这就有潜在的风险造成应用程序的内存溢出并崩溃。

对于LruCache类不熟悉的朋友可以看看这篇文章《Android高效加载大图、多图解决方案,有效避免程序OOM》。

 

磁盘缓存技术

对于内存缓存LruCache只是管理了内存中图片的存储与释放,如果图片从内存中被移除的话,那么又需要从网络上重新加载一次图片,这显然非常耗时。对此,Google又提供了一套硬盘缓存的解决方案:DiskLruCache(非Google官方编写,但获得官方认证)。

关于磁盘缓存DisLruCache类不熟悉的朋友可以看看这篇文章的介绍《Android DiskLruCache完全解析,硬盘缓存的最佳方案》  

 

 

 

完美结合LruCache+DiskLruCache

首先先来看下实现效果:

  

 

这是一个很简单的布局,大布局是GridView,小布局ImageView嵌套在大布局里,贴上代码再做分析吧,其实注释也挺全的。

既然要完成磁盘存储,那么必不可少的就是DisLruCache类的,先引进项目里再说,再来就是图片资源集合了。

图片资源类:

 1 package com.example.photoswall;
 2 
 3 
 4 /**
 5  * 图片资源类
 6  * @author Balla_兔子
 7  *
 8  */
 9 public class Images {
10 
11     public final static String[] imageThumbUrls = new String[] {
12         "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
13         "http://img.my.csdn.net/uploads/201407/26/1406383291_6518.jpg",
14         "http://img.my.csdn.net/uploads/201407/26/1406383291_8239.jpg",
15         "http://img.my.csdn.net/uploads/201407/26/1406383290_9329.jpg",
16         "http://img.my.csdn.net/uploads/201407/26/1406383290_1042.jpg",
17         "http://img.my.csdn.net/uploads/201407/26/1406383275_3977.jpg",
18         "http://img.my.csdn.net/uploads/201407/26/1406383265_8550.jpg",
19         "http://img.my.csdn.net/uploads/201407/26/1406383264_3954.jpg",
20         "http://img.my.csdn.net/uploads/201407/26/1406383264_4787.jpg",
21         "http://img.my.csdn.net/uploads/201407/26/1406383264_8243.jpg",
22         "http://img.my.csdn.net/uploads/201407/26/1406383248_3693.jpg",
23         "http://img.my.csdn.net/uploads/201407/26/1406383243_5120.jpg",
24         "http://img.my.csdn.net/uploads/201407/26/1406383242_3127.jpg",
25         "http://img.my.csdn.net/uploads/201407/26/1406383242_9576.jpg",
26         "http://img.my.csdn.net/uploads/201407/26/1406383242_1721.jpg",
27         "http://img.my.csdn.net/uploads/201407/26/1406383219_5806.jpg",
28         "http://img.my.csdn.net/uploads/201407/26/1406383214_7794.jpg",
29         "http://img.my.csdn.net/uploads/201407/26/1406383213_4418.jpg",
30         "http://img.my.csdn.net/uploads/201407/26/1406383213_3557.jpg",
31         "http://img.my.csdn.net/uploads/201407/26/1406383210_8779.jpg",
32         "http://img.my.csdn.net/uploads/201407/26/1406383172_4577.jpg",
33         "http://img.my.csdn.net/uploads/201407/26/1406383166_3407.jpg",
34         "http://img.my.csdn.net/uploads/201407/26/1406383166_2224.jpg",
35         "http://img.my.csdn.net/uploads/201407/26/1406383166_7301.jpg",
36         "http://img.my.csdn.net/uploads/201407/26/1406383165_7197.jpg",
37         "http://img.my.csdn.net/uploads/201407/26/1406383150_8410.jpg",
38         "http://img.my.csdn.net/uploads/201407/26/1406383131_3736.jpg",
39         "http://img.my.csdn.net/uploads/201407/26/1406383130_5094.jpg",
40         "http://img.my.csdn.net/uploads/201407/26/1406383130_7393.jpg",
41         "http://img.my.csdn.net/uploads/201407/26/1406383129_8813.jpg",
42         "http://img.my.csdn.net/uploads/201407/26/1406383100_3554.jpg",
43         "http://img.my.csdn.net/uploads/201407/26/1406383093_7894.jpg",
44         "http://img.my.csdn.net/uploads/201407/26/1406383092_2432.jpg",
45         "http://img.my.csdn.net/uploads/201407/26/1406383092_3071.jpg",
46         "http://img.my.csdn.net/uploads/201407/26/1406383091_3119.jpg",
47         "http://img.my.csdn.net/uploads/201407/26/1406383059_6589.jpg",
48         "http://img.my.csdn.net/uploads/201407/26/1406383059_8814.jpg",
49         "http://img.my.csdn.net/uploads/201407/26/1406383059_2237.jpg",
