android图片缓存管理

文章来自：http://keegan-lee.diandian.com/post/2012-12-06/40047548955

多写了点注释而已，没有其他的变化，只有两级，硬引用和软引用，感觉已经够了吧，没用到弱引用

public class ImageFileCache {
    // 目录名称
    private static final String CACHDIR = "ImgCach";
    // 图片缓存后缀
    private static final String WHOLESALE_CONV = ".cach";
    // 10mb
    private static final int MB = 1024 * 1024;
    // 10张图片
    private static final int CACHE_SIZE = 10;
    // 
    private static final int FREE_SD_SPACE_NEEDED_TO_CACHE = 10;

    public ImageFileCache() {
        // 清理文件缓存
        removeCache(getDirectory());
    }

    /** 从缓存中获取图片 **/
    public Bitmap getImage(final String url) {
        final String path = getDirectory() + "/" + convertUrlToFileName(url);
        File file = new File(path);
        if (file.exists()) {
            Bitmap bmp = BitmapFactory.decodeFile(path);
            if (bmp == null) {
                file.delete();
            } else {
                updateFileTime(path);
                return bmp;
            }
        }
        return null;
    }

    /** 将图片存入文件缓存 **/
    public void saveBitmap(Bitmap bm, String url) {
        // bitmap == null直接返回
        if (bm == null) {
            return;
        }
        // 判断sdcard上的空间
        if (FREE_SD_SPACE_NEEDED_TO_CACHE > freeSpaceOnSd()) {
            // SD空间不足
            return;
        }
        String filename = convertUrlToFileName(url);
        String dir = getDirectory();
        File dirFile = new File(dir);
        // 缓存目录不存在，创建目录
        if (!dirFile.exists())
            dirFile.mkdirs();
        // 构造文件实例
        File file = new File(dir + "/" + filename);
        try {
            // 创建该文件
            file.createNewFile();
            // 以该文件构造输出流
            OutputStream outStream = new FileOutputStream(file);
            // 将该bitmap写入到outStream输出流
            bm.compress(Bitmap.CompressFormat.JPEG, 100, outStream);
            outStream.flush();
            outStream.close();
        } catch (FileNotFoundException e) {
            Log.w("ImageFileCache", "FileNotFoundException");
        } catch (IOException e) {
            Log.w("ImageFileCache", "IOException");
        }
    }

    /**
     * 计算存储目录下的文件大小，
     * 当文件总大小大于规定的CACHE_SIZE或者sdcard剩余空间小于FREE_SD_SPACE_NEEDED_TO_CACHE的规定
     * 那么删除40%最近没有被使用的文件
     */
    private boolean removeCache(String dirPath) {
        // 以路径dirPath构造File实例
        File dir = new File(dirPath);
        // 图片文件数组， dir不是路径时，返回null
        File[] files = dir.listFiles();
        // 
        if (files == null) {
            return true;
        }
        // sd卡的存储状态必须可读可写，否则返回false
        if (!android.os.Environment.getExternalStorageState().equals(
                android.os.Environment.MEDIA_MOUNTED)) {
            return false;
        }

        int dirSize = 0;
        for (int i = 0; i < files.length; i++) {
            // 判断该文件名是否存在WHOLESALE_CONV后缀
            // 存在则获取文件长度，长度为0说明文件不存在
            if (files[i].getName().contains(WHOLESALE_CONV)) {
                dirSize += files[i].length();
            }
        }
        
        // 如果总文件长度大于CACHE_SIZE * MB（10mb）|| 当前 freeSpaceOnSd() < 10mb
        if (dirSize > CACHE_SIZE * MB
                || FREE_SD_SPACE_NEEDED_TO_CACHE > freeSpaceOnSd()) {
            // 要移除的文件个数
            int removeFactor = (int) ((0.4 * files.length) + 1);
            // 根据文件修改时间排序
            Arrays.sort(files, new FileLastModifSort());
            for (int i = 0; i < removeFactor; i++) {
                if (files[i].getName().contains(WHOLESALE_CONV)) {
                    files[i].delete();
                }
            }
        }

