Android 图片加载缓存

package com.wangdong.bitmapcache;

import android.graphics.Bitmap;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.Adapter;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.RelativeLayout;

import java.util.HashSet;
import java.util.Set;

/**
 * 下面我通过一个例子来演示一下 LruCache 内存缓存 和 DisLruCache 本地缓存 的使用
 *
 * 主要功能就是一个用 GridView 来展示大量的网络图片, 因为GridView 有服用机制,
 *     1.滑出屏幕的 ImageView 持有的图片进行回收,再将 ImagView 指定新的图片,从而避免了OOM
 *     2.同时在 ImageView 加载图片是我们使用了内存 和 硬盘进行双缓存
 *     3.每一个图片的加载和显示任务都运行在独立的线程（异步任务）中，除非这个图片缓存在 LruCache 中，这种情况下图片会立即显示。
 *     4.如果需要的图片缓存在 DiskLruCache，也会开启一个独立的线程队列。如果在缓存中都没有正确的图片，任务线程会从网络下载。
 *
 *     注意:如果是自定义 View 来实现照片墙,没有复用机制的话，那么需要在 ImageView 滑出屏幕后手动回收图片，
 *     即将ImageView加载一张默认空图片，从而切断与之前图片的引用，让系统可以回收之前图片，避免OOM。
 *
 */
public class MainActivity extends AppCompatActivity implements AbsListView.OnScrollListener {

    private GridView gridview;
    private BitmapCaChe bitmapCache;//LruCache 内存缓存
    private BitmapDiskCache bitmapDiskCache; //本地存储卡缓存

    private Set taskCollection; //图片下载任务

    private int mFirstVisibleItem;
    private int mVisibleItemCount;
    private boolean isFirstEnter = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        bitmapCache = new BitmapCaChe(); //创建 LruCache 内存缓存
        bitmapDiskCache = new BitmapDiskCache(this); //创建 DisLruCache 本地缓存

        taskCollection = new HashSet(); //创建下载任务集合

        gridview = (GridView) findViewById(R.id.gridview); //初始GridView控件
        gridview.setAdapter(new Adapter()); //GridView设置Adapter
        gridview.setOnScrollListener(this); //设置GridView 滑动监听
    }

    /**OnScrollListener 滚动接口回调之调用结束时
     *
     * @param view  正在报告其滚动状态的视图
     * @param firstVisibleItem 第一个可见单元格的索引(忽略如果visibleItemCount=0)
     * @param visibleItemCount  可见item数
     * @param totalItemCount 列表适配器中的总项数。
     */
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        mFirstVisibleItem = firstVisibleItem;
        mVisibleItemCount = visibleItemCount;
        // 下载的任务应该由onScrollStateChanged里调用，但首次进入程序时onScrollStateChanged并不会调用，
        // 因此在这里为首次进入程序开启下载任务。
        if (isFirstEnter && visibleItemCount > 0) {
            loadBitmaps(firstVisibleItem, visibleItemCount);
            isFirstEnter = false;
        }
    }

    /**OnScrollListener 滚动接口回调之触发时候
     *
     * @param view 正在报告其滚动状态的视图。
     * @param scrollState  当前滚动状态。
     *                    SCROLL_STATE_FLING用户之前一直在使用触摸滚动，并进行了一次狂欢。
     *                     SCROLL_STATE_IDLE视图不是滚动的。
     *                     SCROLL_STATE_TOUCH_SCROLL用户正在使用触摸滚动，他们的手指仍然在屏幕上。
     */
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // 仅当GridView静止时才去下载图片，GridView滑动时取消所有正在下载的任务
        if (scrollState == SCROLL_STATE_IDLE) { //停止滚动
            loadBitmaps(mFirstVisibleItem, mVisibleItemCount); //下载图片
        } else {
            cancelAllTasks();  //开始滚动停止下载图片
        }
    }

    private void loadBitmaps(int firstVisibleItem, int visibleItemCount) {
        try {
            for (int i = firstVisibleItem; i < firstVisibleItem + visibleItemCount; i++) {
                String imageUrl = Images.imageUrls[i];
                BitmapDownloadTask task = new BitmapDownloadTask();
                taskCollection.add(task);
                task.execute(imageUrl);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public int dip2px(float dipValue) {
        final float scale = getResources().getDisplayMetrics().density;
        return (int) (dipValue * scale + 0.5f);
    }

    public void showlog(String info) {
        System.out.print("LRU " + info + "\n");
    }

    public void cancelAllTasks() {
        if (taskCollection != null) {
            for (BitmapDownloadTask task : taskCollection) {
                task.cancel(false);
            }
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        bitmapDiskCache.flush();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        bitmapDiskCache.close();
    }




