Bitmap之内存缓存和磁盘缓存详解

• Bitmap之位图采样和内存计算详解

内存缓存

LruCache 的使用

1. 初始化 LruCache

//第一种方式：
ActivityManager manager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
//获取当前硬件条件下应用所占的大致内存大小，单位为M
int memorySize = manager.getMemoryClass();//M
int cacheSize = memorySize/ 8;
//第二种方式（比较常用）
int memorySize = (int) Runtime.getRuntime().maxMemory();//bytes
int cacheSize = memorySize / 8;

//初始化 LruCache 且设置了缓存大小
LruCache<String,Bitmap> lruCache = new LruCache<String,Bitmap>(cacheSize){
    @Override
    protected int sizeOf(String key,Bitmap value) {
        //计算每一个缓存Bitmap的所占内存的大小,内存单位应该和 cacheSize 的单位保持一致
        return value.getByteCount();
    }
};

2. 添加 Bitmap 对象到 LruCache 缓存中

//参数put(String key，Bitmap bitmap)
lruCache.put(key,bitmap)

3. 获取缓存中的图片并显示

//参数get(String key)
Bitmap bitmap = lruCache.get(key);
imageView.setImageBitmap(bitmap);

加载网络图片

//ImageLoader
public class ImageLoader {
    private LruCache<String,Bitmap> lruCache;
    public ImageLoader() {
        int memorySize = (int) Runtime.getRuntime().maxMemory() / 1024;

        int cacheSize = memorySize / 8;
        lruCache = new LruCache<String,Bitmap>(cacheSize){
            @Override
            protected int sizeOf(String key,Bitmap value) {
                //计算每一个缓存Bitmap的所占内存的大小
                return value.getByteCount()/1024;
            }
        };
    }

    /**
     * 添加Bitmapd到LruCache中
     * @param key
     * @param bitmap
     */
    public void addBitmapToLruCache(String key,Bitmap bitmap){
        if (getBitmapFromLruCache(key)==null){
            lruCache.put(key,bitmap);
        }
    }

    /**
     * 获取缓存的Bitmap
     * @param key
     */
    public Bitmap getBitmapFromLruCache(String key){
        if (key!=null){
            return lruCache.get(key);
        }
        return null;
    }

    /**
     * 移出缓存
     * @param key
     */
    public void removeBitmapFromLruCache(String key){
        if (key!=null){
            lruCache.remove(key);
        }
    }
}

//加载图片的线程
public class LoadImageThread extends Thread {
    private Activity mActivity;
    private String mImageUrl;
    private ImageLoader mImageLoader;
    private ImageView mImageView;

    public LoadImageThread(Activity activity,ImageLoader imageLoader,ImageView imageView,String imageUrl) {
        this.mActivity = activity;
        this.mImageLoader = imageLoader;
        this.mImageView = imageView;
        this.mImageUrl = imageUrl;
    }

    @Override
    public void run() {
        HttpURLConnection connection = null;
        InputStream is = null;
        try {
            URL url = new URL(mImageUrl);
            connection = (HttpURLConnection) url.openConnection();
            is = connection.getInputStream();
            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK){
                final Bitmap bitmap = BitmapFactory.decodeStream(is);
                mImageLoader.addBitmapToLruCache("bitmap",bitmap);
                mActivity.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        mImageView.setImageBitmap(bitmap);
                    }
                });
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (connection!=null){
                connection.disconnect();
            }
            if (is!=null){
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

//获取图片
private void loadImage(){
    Bitmap bitmap = imageLoader.getBitmapFromLruCache("bitmap");
   if (bitmap==null){
       Log.i(TAG,"从网络获取图片");
       new LoadImageThread(this,imageLoader,imageView,url).start();
   }else{
       Log.i(TAG,"从缓存中获取图片");
       imageView.setImageBitmap(bitmap);
   }
}

// 移出缓存
private void removeBitmapFromL(String key){
    imageLoader.removeBitmapFromLruCache(key);
}

@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.btnLoadLruCache:
            loadImage();
            break;
        case R.id.btnRemoveBitmapL:
            removeBitmapFromL("bitmap");
            break;
    }
}

磁盘缓存

DiskLruCache 的创建

/**
 * 返回相应目录中的缓存，如果不存在则创建
 * @param directory 缓存目录
 * @param appVersion 表示应用的版本号，一般设为1
 * @param valueCount 每个Key所对应的Value的数量，一般设为1
 * @param maxSize 缓存大小
 * @throws IOException if reading or writing the cache directory fails
 */
public static DiskLruCache open(File directory,int appVersion,int valueCount,long maxSize)
        throws IOException {
    ...
    // 创建DiskLruCache
    DiskLruCache cache = new DiskLruCache(directory,appVersion,valueCount,maxSize);
    if (cache.journalFile.exists()) {
        ...
        return cache;
    }
    //如果缓存目录不存在，创建缓存目录以及DiskLruCache
    directory.mkdirs();
    cache = new DiskLruCache(directory,maxSize);
    ...
    return cache;
}

