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android读取大图片并缓存

https://blog.csdn.net/liliang497/article/details/7221110


最近开发电视版的云存储应用，要求”我的相册“模块有全屏预览图片的功能，全屏分辨率是1920*1080超清。

UI组件方面采用Gallery+ImageSwitcher组合，这里略过，详情参见google Android API。

相册图片预取缓存策略是内存缓存（硬引用LruCache、软引用SoftReference<Bitmap>）、外部文件缓存（context.getCachedDir()），缓存中取不到的情况下再向服务端请求下载图片。同时缓存三张图片（当前预览的这张，前一张以及后一张）。

1.内存缓存

  1. //需要导入外部jar文件 android-support-v4.jar
  2. import android.support.v4.util.LruCache;
  3. //开辟8M硬缓存空间
  4. private final int hardCachedSize = 8*1024*1024;
  5. //hard cache
  6. private final LruCache<String, Bitmap> sHardBitmapCache = new LruCache<String, Bitmap>(hardCachedSize){
  7. @Override
  8. public int sizeOf(String key, Bitmap value){
  9. return value.getRowBytes() * value.getHeight();
  10. }
  11. @Override
  12. protected void entryRemoved(boolean evicted, String key, Bitmap oldValue, Bitmap newValue){
  13. Log.v("tag", "hard cache is full , push to soft cache");
  14. //硬引用缓存区满，将一个最不经常使用的oldvalue推入到软引用缓存区
  15. sSoftBitmapCahe.put(key, new SoftReference<Bitmap>(oldValue));
  16. }
  17. }
  18. //软引用
  19. private static final int SOFT_CACHE_CAPACITY = 40;
  20. private final static LinkedHashMap<String, SoftReference<Bitmap>> sSoftBitmapCache =
  21. new LinkedHashMao<String, SoftReference<Bitmap>>(SOFT_CACHE_CAPACITY, 0.75f, true){
  22. @Override
  23. public SoftReference<Bitmap> put(String key, SoftReference<Bitmap> value){
  24. return super.input(key, value);
  25. }
  26. @Override
  27. protected boolean removeEldestEntry(LinkedHashMap.Entry<Stirng, SoftReference<Bitmap>> eldest){
  28. if(size() > SOFT_CACHE_CAPACITY){
  29. Log.v("tag", "Soft Reference limit , purge one");
  30. return true;
  31. }
  32. return false;
  33. }
  34. }
  35. //缓存bitmap
  36. public boolean putBitmap(String key, Bitmap bitmap){
  37. if(bitmap != null){
  38. synchronized(sHardBitmapCache){
  39. sHardBitmapCache.put(key, bitmap);
  40. }
  41. return true;
  42. }
  43. return false;
  44. }
  45. //从缓存中获取bitmap
  46. public Bitmap getBitmap(String key){
  47. synchronized(sHardBitmapCache){
  48. final Bitmap bitmap = sHardBitmapCache.get(key);
  49. if(bitmap != null)
  50. return bitmap;
  51. }
  52. //硬引用缓存区间中读取失败，从软引用缓存区间读取
  53. synchronized(sSoftBitmapCache){
  54. SoftReference<Bitmap> bitmapReference = sSoftBtimapCache.get(key);
  55. if(bitmapReference != null){
  56. final Bitmap bitmap2 = bitmapReference.get();
  57. if(bitmap2 != null)
  58. return bitmap2;
  59. else{
  60. Log.v("tag", "soft reference 已经被回收");
  61. sSoftBitmapCache.remove(key);
  62. }
  63. }
  64. }
  65. return null;
  66. }
//需要导入外部jar文件 android-support-v4.jar import android.support.v4.util.LruCache; //开辟8M硬缓存空间 private final int hardCachedSize = 8*1024*1024; //hard cache private final LruCache<String, Bitmap> sHardBitmapCache = new LruCache<String, Bitmap>(hardCachedSize){ @Override public int sizeOf(String key, Bitmap value){ return value.getRowBytes() * value.getHeight(); } @Override protected void entryRemoved(boolean evicted, String key, Bitmap oldValue, Bitmap newValue){ Log.v("tag", "hard cache is full , push to soft cache"); //硬引用缓存区满，将一个最不经常使用的oldvalue推入到软引用缓存区 sSoftBitmapCahe.put(key, new SoftReference<Bitmap>(oldValue)); } } //软引用 private static final int SOFT_CACHE_CAPACITY = 40; private final static LinkedHashMap<String, SoftReference<Bitmap>> sSoftBitmapCache = new LinkedHashMao<String, SoftReference<Bitmap>>(SOFT_CACHE_CAPACITY, 0.75f, true){ @Override public SoftReference<Bitmap> put(String key, SoftReference<Bitmap> value){ return super.input(key, value); } @Override protected boolean removeEldestEntry(LinkedHashMap.Entry<Stirng, SoftReference<Bitmap>> eldest){ if(size() > SOFT_CACHE_CAPACITY){ Log.v("tag", "Soft Reference limit , purge one"); return true; } return false; } } //缓存bitmap public boolean putBitmap(String key, Bitmap bitmap){ if(bitmap != null){ synchronized(sHardBitmapCache){ sHardBitmapCache.put(key, bitmap); } return true; } return false; } //从缓存中获取bitmap public Bitmap getBitmap(String key){ synchronized(sHardBitmapCache){ final Bitmap bitmap = sHardBitmapCache.get(key); if(bitmap != null) return bitmap; } //硬引用缓存区间中读取失败，从软引用缓存区间读取 synchronized(sSoftBitmapCache){ SoftReference<Bitmap> bitmapReference = sSoftBtimapCache.get(key); if(bitmapReference != null){ final Bitmap bitmap2 = bitmapReference.get(); if(bitmap2 != null) return bitmap2; else{ Log.v("tag", "soft reference 已经被回收"); sSoftBitmapCache.remove(key); } } } return null; }