    /**首先继承AsyncTask<开始参数类型,后天执行参数类型,结果返回参数类型*/
    class BitmapDownloadTask extends AsyncTask {

        private String imageUrl;

        /*执行异步任务代码处理*/
        @Override
        protected Bitmap doInBackground(String... params) {
            imageUrl = params[0];//获取图片网址
            Bitmap bitmap = bitmapDiskCache.getBitmapFromDiskCache(imageUrl);//获取
            if (bitmap != null) {
                bitmapCache.addBitmapToMemoryCache(imageUrl, bitmap);
                return bitmap;
            } else {
                bitmapDiskCache.downloadBitmapToDiskCache(imageUrl, new BitmapDiskCache.DownloadListener() {
                    @Override
                    public void downloadSuccess(Bitmap bitmap) {
                        bitmapCache.addBitmapToMemoryCache(imageUrl, bitmap);
                    }
                    @Override
                    public void downloadFail() {
                    }
                });
                return bitmapDiskCache.getBitmapFromDiskCache(imageUrl);
            }
        }
        //ui线程执行
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
            ImageView imageView = (ImageView) gridview.findViewWithTag(imageUrl);
            //通过Tag找到对应的ImageView，如果ImageView滑出屏幕，则返回null
            if (imageView != null && bitmap != null) {
                imageView.setImageBitmap(bitmap);
            }
            taskCollection.remove(this);
        }
    }

    /**
     * 适配器 Adapter
     */
    public class Adapter extends BaseAdapter {

        @Override
        public int getCount() {
            return Images.imageUrls.length;
        }

        @Override
        public String getItem(int position) {
            return Images.imageUrls[position];
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder viewHolder = null;
            if(convertView == null) {
                viewHolder = new ViewHolder();
                convertView = LayoutInflater.from(MainActivity.this).inflate(R.layout.image_item, null);
                viewHolder.image = (ImageView) convertView.findViewById(R.id.img);
                convertView.setTag(viewHolder);
            } else {
                viewHolder = (ViewHolder)convertView.getTag();
            }
            //
            RelativeLayout.LayoutParams pra = (RelativeLayout.LayoutParams) viewHolder.image.getLayoutParams();//获取布局参数
            //item中imageview控件布局 高 等于 :(Gridview的宽 减去 2dp*2 )除以3
            pra.height = (gridview.getWidth() - 2*dip2px(2)) / 3;
            //然后再把布局参数设置给 item中ImagView控件
            viewHolder.image.setLayoutParams(pra);//这样就可以让GridView中每个Item适配所有手机屏幕 显示正方形的图片


            //获取数据
            String imageUrl = getItem(position);

            //给每个ImageView设置唯一的tag，防止图片加载错乱

         /* ListView、GridView都有两个方法setTag/findViewWithTag，简单的说就是给Item中的View设置一个唯一的Tag值，
         之后可以通过这个Tag值找到与其对应的View，因为ListView和GridView都有复用机制，所以当Item被滑出屏幕后，有可能会被复用，
         Item中的View也就被设置了另外一个Tag值，所以这时通过之前的Tag寻找View返回的是null。
         这里给ImageView设置了一个唯一Tag值，就是待加载图片的url，之后图片下载完成，再通过这个Tag找到ImageView，
         如果ImageView为null，说明图片已经滑出了屏幕，此时不再加载，否则ImageView加载刚刚下载完成的图片，
         这样防止了下载好的图片加载到别的ImageView而形成错乱。 */

            viewHolder.image.setTag(imageUrl);