        // 如果sd卡剩余空间 <= 10mb
        if (freeSpaceOnSd() <= CACHE_SIZE) {
            return false;
        }

        return true;
    }

    /** 修改文件的最后修改时间 **/
    public void updateFileTime(String path) {
        File file = new File(path);
        long newModifiedTime = System.currentTimeMillis();
        file.setLastModified(newModifiedTime);
    }

    /** 计算sdcard上的剩余空间 **/
    private int freeSpaceOnSd() {
        // StatFs查询文件系统相关的信息。
        StatFs stat = new StatFs(Environment.getExternalStorageDirectory()
                .getPath());
        double sdFreeMB = ((double) stat.getAvailableBlocks() * (double) stat
                .getBlockSize()) / MB;
        return (int) sdFreeMB;
    }

    /** 将url转成文件名 **/
    private String convertUrlToFileName(String url) {
        String[] strs = url.split("/");
        return strs[strs.length - 1] + WHOLESALE_CONV;
    }

    /** 获得缓存目录 **/
    private String getDirectory() {
        String dir = getSDPath() + "/" + CACHDIR;
        return dir;
    }

    /** 取SD卡路径 **/
    private String getSDPath() {
        File sdDir = null;
        // getExternalStorageState() 获得当前外部储存媒体的状态。
        // MEDIA_MOUNTED 存储媒体已经挂载，并且挂载点可读/写。
        boolean sdCardExist = Environment.getExternalStorageState().equals(
                android.os.Environment.MEDIA_MOUNTED); // 判断sd卡是否存在
        if (sdCardExist) {
            // getExternalStorageDirectory() 获取外部存储媒体目录
            sdDir = Environment.getExternalStorageDirectory(); // 获取根目录
        }
        if (sdDir != null) {
            return sdDir.toString();
        } else {
            return "";
        }
    }

    /**
     * 根据文件的最后修改时间进行排序
     */
    private class FileLastModifSort implements Comparator<File> {
        public int compare(File arg0, File arg1) {
            if (arg0.lastModified() > arg1.lastModified()) {
                return 1;
            } else if (arg0.lastModified() == arg1.lastModified()) {
                return 0;
            } else {
                return -1;
            }
        }
    }

}

public class ImageMemoryCache {
    /**
     * 从内存读取数据速度是最快的，为了更大限度使用内存，这里使用了两层缓存。
     * 硬引用缓存不会轻易被回收，用来保存常用数据，不常用的转入软引用缓存。
     */
    private static final int SOFT_CACHE_SIZE = 15;  //软引用缓存容量
    private static LruCache<String, Bitmap> mLruCache;  //硬引用缓存
    private static LinkedHashMap<String, SoftReference<Bitmap>> mSoftCache;  //软引用缓存
                                                                                          
    public ImageMemoryCache(Context context) {
        // 通过ActivityManager获取应用的可用内存大小，单位mb
        int memClass = ((ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE)).getMemoryClass();
        // 硬引用缓存容量
        int cacheSize = 1024 * 1024 * memClass / 4;  //硬引用缓存容量，为系统可用内存的1/4
        
        mLruCache = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap value) {
                if (value != null)
                    return value.getRowBytes() * value.getHeight();
                else
                    return 0;
            }
                                                                                          
            @Override
            protected void entryRemoved(boolean evicted, String key, Bitmap oldValue, Bitmap newValue) {
                if (oldValue != null)
                    // 硬引用缓存容量满的时候，会根据LRU算法把最近没有被使用的图片转入此软引用缓存
                    mSoftCache.put(key, new SoftReference<Bitmap>(oldValue));
            }
        };
        mSoftCache = new LinkedHashMap<String, SoftReference<Bitmap>>(SOFT_CACHE_SIZE, 0.75f, true) {
            private static final long serialVersionUID = 6040103833179403725L;
            @Override
            protected boolean removeEldestEntry(Entry<String, SoftReference<Bitmap>> eldest) {
                if (size() > SOFT_CACHE_SIZE){    
                    return true;  
                }  
                return false; 
            }
        };
    }
                                                                                  