50         "http://img.my.csdn.net/uploads/201407/26/1406383058_4330.jpg",
51         "http://img.my.csdn.net/uploads/201407/26/1406383038_3602.jpg",
52         "http://img.my.csdn.net/uploads/201407/26/1406382942_3079.jpg",
53         "http://img.my.csdn.net/uploads/201407/26/1406382942_8125.jpg",
54         "http://img.my.csdn.net/uploads/201407/26/1406382942_4881.jpg",
55         "http://img.my.csdn.net/uploads/201407/26/1406382941_4559.jpg",
56         "http://img.my.csdn.net/uploads/201407/26/1406382941_3845.jpg",
57         "http://img.my.csdn.net/uploads/201407/26/1406382924_8955.jpg",
58         "http://img.my.csdn.net/uploads/201407/26/1406382923_2141.jpg",
59         "http://img.my.csdn.net/uploads/201407/26/1406382923_8437.jpg",
60         "http://img.my.csdn.net/uploads/201407/26/1406382922_6166.jpg",
61         "http://img.my.csdn.net/uploads/201407/26/1406382922_4843.jpg",
62         "http://img.my.csdn.net/uploads/201407/26/1406382905_5804.jpg",
63         "http://img.my.csdn.net/uploads/201407/26/1406382904_3362.jpg",
64         "http://img.my.csdn.net/uploads/201407/26/1406382904_2312.jpg",
65         "http://img.my.csdn.net/uploads/201407/26/1406382904_4960.jpg",
66         "http://img.my.csdn.net/uploads/201407/26/1406382900_2418.jpg",
67         "http://img.my.csdn.net/uploads/201407/26/1406382881_4490.jpg",
68         "http://img.my.csdn.net/uploads/201407/26/1406382881_5935.jpg",
69         "http://img.my.csdn.net/uploads/201407/26/1406382880_3865.jpg",
70         "http://img.my.csdn.net/uploads/201407/26/1406382880_4662.jpg",
71         "http://img.my.csdn.net/uploads/201407/26/1406382879_2553.jpg",
72         "http://img.my.csdn.net/uploads/201407/26/1406382862_5375.jpg",
73         "http://img.my.csdn.net/uploads/201407/26/1406382862_1748.jpg",
74         "http://img.my.csdn.net/uploads/201407/26/1406382861_7618.jpg",
75         "http://img.my.csdn.net/uploads/201407/26/1406382861_8606.jpg",
76         "http://img.my.csdn.net/uploads/201407/26/1406382861_8949.jpg",
77         "http://img.my.csdn.net/uploads/201407/26/1406382841_9821.jpg",
78         "http://img.my.csdn.net/uploads/201407/26/1406382840_6603.jpg",
79         "http://img.my.csdn.net/uploads/201407/26/1406382840_2405.jpg",
80         "http://img.my.csdn.net/uploads/201407/26/1406382840_6354.jpg",
81         "http://img.my.csdn.net/uploads/201407/26/1406382839_5779.jpg",
82         "http://img.my.csdn.net/uploads/201407/26/1406382810_7578.jpg",
83         "http://img.my.csdn.net/uploads/201407/26/1406382810_2436.jpg",
84         "http://img.my.csdn.net/uploads/201407/26/1406382809_3883.jpg",
85         "http://img.my.csdn.net/uploads/201407/26/1406382809_6269.jpg",
86         "http://img.my.csdn.net/uploads/201407/26/1406382808_4179.jpg",
87         "http://img.my.csdn.net/uploads/201407/26/1406382790_8326.jpg",
88         "http://img.my.csdn.net/uploads/201407/26/1406382789_7174.jpg",
89         "http://img.my.csdn.net/uploads/201407/26/1406382789_5170.jpg",
90         "http://img.my.csdn.net/uploads/201407/26/1406382789_4118.jpg",
91         "http://img.my.csdn.net/uploads/201407/26/1406382788_9532.jpg",
92         "http://img.my.csdn.net/uploads/201407/26/1406382767_3184.jpg",
93         "http://img.my.csdn.net/uploads/201407/26/1406382767_4772.jpg",
94         "http://img.my.csdn.net/uploads/201407/26/1406382766_4924.jpg",
95         "http://img.my.csdn.net/uploads/201407/26/1406382766_5762.jpg",
96         "http://img.my.csdn.net/uploads/201407/26/1406382765_7341.jpg"
97     };
98 }
View Code