            //通过图片HTTP网址作为key值获取内存中缓存bitmap
            Bitmap bitmap = bitmapCache.getBitmapFromMemCache(imageUrl);
            //如果内存缓存中没有为null值
            if (bitmap != null) {
                //如果内存缓存中获取bitmap不为null 就设置显示
                viewHolder.image.setImageBitmap(bitmap);
            } else {
                //否则显示默认系统本地图片
                viewHolder.image.setImageResource(R.drawable.error);
            }
            return convertView;
        }

        public class ViewHolder {
            public ImageView image;
        }

    }
}

public class Images {

   public final static String[] imageUrls = new String[] {
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        "http://b226.photo.store.qq.com/psb?/V13dV9iu45C4on/t7i4ojNEchzmj8oVvS3Ww8gShvnCNxJVU6eWvwptngk!/b/dLSUv4ajKgAA&bo=gALgAQAAAAABF1M!&rf=viewer_4",
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        "http://b167.photo.store.qq.com/psb?/V13dV9iu2Ug5tr/VY8NcdtZePxle1mn1FXPbadOH.XSqHGU8uScoWezUEo!/b/dCtXkGOkAgAA&bo=IAMWAgAAAAABJzc!&rf=viewer_4",
        "http://b232.photo.store.qq.com/psb?/V13dV9iu2Ug5tr/*RIQpwoj97vmihjQCyoJwX2xHvhimVrMqjePgm5rfP4!/b/dDj4SYqMGwAA&bo=IAMVAgAAAAABFwQ!&rf=viewer_4",
        "http://b228.photo.store.qq.com/psb?/V13dV9iu2Ug5tr/gahu96xz4UXJPkHGv.NVP2DbR9F8urUtvEtrZHtMv.c!/b/dNvR84dHCwAA&bo=wAOAAgAAAAAKF3o!&rf=viewer_4",
        "http://b162.photo.store.qq.com/psb?/V13dV9iu2Ug5tr/ynza6fgyZqqXjcPh9px*ZnhZUhQplwPXE5dEaTsom4Q!/b/dHrfk2BuIwAA&bo=3QJXAgAAAAABF7o!&rf=viewer_4",
        "http://b162.photo.store.qq.com/psb?/V13dV9iu2Ug5tr/H2dN0YjxgWQtyXlWs06ueEDbanylPVNf*h1UVeqrdzk!/b/dKudnmAYHQAA&bo=4QLzAgAAAAABJxI!&rf=viewer_4"
 };
   
}

/**
 * 本地 缓存
 */
public class BitmapDiskCache {

    private DiskLruCache mDiskLruCache = null;

    //
    public BitmapDiskCache(Context context) {
        try {
            File cacheDir = getDiskCacheDir(context, "bitmap");
            if (!cacheDir.exists()) {
                cacheDir.mkdirs();
            }
            mDiskLruCache = DiskLruCache.open(cacheDir, getAppVersion(context), 1, 10 * 1024 * 1024);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 本地缓存路径
     * @param context   环境变量
     * @param uniqueName 文件名称
     * @return {File}
     */
    public File getDiskCacheDir(Context context, String uniqueName) {
        String cachePath;
        /**
         * 判断SD卡是否挂载,和存在
         */
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !Environment.isExternalStorageRemovable()) {
            //获取sd卡的缓存文件地址
            cachePath = context.getExternalCacheDir().getPath();
        } else {
            //获取应用下缓存地址
            cachePath = context.getCacheDir().getPath();
        }
        /**
         * 在缓存文件下创建自定义命名的文件夹并返回File
         */
        return new File(cachePath + File.separator + uniqueName);
    }

    /**
     * 通过应用管理获取应用 版本code号
     * @param context
     * @return
     */
    public int getAppVersion(Context context) {
        try {
            PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
            return info.versionCode;
        } catch (PackageManager.NameNotFoundException e) {
            e.printStackTrace();
        }
        return 1;
    }