    /**
     * 从缓存中获取图片
     */
    public Bitmap getBitmapFromCache(String url) {
        Bitmap bitmap;
        //先从硬引用缓存中获取
        synchronized (mLruCache) {
            bitmap = mLruCache.get(url);
            if (bitmap != null) {
                //如果找到的话，把元素移到LinkedHashMap的最前面，从而保证在LRU算法中是最后被删除
                mLruCache.remove(url);
                mLruCache.put(url, bitmap);
                return bitmap;
            }
        }
        //如果硬引用缓存中找不到，到软引用缓存中找
        synchronized (mSoftCache) { 
            SoftReference<Bitmap> bitmapReference = mSoftCache.get(url);
            if (bitmapReference != null) {
                bitmap = bitmapReference.get();
                if (bitmap != null) {
                    //将图片移回硬缓存
                    mLruCache.put(url, bitmap);
                    mSoftCache.remove(url);
                    return bitmap;
                } else {
                    mSoftCache.remove(url);
                }
            }
        }
        return null;
    } 
                                                                                  
    /**
     * 添加图片到缓存
     */
    public void addBitmapToCache(String url, Bitmap bitmap) {
        if (bitmap != null) {
            synchronized (mLruCache) {
                mLruCache.put(url, bitmap);
            }
        }
    }
                                                                                  
    public void clearCache() {
        mSoftCache.clear();
    }
}

package bitmap.cache;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;

public class ImageGetFromHttp {
    private static final String LOG_TAG = "ImageGetFromHttp";
                                                           
    public static Bitmap downloadBitmap(String url) {
        final HttpClient client = new DefaultHttpClient();
        final HttpGet getRequest = new HttpGet(url);
                                                               
        try {
            HttpResponse response = client.execute(getRequest);
            final int statusCode = response.getStatusLine().getStatusCode();
            if (statusCode != HttpStatus.SC_OK) {
                Log.w(LOG_TAG, "Error " + statusCode + " while retrieving bitmap from " + url);
                return null;
            }
                                                                   
            final HttpEntity entity = response.getEntity();
            if (entity != null) {
                InputStream inputStream = null;
                try {
                    inputStream = entity.getContent();
                    FilterInputStream fit = new FlushedInputStream(inputStream);
                    return BitmapFactory.decodeStream(fit);
                } finally {
                    if (inputStream != null) {
                        inputStream.close();
                        inputStream = null;
                    }
                    entity.consumeContent();
                }
            }
        } catch (IOException e) {
            getRequest.abort();
            Log.w(LOG_TAG, "I/O error while retrieving bitmap from " + url, e);
        } catch (IllegalStateException e) {
            getRequest.abort();
            Log.w(LOG_TAG, "Incorrect URL: " + url);
        } catch (Exception e) {
            getRequest.abort();
            Log.w(LOG_TAG, "Error while retrieving bitmap from " + url, e);
        } finally {
            client.getConnectionManager().shutdown();
        }
        return null;
    }
                                                       
    /*
     * An InputStream that skips the exact number of bytes provided, unless it reaches EOF.
     */
    static class FlushedInputStream extends FilterInputStream {
        public FlushedInputStream(InputStream inputStream) {
            super(inputStream);
        }
                                                       
        @Override
        public long skip(long n) throws IOException {
            long totalBytesSkipped = 0L;
            while (totalBytesSkipped < n) {
                long bytesSkipped = in.skip(n - totalBytesSkipped);
                if (bytesSkipped == 0L) {
                    int b = read();
                    if (b < 0) {
                        break;  // we reached EOF
                    } else {
                        bytesSkipped = 1; // we read one byte
                    }
                }
                totalBytesSkipped += bytesSkipped;
            }
            return totalBytesSkipped;
        }
    }
}

public class GetBitmap {
    /*** 获得一张图片,从三个地方获取,首先是内存缓存,然后是文件缓存,最后从网络获取 ***/
    public static Bitmap getBitmap(String url) {
        // 从内存缓存中获取图片
        Bitmap result = TestApp.memoryCache.getBitmapFromCache(url);
        if (result == null) {
            // 文件缓存中获取
            result = TestApp.fileCache.getImage(url);
            if (result == null) {
                // 从网络获取
                result = ImageGetFromHttp.downloadBitmap(url);
                if (result != null) {
                    TestApp.fileCache.saveBitmap(result, url);
                    TestApp.memoryCache.addBitmapToCache(url, result);
                }
            } else {
                // 添加到内存缓存
                TestApp.memoryCache.addBitmapToCache(url, result);
            }
        }
        return result;
    }
}