DiskLruCache(磁盘缓存类):

  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.example.photoswall;
 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 file
116      * looks like this:
117      *     libcore.io.DiskLruCache
118      *     1
119      *     100
120      *     2
121      *
122      *     CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054
123      *     DIRTY 335c4c6028171cfddfbaae1a9c313c52
124      *     CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342
125      *     REMOVE 335c4c6028171cfddfbaae1a9c313c52
126      *     DIRTY 1ab96a171faeeee38496d8b330771a7a
127      *     CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234
128      *     READ 335c4c6028171cfddfbaae1a9c313c52
129      *     READ 3400330d1dfc7f3f7f4b8d4d803dfcf6
130      *
131      * The first five lines of the journal form its header. They are the
132      * 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 a
136      * 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 REMOVE
140      *     action. DIRTY lines without a matching CLEAN or REMOVE indicate that
141      *     temporary files may need to be deleted.
142      *   o CLEAN lines track a cache entry that has been successfully published
143      *     and may be read. A publish line is followed by the lengths of each of
144      *     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 may
149      * occasionally be compacted by dropping redundant lines. A temporary file named
150      * "journal.tmp" will be used during compaction; that file should be deleted if
151      * 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> lruEntries
163             = 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 given
168      * a sequence number each time an edit is committed. A snapshot is stale if
169      * 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[]) Array
186                 .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", or
210      * "\n".
211      *
212      * @throws java.io.EOFException if the stream is exhausted before the next newline
213      *     character.
214      */
215     public static String readAsciiLine(InputStream in) throws IOException {
216         // TODO: support UTF-8 here instead
217 
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 Files
254     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; // closed
277                 }
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 exists
299      * there.
300      *
301      * @param directory a writable directory
302      * @param appVersion
303      * @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 store
305      * @throws java.io.IOException if reading or writing the cache directory fails
306      */
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 off
317         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 cache
333         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 the
401      * 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 the
424      * 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't
470      * exist is not currently readable. If a value is returned, it is moved to
471      * 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 published
487          * snapshot. If we opened streams lazily then the streams could come
488          * 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 another
511      * 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_NUMBER
522                 && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {
523             return null; // snapshot is stale
524         }
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 progress
530         }
531 
532         Editor editor = new Editor(entry);
533         entry.currentEditor = editor;
534 
535         // flush the journal before creating files to prevent file leaks
536         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 store
550      * 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 in
558      * this cache. This may be greater than the max size if a background
559      * 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 value
572         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 journal
617      * 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_THRESHOLD
622                 && redundantOpCount >= lruEntries.size();
623     }
624 
625     /**
626      * Drops the entry for {@code key} if it exists and can be removed. Entries
627      * 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 closed
687         }
688         for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {
689             if (entry.currentEditor != null) {
690                 entry.currentEditor.abort();
691             }
692         }
693         trimToSize();
694         journalWriter.close();
695         journalWriter = null;
696     }
697 
698     private void trimToSize() throws IOException {
699         while (size > maxSize) {
700 //            Map.Entry<String, Entry> toEvict = lruEntries.eldest();
701             final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();
702             remove(toEvict.getKey());
703         }
704     }
705 
706     /**
707      * Closes the cache and deletes all of its stored values. This will delete
708      * all files in the cache directory including files that weren't created by
709      * the cache.
710      */
711     public void delete() throws IOException {
712         close();
713         deleteContents(directory);
714     }
715 
716     private void validateKey(String key) {
717         if (key.contains(" ") || key.contains("\n") || key.contains("\r")) {
718             throw new IllegalArgumentException(
719                     "keys must not contain spaces or newlines: \"" + key + "\"");
720         }
721     }
722 
723     private static String inputStreamToString(InputStream in) throws IOException {
724         return readFully(new InputStreamReader(in, UTF_8));
725     }
726 
727     /**
728      * A snapshot of the values for an entry.
729      */
730     public final class Snapshot implements Closeable {
731         private final String key;
732         private final long sequenceNumber;
733         private final InputStream[] ins;
734 
735         private Snapshot(String key, long sequenceNumber, InputStream[] ins) {
736             this.key = key;
737             this.sequenceNumber = sequenceNumber;
738             this.ins = ins;
739         }
740 
741         /**
742          * Returns an editor for this snapshot's entry, or null if either the
743          * entry has changed since this snapshot was created or if another edit
744          * is in progress.
745          */
746         public Editor edit() throws IOException {
747             return DiskLruCache.this.edit(key, sequenceNumber);
748         }
749 
750         /**
751          * Returns the unbuffered stream with the value for {@code index}.
752          */
753         public InputStream getInputStream(int index) {
754             return ins[index];
755         }
756 