    //因为涉及下载，需要在线程中执行此方法
    public void downloadBitmapToDiskCache(String imageUrl, DownloadListener mDownloadListener) {
        try {
            String key = getMD5String(imageUrl);
            DiskLruCache.Editor editor = mDiskLruCache.edit(key);
            if (editor != null) {
                OutputStream outputStream = editor.newOutputStream(0);
                if (downloadUrlToStream(imageUrl, outputStream)) {
                    editor.commit();
                    if (mDownloadListener != null) {
                        Bitmap bmp = getBitmapFromDiskCache(imageUrl);
                        mDownloadListener.downloadSuccess(bmp);
                    }
                } else {
                    editor.abort();
                    if (mDownloadListener != null) {
                        mDownloadListener.downloadFail();
                    }
                }
            }
          mDiskLruCache.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * MD5加密
     * @param key
     * @return
     */
    public String getMD5String(String key) {
        String cacheKey;
        try {
            final MessageDigest mDigest = MessageDigest.getInstance("MD5");
            mDigest.update(key.getBytes());
            cacheKey = bytesToHexString(mDigest.digest());
        } catch (NoSuchAlgorithmException e) {
            cacheKey = String.valueOf(key.hashCode());
        }
        return cacheKey;
    }

    /**
     *  字节 转 16进制 转 String
     * @param bytes
     * @return
     */
    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();
    }

    private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
        //系统版本高 HttpURLConnection 使用回报错 需要在清单文件中添加 android:usesCleartextTraffic="true"
        HttpURLConnection urlConnection = null;
        BufferedOutputStream out = null;
        BufferedInputStream in = null;
        try {
            final URL url = new URL(urlString);
            urlConnection = (HttpURLConnection) url.openConnection();
            in = new BufferedInputStream(urlConnection.getInputStream());
            out = new BufferedOutputStream(outputStream);
            int b;
            while ((b = in.read()) != -1) {
                out.write(b);
            }
            return true;
        } catch (final IOException e) {
            e.printStackTrace();
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            try {
                if (out != null) {
                    out.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (final IOException e) {
                e.printStackTrace();
            }
        }
        return false;
    }

    /**
     * 获取本地缓存中的图片
     * @param imageUrl 通过图片的url
     * @return
     */
    public Bitmap getBitmapFromDiskCache(String imageUrl) {
        try {
            String key = getMD5String(imageUrl);
            DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);
            if (snapShot != null) {
                InputStream is = snapShot.getInputStream(0);
                Bitmap bitmap = BitmapFactory.decodeStream(is);
                return bitmap;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 移除 指定的imageUrl的图片
     * @param imageUrl
     * @return
     */
    public boolean removeBitmapFromDiskCache(String imageUrl) {
        try {
            String key = getMD5String(imageUrl);
            return mDiskLruCache.remove(key);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;
    }

    /**
     * 清空本地图片缓存
     */
    public void removeAll() {
        try {
            mDiskLruCache.delete();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 获取本地缓存 图片个数
     */
    public void getAllSize() {
        mDiskLruCache.size();
    }

    public void flush() {
        try {
            mDiskLruCache.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void close() {
        try {
            mDiskLruCache.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public interface DownloadListener {
        public void downloadSuccess(Bitmap bitmap);
        public void downloadFail();
    }
}

public class BitmapCaChe {

    private LruCache mMemoryCache;

    public BitmapCaChe() {
        //获取到可用内存的最大值,使用内存超出这个值会引起OutofMemory异常
        int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        // 使用最大可用内存值的1/8作为缓存的大小。
        int cacheSize = maxMemory / 8;
        mMemoryCache = new LruCache(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap bitmap) {
                // 重写此方法来衡量每张图片的大小，默认返回图片数量。
                return bitmap.getByteCount() / 1024;
            }
        };
    }
    /**
     * 添加图片
     * 如果内存缓存中没有就添加到内存缓存中如果有就不执行 key判断
     */
    public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
        if (getBitmapFromMemCache(key) == null) {
            mMemoryCache.put(key, bitmap);
        }
    }