DiskLruCache 缓存的添加

//计算url的MD5值作为key
private String hashKeyForDisk(String url) {
    String cacheKey;
    try {
        final MessageDigest mDigest = MessageDigest.getInstance("MD5");
        mDigest.update(url.getBytes());
        cacheKey = bytesToHexString(mDigest.digest());
    } catch (NoSuchAlgorithmException e) {
        cacheKey = String.valueOf(url.hashCode());
    }
    return cacheKey;
}

private 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();
}

1. 创建 OutputStream 写入要缓存的数据，通过 DiskLruCache 的 edit(String key) 方法获得 Editor 对象，然后通过 OutputStream 转换为 Birmap，将该 Bitmap 写入由 Editor 对象创建的 OutputStream 中，最后调用 Editor 对象的 commit 方法提交；
2. 先获得 Editor 对象，根据 Editor 对象创建出 OutputStream 直接写入要缓存的数据，最后调用 Editor 对象的 commit 方法提交；

//添加网络图片到内存缓存和磁盘缓存
public void putCache(final String url,final CallBack callBack){
    Log.i(TAG,"putCache...");
    new AsyncTask<String,Void,Bitmap>(){
        @Override
        protected Bitmap doInBackground(String... params) {
            String key = hashKeyForDisk(params[0]);
            DiskLruCache.Editor editor = null;
            Bitmap bitmap = null;
            try {
                URL url = new URL(params[0]);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setReadTimeout(1000 * 30);
                conn.setConnectTimeout(1000 * 30);
                ByteArrayOutputStream baos = null;
                if(conn.getResponseCode()==HttpURLConnection.HTTP_OK){
                    BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());
                    baos = new ByteArrayOutputStream();
                    byte[] bytes = new byte[1024];
                    int len = -1;
                    while((len=bis.read(bytes))!=-1){
                        baos.write(bytes,len);
                    }
                    bis.close();
                    baos.close();
                    conn.disconnect();
                }
                if (baos!=null){
                    bitmap = decodeSampledBitmapFromStream(baos.toByteArray(),300,200);
                    addBitmapToCache(params[0],bitmap);//添加到内存缓存
                    editor = diskLruCache.edit(key);
                    //关键
                    bitmap.compress(Bitmap.CompressFormat.JPEG,100,editor.newOutputStream(0));
                    editor.commit();//提交
                }
            } catch (IOException e) {
                try {
                    editor.abort();//放弃写入
                } catch (IOException e1) {
                    e1.printStackTrace();
                }
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
            callBack.response(bitmap);
        }
    }.execute(url);
}

DiskLruCache 缓存的获取

//获取磁盘缓存
public InputStream getDiskCache(String url) {
    Log.i(TAG,"getDiskCache...");
    String key = hashKeyForDisk(url);
    try {
        DiskLruCache.Snapshot snapshot = diskLruCache.get(key);
        if (snapshot!=null){
            return snapshot.getInputStream(0);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

//MainActivity.java
public class MainActivity extends AppCompatActivity {
    private static final String TAG = "cache_test";
    public static String CACHE_DIR = "diskCache";  //缓存目录
    public static int CACHE_SIZE = 1024 * 1024 * 10; //缓存大小
    private ImageView imageView;
    private LruCache<String,String> lruCache;
    private LruCacheUtils cacheUtils;
    private String url = "http://img06.tooopen.com/images/20161012/tooopen_sy_181713275376.jpg";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageView = (ImageView) findViewById(R.id.imageView);
    }
    
    @Override
    protected void onResume() {
        super.onResume();
        cacheUtils = LruCacheUtils.getInstance();
        //创建内存缓存和磁盘缓存
        cacheUtils.createCache(this,CACHE_DIR,CACHE_SIZE);
    }
    
    @Override
    protected void onPause() {
        super.onPause();
        cacheUtils.flush();
    }

    @Override
    protected void onStop() {
        super.onStop();
        cacheUtils.close();
    }
    
    public void loadImage(View view){
        load(url,imageView);
    }
    
    public void removeLruCache(View view){
        Log.i(TAG,"移出内存缓存...");
        cacheUtils.removeLruCache(url);
    }
    
    public void removeDiskLruCache(View view){
        Log.i(TAG,"移出磁盘缓存...");
        cacheUtils.removeDiskLruCache(url);
    }
    
    private void load(String url,final ImageView imageView){
        //从内存中获取图片
        Bitmap bitmap = cacheUtils.getBitmapFromCache(url);
        if (bitmap == null){
            //从磁盘中获取图片
            InputStream is = cacheUtils.getDiskCache(url);
            if (is == null){
                //从网络上获取图片
                cacheUtils.putCache(url,new LruCacheUtils.CallBack<Bitmap>() {
                    @Override
                    public void response(Bitmap bitmap1) {
                        Log.i(TAG,"从网络中获取图片...");
                        Log.i(TAG,"正在从网络中下载图片...");
                        imageView.setImageBitmap(bitmap1);
                        Log.i(TAG,"从网络中获取图片成功...");
                    }
                });
            }else{
                Log.i(TAG,"从磁盘中获取图片...");
                bitmap = BitmapFactory.decodeStream(is);
                imageView.setImageBitmap(bitmap);
            }
        }else{
            Log.i(TAG,"从内存中获取图片...");
            imageView.setImageBitmap(bitmap);
        }
    }
}