757         /**
758          * Returns the string value for {@code index}.
759          */
760         public String getString(int index) throws IOException {
761             return inputStreamToString(getInputStream(index));
762         }
763 
764         @Override public void close() {
765             for (InputStream in : ins) {
766                 closeQuietly(in);
767             }
768         }
769     }
770 
771     /**
772      * Edits the values for an entry.
773      */
774     public final class Editor {
775         private final Entry entry;
776         private boolean hasErrors;
777 
778         private Editor(Entry entry) {
779             this.entry = entry;
780         }
781 
782         /**
783          * Returns an unbuffered input stream to read the last committed value,
784          * or null if no value has been committed.
785          */
786         public InputStream newInputStream(int index) throws IOException {
787             synchronized (DiskLruCache.this) {
788                 if (entry.currentEditor != this) {
789                     throw new IllegalStateException();
790                 }
791                 if (!entry.readable) {
792                     return null;
793                 }
794                 return new FileInputStream(entry.getCleanFile(index));
795             }
796         }
797 
798         /**
799          * Returns the last committed value as a string, or null if no value
800          * has been committed.
801          */
802         public String getString(int index) throws IOException {
803             InputStream in = newInputStream(index);
804             return in != null ? inputStreamToString(in) : null;
805         }
806 
807         /**
808          * Returns a new unbuffered output stream to write the value at
809          * {@code index}. If the underlying output stream encounters errors
810          * when writing to the filesystem, this edit will be aborted when
811          * {@link #commit} is called. The returned output stream does not throw
812          * IOExceptions.
813          */
814         public OutputStream newOutputStream(int index) throws IOException {
815             synchronized (DiskLruCache.this) {
816                 if (entry.currentEditor != this) {
817                     throw new IllegalStateException();
818                 }
819                 return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));
820             }
821         }
822 
823         /**
824          * Sets the value at {@code index} to {@code value}.
825          */
826         public void set(int index, String value) throws IOException {
827             Writer writer = null;
828             try {
829                 writer = new OutputStreamWriter(newOutputStream(index), UTF_8);
830                 writer.write(value);
831             } finally {
832                 closeQuietly(writer);
833             }
834         }
835 
836         /**
837          * Commits this edit so it is visible to readers.  This releases the
838          * edit lock so another edit may be started on the same key.
839          */
840         public void commit() throws IOException {
841             if (hasErrors) {
842                 completeEdit(this, false);
843                 remove(entry.key); // the previous entry is stale
844             } else {
845                 completeEdit(this, true);
846             }
847         }
848 
849         /**
850          * Aborts this edit. This releases the edit lock so another edit may be
851          * started on the same key.
852          */
853         public void abort() throws IOException {
854             completeEdit(this, false);
855         }
856 
857         private class FaultHidingOutputStream extends FilterOutputStream {
858             private FaultHidingOutputStream(OutputStream out) {
859                 super(out);
860             }
861 
862             @Override public void write(int oneByte) {
863                 try {
864                     out.write(oneByte);
865                 } catch (IOException e) {
866                     hasErrors = true;
867                 }
868             }
869 
870             @Override public void write(byte[] buffer, int offset, int length) {
871                 try {
872                     out.write(buffer, offset, length);
873                 } catch (IOException e) {
874                     hasErrors = true;
875                 }
876             }
877 
878             @Override public void close() {
879                 try {
880                     out.close();
881                 } catch (IOException e) {
882                     hasErrors = true;
883                 }
884             }
885 
886             @Override public void flush() {
887                 try {
888                     out.flush();
889                 } catch (IOException e) {
890                     hasErrors = true;
891                 }
892             }
893         }
894     }
895 
896     private final class Entry {
897         private final String key;
898 
899         /** Lengths of this entry's files. */
900         private final long[] lengths;
901 
902         /** True if this entry has ever been published */
903         private boolean readable;
904 
905         /** The ongoing edit or null if this entry is not being edited. */
906         private Editor currentEditor;
907 
908         /** The sequence number of the most recently committed edit to this entry. */
909         private long sequenceNumber;
910 
911         private Entry(String key) {
912             this.key = key;
913             this.lengths = new long[valueCount];
914         }
915 
916         public String getLengths() throws IOException {
917             StringBuilder result = new StringBuilder();
918             for (long size : lengths) {
919                 result.append(' ').append(size);
920             }
921             return result.toString();
922         }
923 
924         /**
925          * Set lengths using decimal numbers like "10123".
926          */
927         private void setLengths(String[] strings) throws IOException {
928             if (strings.length != valueCount) {
929                 throw invalidLengths(strings);
930             }
931 
932             try {
933                 for (int i = 0; i < strings.length; i++) {
934                     lengths[i] = Long.parseLong(strings[i]);
935                 }
936             } catch (NumberFormatException e) {
937                 throw invalidLengths(strings);
938             }
939         }
940 
941         private IOException invalidLengths(String[] strings) throws IOException {
942             throw new IOException("unexpected journal line: " + Arrays.toString(strings));
943         }
944 
945         public File getCleanFile(int i) {
946             return new File(directory, key + "." + i);
947         }
948 
949         public File getDirtyFile(int i) {
950             return new File(directory, key + "." + i + ".tmp");
951         }
952     }
953 }
View Code