    /**
     *  获取内存缓存中的图片并返回,
     *  如果就没就通过 LruCache 内部方法 创建返回null值
     *             V createdValue = create(key);
     *             if (createdValue == null) {
     *            return null;
     *         }
     * @param key
     * @return
     */
    public Bitmap getBitmapFromMemCache(String key) {
        return mMemoryCache.get(key);
    }

}

/**
 ******************************************************************************
 * Taken from the JB source code, can be found in:
 * libcore/luni/src/main/java/libcore/io/DiskLruCache.java
 * or direct link:
 * https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java
 ******************************************************************************
 *
 * A cache that uses a bounded amount of space on a filesystem. Each cache
 * entry has a string key and a fixed number of values. Values are byte
 * sequences, accessible as streams or files. Each value must be between {@code
 * 0} and {@code Integer.MAX_VALUE} bytes in length.
 *
 * 
The cache stores its data in a directory on the filesystem. This
 * directory must be exclusive to the cache; the cache may delete or overwrite
 * files from its directory. It is an error for multiple processes to use the
 * same cache directory at the same time.
 *
 * 
This cache limits the number of bytes that it will store on the
 * filesystem. When the number of stored bytes exceeds the limit, the cache will
 * remove entries in the background until the limit is satisfied. The limit is
 * not strict: the cache may temporarily exceed it while waiting for files to be
 * deleted. The limit does not include filesystem overhead or the cache
 * journal so space-sensitive applications should set a conservative limit.
 *
 * 
Clients call {@link #edit} to create or update the values of an entry. An
 * entry may have only one editor at one time; if a value is not available to be
 * edited then {@link #edit} will return null.
 * 

 *     
When an entry is being created it is necessary to
 *         supply a full set of values; the empty value should be used as a
 *         placeholder if necessary.
 *     
When an entry is being edited, it is not necessary
 *         to supply data for every value; values default to their previous
 *         value.
 * 
 * Every {@link #edit} call must be matched by a call to {@link Editor#commit}
 * or {@link Editor#abort}. Committing is atomic: a read observes the full set
 * of values as they were before or after the commit, but never a mix of values.
 *
 * 
Clients call {@link #get} to read a snapshot of an entry. The read will
 * observe the value at the time that {@link #get} was called. Updates and
 * removals after the call do not impact ongoing reads.
 *
 * 
This class is tolerant of some I/O errors. If files are missing from the
 * filesystem, the corresponding entries will be dropped from the cache. If
 * an error occurs while writing a cache value, the edit will fail silently.
 * Callers should handle other problems by catching {@code IOException} and
 * responding appropriately.
 */
public final class DiskLruCache implements Closeable {
    static final String JOURNAL_FILE = "journal";
    static final String JOURNAL_FILE_TMP = "journal.tmp";
    static final String MAGIC = "libcore.io.DiskLruCache";
    static final String VERSION_1 = "1";
    static final long ANY_SEQUENCE_NUMBER = -1;
    private static final String CLEAN = "CLEAN";
    private static final String DIRTY = "DIRTY";
    private static final String REMOVE = "REMOVE";
    private static final String READ = "READ";

    private static final Charset UTF_8 = Charset.forName("UTF-8");
    private static final int IO_BUFFER_SIZE = 8 * 1024;

    /*
     * This cache uses a journal file named "journal". A typical journal file
     * looks like this:
     *     libcore.io.DiskLruCache
     *     1
     *     100
     *     2
     *
     *     CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054
     *     DIRTY 335c4c6028171cfddfbaae1a9c313c52
     *     CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342
     *     REMOVE 335c4c6028171cfddfbaae1a9c313c52
     *     DIRTY 1ab96a171faeeee38496d8b330771a7a
     *     CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234
     *     READ 335c4c6028171cfddfbaae1a9c313c52
     *     READ 3400330d1dfc7f3f7f4b8d4d803dfcf6
     *
     * The first five lines of the journal form its header. They are the
     * constant string "libcore.io.DiskLruCache", the disk cache's version,
     * the application's version, the value count, and a blank line.
     *
     * Each of the subsequent lines in the file is a record of the state of a
     * cache entry. Each line contains space-separated values: a state, a key,
     * and optional state-specific values.
     *   o DIRTY lines track that an entry is actively being created or updated.
     *     Every successful DIRTY action should be followed by a CLEAN or REMOVE
     *     action. DIRTY lines without a matching CLEAN or REMOVE indicate that
     *     temporary files may need to be deleted.
     *   o CLEAN lines track a cache entry that has been successfully published
     *     and may be read. A publish line is followed by the lengths of each of
     *     its values.
     *   o READ lines track accesses for LRU.
     *   o REMOVE lines track entries that have been deleted.
     *
     * The journal file is appended to as cache operations occur. The journal may
     * occasionally be compacted by dropping redundant lines. A temporary file named
     * "journal.tmp" will be used during compaction; that file should be deleted if
     * it exists when the cache is opened.
     */