2.外部文件缓存

  1. private File mCacheDir = context.getCacheDir();
  2. private static final int MAX_CACHE_SIZE = 20 * 1024 * 1024; //20M
  3. private final LruCache<String, Long> sFileCache = new LruCache<String, Long>(MAX_CACHE_SIZE){
  4. @Override
  5. public int sizeOf(String key, Long value){
  6. return value.intValue();
  7. }
  8. @Override
  9. protected void entryRemoved(boolean evicted, String key, Long oldValue, Long newValue){
  10. File file = getFile(key);
  11. if(file != null)
  12. file.delete();
  13. }
  14. }
  15. private File getFile(String fileName) throws FileNotFoundException {
  16. File file = new File(mCacheDir, fileName);
  17. if(!file.exists() || !file.isFile())
  18. throw new FileNotFoundException("文件不存在或有同名文件夹");
  19. return file;
  20. }
  21. //缓存bitmap到外部存储
  22. public boolean putBitmap(String key, Bitmap bitmap){
  23. File file = getFile(key);
  24. if(file != null){
  25. Log.v("tag", "文件已经存在");
  26. return true;
  27. }
  28. FileOutputStream fos = getOutputStream(key);
  29. boolean saved = bitmap.compress(CompressFormat.JPEG, 100, fos);
  30. fos.flush();
  31. fos.close();
  32. if(saved){
  33. synchronized(sFileCache){
  34. sFileCache.put(key, getFile(key).length());
  35. }
  36. return true;
  37. }
  38. return false;
  39. }
  40. //根据key获取OutputStream
  41. private FileOutputStream getOutputStream(String key){
  42. if(mCacheDir == null)
  43. return null;
  44. FileOutputStream fos = new FileOutputStream(mCacheDir.getAbsolutePath() + File.separator + key);
  45. return fos;
  46. }
  47. //获取bitmap
  48. private static BitmapFactory.Options sBitmapOptions;
  49. static {
  50. sBitmapOptions = new BitmapFactory.Options();
  51. sBitmapOptions.inPurgeable=true; //bitmap can be purged to disk
  52. }
  53. public Bitmap getBitmap(String key){
  54. File bitmapFile = getFile(key);
  55. if(bitmapFile != null){
  56. Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(bitmapFile), null, sBitmapOptions);
  57. if(bitmap != null){
  58. //重新将其缓存至硬引用中
  59. ...
  60. }
  61. }
  62. }
private File mCacheDir = context.getCacheDir(); private static final int MAX_CACHE_SIZE = 20 * 1024 * 1024; //20M private final LruCache<String, Long> sFileCache = new LruCache<String, Long>(MAX_CACHE_SIZE){ @Override public int sizeOf(String key, Long value){ return value.intValue(); } @Override protected void entryRemoved(boolean evicted, String key, Long oldValue, Long newValue){ File file = getFile(key); if(file != null) file.delete(); } } private File getFile(String fileName) throws FileNotFoundException { File file = new File(mCacheDir, fileName); if(!file.exists() || !file.isFile()) throw new FileNotFoundException("文件不存在或有同名文件夹"); return file; } //缓存bitmap到外部存储 public boolean putBitmap(String key, Bitmap bitmap){ File file = getFile(key); if(file != null){ Log.v("tag", "文件已经存在"); return true; } FileOutputStream fos = getOutputStream(key); boolean saved = bitmap.compress(CompressFormat.JPEG, 100, fos); fos.flush(); fos.close(); if(saved){ synchronized(sFileCache){ sFileCache.put(key, getFile(key).length()); } return true; } return false; } //根据key获取OutputStream private FileOutputStream getOutputStream(String key){ if(mCacheDir == null) return null; FileOutputStream fos = new FileOutputStream(mCacheDir.getAbsolutePath() + File.separator + key); return fos; } //获取bitmap private static BitmapFactory.Options sBitmapOptions; static { sBitmapOptions = new BitmapFactory.Options(); sBitmapOptions.inPurgeable=true; //bitmap can be purged to disk } public Bitmap getBitmap(String key){ File bitmapFile = getFile(key); if(bitmapFile != null){ Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(bitmapFile), null, sBitmapOptions); if(bitmap != null){ //重新将其缓存至硬引用中 ... } } }


3.从服务端下载图片

下载成功后调用1内存缓存的putBitmap()函数,缓存图片。

在外部文件缓存中也写入一份，调用2的putBitmap()函数.

4.预览图片的流程

1) 如果预览的图片在内存缓存区中，直接调用1的getBitmap()函数，获取bitmap数据(先在硬引用缓存区查找匹配，若硬引用区匹配失败，再去软引用区匹配)

2) 如果从内存缓存区读取失败，再从外部文件缓存中读取，调用2的getBitmap()函数

3) 如果从外部文件缓存中读取失败，则从服务端下载该图片，过程3.

5.生成key值

  1. private static String generateKey(String fileId, int width, int height) {
  2. String ret = fileId + "_" + Integer.toString(width) + "x" + Integer.toString(height);
  3. return ret;
  4. }
  5. String key = generateKey(...)即可生成唯一的key值  

最后更新：2017-04-02 17:28:41

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