MD5Utils(MD5转换工具类):

 1 package com.example.photoswall;
 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0
21         for (int i = 0; i < 32 - md5code.length(); i++) {
22             md5code = "0" + md5code;
23         }
24         return md5code;
25     }
26 
27 }
View Code

上面三个类直接引入项目就行了,接下来说说核心实现代码了。

PhotoWallAdapter(GridView适配器类):

说下思路:由于我们的图片源是单纯的字符串(网址),这里给GridView适配的Adpter采用ArrayAdapter,当然如果你想用BaseAdatper也是可以的,思路不变。

1、继承ArrayAdatper,在构造函数传入必要参数后,需要进行2个操作:1、对内存缓存类的初始化  2、对磁盘缓存的初始化

2、然后在getView方法中来设置图片源,首先先设置成一张默认的图片,然后根据图片的URL去缓存中找是否有相关联的资源,如果没找到在磁盘缓存中找,如果还是没找到再去网络上下载,然后保存在磁盘缓存里,在以上的任一环节(磁盘,网络)里,只要我们找到了相对的图片资源,我们就把它添加到内存缓存中,以便下一次的引用。为了避免异步下载图片造成的图片错位现象,我们在每一个ImageView里设置了一个标识符Tag,Tag为图片的唯一标志:URL地址。

3、由于磁盘缓存属于I/O操作,网络属于下载操作都是属于耗时性的工作,这里我们开启了一个内部类Async异步类去完成,把所有的耗时操作都安排在doInBackground里执行(这里选择Async而不选择直接new Thread的原因是,Async运用了线程池的概念,会比单开子线程会更省资源,而且所有的任务会按照队列的顺序去执行)