    private final File directory;
    private final File journalFile;
    private final File journalFileTmp;
    private final int appVersion;
    private final long maxSize;
    private final int valueCount;
    private long size = 0;
    private Writer journalWriter;
    private final LinkedHashMap lruEntries
            = new LinkedHashMap(0, 0.75f, true);
    private int redundantOpCount;

    /**
     * To differentiate between old and current snapshots, each entry is given
     * a sequence number each time an edit is committed. A snapshot is stale if
     * its sequence number is not equal to its entry's sequence number.
     */
    private long nextSequenceNumber = 0;

    /* From java.util.Arrays */
    @SuppressWarnings("unchecked")
    private static  T[] copyOfRange(T[] original, int start, int end) {
        final int originalLength = original.length; // For exception priority compatibility.
        if (start > end) {
            throw new IllegalArgumentException();
        }
        if (start < 0 || start > originalLength) {
            throw new ArrayIndexOutOfBoundsException();
        }
        final int resultLength = end - start;
        final int copyLength = Math.min(resultLength, originalLength - start);
        final T[] result = (T[]) Array
                .newInstance(original.getClass().getComponentType(), resultLength);
        System.arraycopy(original, start, result, 0, copyLength);
        return result;
    }

    /**
     * Returns the remainder of 'reader' as a string, closing it when done.
     */
    public static String readFully(Reader reader) throws IOException {
        try {
            StringWriter writer = new StringWriter();
            char[] buffer = new char[1024];
            int count;
            while ((count = reader.read(buffer)) != -1) {
                writer.write(buffer, 0, count);
            }
            return writer.toString();
        } finally {
            reader.close();
        }
    }

    /**
     * Returns the ASCII characters up to but not including the next "\r\n", or
     * "\n".
     *
     * @throws EOFException if the stream is exhausted before the next newline
     *     character.
     */
    public static String readAsciiLine(InputStream in) throws IOException {
        // TODO: support UTF-8 here instead

        StringBuilder result = new StringBuilder(80);
        while (true) {
            int c = in.read();
            if (c == -1) {
                throw new EOFException();
            } else if (c == '\n') {
                break;
            }

            result.append((char) c);
        }
        int length = result.length();
        if (length > 0 && result.charAt(length - 1) == '\r') {
            result.setLength(length - 1);
        }
        return result.toString();
    }

    /**
     * Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null.
     */
    public static void closeQuietly(Closeable closeable) {
        if (closeable != null) {
            try {
                closeable.close();
            } catch (RuntimeException rethrown) {
                throw rethrown;
            } catch (Exception ignored) {
            }
        }
    }

    /**
     * Recursively delete everything in {@code dir}.
     */
    // TODO: this should specify paths as Strings rather than as Files
    public static void deleteContents(File dir) throws IOException {
        File[] files = dir.listFiles();
        if (files == null) {
            throw new IllegalArgumentException("not a directory: " + dir);
        }
        for (File file : files) {
            if (file.isDirectory()) {
                deleteContents(file);
            }
            if (!file.delete()) {
                throw new IOException("failed to delete file: " + file);
            }
        }
    }