 由于这里的图片都是比较小的,在实际开发中,大家可以对利用BitmapFactory的Options类对图片进行压缩再展示。

  1 package com.example.photoswall;
  2 
  3 import java.io.BufferedInputStream;
  4 import java.io.BufferedOutputStream;
  5 import java.io.File;
  6 import java.io.IOException;
  7 import java.io.OutputStream;
  8 import java.net.HttpURLConnection;
  9 import java.net.URL;
 10 import java.util.HashSet;
 11 import java.util.Set;
 12 
 13 import android.content.Context;
 14 import android.content.pm.PackageInfo;
 15 import android.content.pm.PackageManager.NameNotFoundException;
 16 import android.graphics.Bitmap;
 17 import android.graphics.BitmapFactory;
 18 import android.os.AsyncTask;
 19 import android.os.Environment;
 20 import android.support.v4.util.LruCache;
 21 import android.util.Log;
 22 import android.view.LayoutInflater;
 23 import android.view.View;
 24 import android.view.ViewGroup;
 25 import android.widget.ArrayAdapter;
 26 import android.widget.GridView;
 27 import android.widget.ImageView;
 28 
 29 import com.example.photoswall.DiskLruCache.Snapshot;
 30 
 31 public class PhotoWallAdapter extends ArrayAdapter<String> {
 32 
 33     // 声明LruCache缓存对象
 34     private LruCache<String, Bitmap> lruCache;
 35     // 声明DiskLruCache硬盘缓存对象
 36     private DiskLruCache diskLruCache;
 37     // 任务队列
 38     private Set<LoadImageAsync> tasks;
 39     // 声明GridView对象
 40     private GridView gridView;
 41 
 42     public PhotoWallAdapter(Context context, int textViewResourceId, String[] objects, GridView gridView) {
 43         super(context, textViewResourceId, objects);
 44         this.gridView = gridView;
 45         tasks = new HashSet<LoadImageAsync>();
 46         /**
 47          * 初始化内存缓存LruCache
 48          */
 49         // 获取应用程序最大可占内存值
 50         int maxMemory = (int) Runtime.getRuntime().maxMemory();
 51         // 设置最大内存的八分之一作为缓存大小
 52         int lruMemory = maxMemory / 8;
 53         lruCache = new LruCache<String, Bitmap>(lruMemory) {
 54             @Override
 55             protected int sizeOf(String key, Bitmap bitmap) {
 56                 // 返回Bitmap对象所占大小,单位:kb
 57                 return bitmap.getByteCount();
 58             }
 59 
 60         };
 61         /**
 62          * 初始化硬盘缓存DiskLruCahce
 63          */
 64         // 获取硬盘缓存路径,参数二为所在缓存路径的文件夹名称
 65         File directory = getDiskCacheDir(getContext(), "bitmap");
 66         if (!directory.exists()) {
 67             // 若文件夹不存在,建立文件夹
 68             directory.mkdirs();
 69         }
 70         int appVersion = getAppVersion(getContext());
 71         try {
 72             // 参数1:缓存文件路径,参数2:系统版本号,参数3:一个缓存路径对于几个文件,参数4:缓存空间大小:字节
 73             diskLruCache = DiskLruCache.open(directory, appVersion, 1, 1024 * 1024 * 10);
 74         } catch (IOException e) {
 75             e.printStackTrace();
 76         }
 77 
 78     }
 79 
 80     /**
 81      * @param context
 82      * @param uniqueName
 83      * @return 
 84      *         当SD卡存在或者SD卡不可被移除的时候,就调用getExternalCacheDir()方法来获取缓存路径,否则就调用getCacheDir
 85      *         ()方法来获取缓存路径。 前者获取到的就是 /sdcard/Android/data/<application
 86      *         package>/cache 这个路径 而后者获取到的是 datadata/application package>/cache
 87      *         这个路径。
 88      */
 89     public File getDiskCacheDir(Context context, String uniqueName) {
 90         String cachePath;
 91         if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !Environment.isExternalStorageRemovable()) {
 92             cachePath = context.getExternalCacheDir().getPath();
 93         } else {
 94             cachePath = context.getCacheDir().getPath();
 95         }
 96         return new File(cachePath + File.separator + uniqueName);
 97     }
 98 
 99     /**
100      * @param context
101      * @return 获取系统版本号
102      */
103     public int getAppVersion(Context context) {
104         try {
105             PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
106             return info.versionCode;
107         } catch (NameNotFoundException e) {
108             e.printStackTrace();
109         }
110         return 1;
111     }
112 
113     @Override
114     public View getView(int position, View convertView, ViewGroup parent) {
115         // 获取图片资源URL地址
116         String path = getItem(position);
117         View view = null;
118         if (convertView == null) {
119             view = LayoutInflater.from(getContext()).inflate(R.layout.gridview_item, null);
120         } else {
121             view = convertView;
122         }
123         // 获取控件实例
124         ImageView imageView = (ImageView) view.findViewById(R.id.iv_photo);
125         // 设置一个唯一标识符,避免异步加载图片时错位
126         imageView.setTag(path);
127         // 设置默认图片
128         imageView.setImageResource(R.drawable.ic_launcher);
129         // 根据图片URL到缓存中去找图片资源并设置
130         setImageFromLruCache(path, imageView);
131         return view;
132     }
133 
134     /**
135      * 根据图片URL地址获取缓存中图片,若不存在去磁盘缓存中查找=》网络下载
136      * 
137      * @param path
138      * @param imageView
139      */
140     private void setImageFromLruCache(String path, ImageView imageView) {
141         Bitmap bitmap = lruCache.get(path);
142         if (bitmap != null) {
143             // 缓存存在,取出设置图片
144             Log.i("PhotoWallAdapter", "在内存缓存中找到");
145             imageView.setImageBitmap(bitmap);
146         } else {
147             // 缓存不存在,先找硬盘缓存,还不存在,就去网络下载(开启异步任务)
148             LoadImageAsync loadImageAsync = new LoadImageAsync();
149             loadImageAsync.execute(path);
150             // 添加任务到任务队列
151             tasks.add(loadImageAsync);
152         }
153     }
154 
155     /**
156      * 取消队列中准备下载和正在下载的任务
157      */
158     public void cancelTask() {
159         for (LoadImageAsync task : tasks) {
160             task.cancel(false);
161         }
162     }
163 
164     /**
165      * 同步内存操作到journal文件
166      */
167     public void flushCache() {
168         if (diskLruCache != null) {
169             try {
170                 diskLruCache.flush();
171             } catch (IOException e) {
172                 e.printStackTrace();
173             }
174         }
175 
176     }
177 
178     class LoadImageAsync extends AsyncTask<String, Void, Bitmap> {
179         // 图片资源URL
180         String path = null;
181 
182         @Override
183         protected Bitmap doInBackground(String... params) {
184             // 图片下载地址
185             this.path = params[0];
186             Snapshot snapshot = null;
187             OutputStream outputStream = null;
188             Bitmap bitmap = null;
189             String pathMd5 = MD5Utils.md5(path);
190             // 根据图片url(md5)查找图片资源是否存在于硬盘缓存
191             try {
192                 snapshot = diskLruCache.get(pathMd5);
193                 if (snapshot == null) {
194                     // 在磁盘缓存中没有找到图片资源
195                     // 获取一个DiskLruCache写入对象
196                     DiskLruCache.Editor editor = diskLruCache.edit(pathMd5);
197                     if (editor != null) {
198                         outputStream = editor.newOutputStream(0);
199                         // 开启异步网络任务获取图片,并存入磁盘缓存
200                         if (downloadUrlToStream(path, outputStream)) {
201                             // 下载成功
202                             Log.i("PhotoWallAdapter", "下载文件成功");
203                             editor.commit();
204                         } else {
205                             editor.abort();
206                         }
207                     }
208                 }
209                 // 图片写入磁盘缓存后,再一次的查找磁盘缓存
210                 snapshot = diskLruCache.get(pathMd5);
211                 if (snapshot != null) {
212                     // 若查找到,获取图片,并把图片资源写入内存缓存
213                     bitmap = BitmapFactory.decodeStream(snapshot.getInputStream(0));
214                     Log.i("PhotoWallAdapter", "在磁盘缓存中找到");
215                 }
216                 if (bitmap != null) {
217                     // 将Bitmap对象添加到内存缓存当中
218                     lruCache.put(path, bitmap);
219                 }
220                 return bitmap;
221             } catch (IOException e) {
222                 e.printStackTrace();
223             } finally {
224                 if (outputStream != null) {
225                     try {
226                         outputStream.close();
227                     } catch (IOException e) {
228                         e.printStackTrace();
229                     }
230                 }
231             }
232             return null;
233         }
234 
235         @Override
236         protected void onPostExecute(Bitmap bitmap) {
237             super.onPostExecute(bitmap);
238             // 根据Tag获取控件对象并设置图片
239             ImageView imageView = (ImageView) gridView.findViewWithTag(path);
240             if (imageView != null && bitmap != null) {
241                 // 加载图片
242                 imageView.setImageBitmap(bitmap);
243             }
244             tasks.remove(this);
245 
246         }
247 
248         /**
249          * 根据图片URL地址下载图片,成功返回true,失败false
250          * 
251          * @param urlString
252          * @param outputStream
253          * @return
254          */
255         private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
256             HttpURLConnection urlConnection = null;
257             BufferedOutputStream out = null;
258             BufferedInputStream in = null;
259             try {
260                 final URL url = new URL(urlString);
261                 urlConnection = (HttpURLConnection) url.openConnection();
262                 in = new BufferedInputStream(urlConnection.getInputStream(), 8 * 1024);
263                 out = new BufferedOutputStream(outputStream, 8 * 1024);
264                 int b;
265                 while ((b = in.read()) != -1) {
266                     out.write(b);
267                 }
268                 return true;
269             } catch (final IOException e) {
270                 e.printStackTrace();
271             } finally {
272                 if (urlConnection != null) {
273                     urlConnection.disconnect();
274                 }
275                 try {
276                     if (out != null) {
277                         out.close();
278                     }
279                     if (in != null) {
280                         in.close();
281                     }
282                 } catch (final IOException e) {
283                     e.printStackTrace();
284                 }
285             }
286             return false;
287         }
288 
289     }
290 
291 }

 MainActivity类:

相比之下这个类就简单许多了,这里需要注意的两点:

1、在onPause方法里进行flush操作(更新磁盘缓存操作日志,磁盘缓存之所以能够被读取取决于日志文件)

2、在Activity销毁之前取消所有正在下载和准备下载的任务。

 1 package com.example.photoswall;
 2 
 3 import android.app.Activity;
 4 import android.os.Bundle;
 5 import android.widget.GridView;
 6 
 7 public class MainActivity extends Activity {
 8 
 9     private GridView gv_photo;
10     private PhotoWallAdapter adapter;
11 
12     @Override
13     protected void onCreate(Bundle savedInstanceState) {
14         super.onCreate(savedInstanceState);
15         setContentView(R.layout.activity_main);
16         gv_photo = (GridView) findViewById(R.id.gv_photo);
17         adapter = new PhotoWallAdapter(MainActivity.this, 0, Images.imageThumbUrls, gv_photo);
18         gv_photo.setAdapter(adapter);
19 
20     }
21 
22     @Override
23     protected void onPause() {
24         super.onPause();
25         adapter.flushCache();
26     }
27 
28     @Override
29     protected void onDestroy() {
30         super.onDestroy();
31         adapter.cancelTask();
32     }
33 
34 }

 

剩下的一些细节,代码注释的很详细,还有不清楚的可以看看上文提到附带的2篇文章或者评论给我留言。

 

作者:Balla_兔子
出处:http://www.cnblogs.com/lichenwei/
本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文链接。
正在看本人博客的这位童鞋,我看你气度不凡,谈吐间隐隐有王者之气,日后必有一番作为!旁边有“推荐”二字,你就顺手把它点了吧,相得准,我分文不收;相不准,你也好回来找我!

posted @ 2015-04-21 01:53  李晨玮  阅读(...)  评论(... 编辑 收藏