    /** This cache uses a single background thread to evict entries. */
    private final ExecutorService executorService = new ThreadPoolExecutor(0, 1,
            60L, TimeUnit.SECONDS, new LinkedBlockingQueue());
    private final Callable cleanupCallable = new Callable() {
        @Override
        public Void call() throws Exception {
            synchronized (DiskLruCache.this) {
                if (journalWriter == null) {
                    return null; // closed
                }
                trimToSize();
                if (journalRebuildRequired()) {
                    rebuildJournal();
                    redundantOpCount = 0;
                }
            }
            return null;
        }
    };

    private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {
        this.directory = directory;
        this.appVersion = appVersion;
        this.journalFile = new File(directory, JOURNAL_FILE);
        this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);
        this.valueCount = valueCount;
        this.maxSize = maxSize;
    }

    /**
     * Opens the cache in {@code directory}, creating a cache if none exists
     * there.
     *
     * @param directory a writable directory
     * @param appVersion
     * @param valueCount the number of values per cache entry. Must be positive.
     * @param maxSize the maximum number of bytes this cache should use to store
     * @throws IOException if reading or writing the cache directory fails
     */
    public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)
            throws IOException {
        if (maxSize <= 0) {
            throw new IllegalArgumentException("maxSize <= 0");
        }
        if (valueCount <= 0) {
            throw new IllegalArgumentException("valueCount <= 0");
        }

        // prefer to pick up where we left off
        DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
        if (cache.journalFile.exists()) {
            try {
                cache.readJournal();
                cache.processJournal();
                cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true),
                        IO_BUFFER_SIZE);
                return cache;
            } catch (IOException journalIsCorrupt) {
//                System.logW("DiskLruCache " + directory + " is corrupt: "
//                        + journalIsCorrupt.getMessage() + ", removing");
                cache.delete();
            }
        }

        // create a new empty cache
        directory.mkdirs();
        cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
        cache.rebuildJournal();
        return cache;
    }

    private void readJournal() throws IOException {
        InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE);
        try {
            String magic = readAsciiLine(in);
            String version = readAsciiLine(in);
            String appVersionString = readAsciiLine(in);
            String valueCountString = readAsciiLine(in);
            String blank = readAsciiLine(in);
            if (!MAGIC.equals(magic)
                    || !VERSION_1.equals(version)
                    || !Integer.toString(appVersion).equals(appVersionString)
                    || !Integer.toString(valueCount).equals(valueCountString)
                    || !"".equals(blank)) {
                throw new IOException("unexpected journal header: ["
                        + magic + ", " + version + ", " + valueCountString + ", " + blank + "]");
            }

            while (true) {
                try {
                    readJournalLine(readAsciiLine(in));
                } catch (EOFException endOfJournal) {
                    break;
                }
            }
        } finally {
            closeQuietly(in);
        }
    }

    private void readJournalLine(String line) throws IOException {
        String[] parts = line.split(" ");
        if (parts.length < 2) {
            throw new IOException("unexpected journal line: " + line);
        }

        String key = parts[1];
        if (parts[0].equals(REMOVE) && parts.length == 2) {
            lruEntries.remove(key);
            return;
        }

        Entry entry = lruEntries.get(key);
        if (entry == null) {
            entry = new Entry(key);
            lruEntries.put(key, entry);
        }

        if (parts[0].equals(CLEAN) && parts.length == 2 + valueCount) {
            entry.readable = true;
            entry.currentEditor = null;
            entry.setLengths(copyOfRange(parts, 2, parts.length));
        } else if (parts[0].equals(DIRTY) && parts.length == 2) {
            entry.currentEditor = new Editor(entry);
        } else if (parts[0].equals(READ) && parts.length == 2) {
            // this work was already done by calling lruEntries.get()
        } else {
            throw new IOException("unexpected journal line: " + line);
        }
    }

    /**
     * Computes the initial size and collects garbage as a part of opening the
     * cache. Dirty entries are assumed to be inconsistent and will be deleted.
     */
    private void processJournal() throws IOException {
        deleteIfExists(journalFileTmp);
        for (Iterator i = lruEntries.values().iterator(); i.hasNext(); ) {
            Entry entry = i.next();
            if (entry.currentEditor == null) {
                for (int t = 0; t < valueCount; t++) {
                    size += entry.lengths[t];
                }
            } else {
                entry.currentEditor = null;
                for (int t = 0; t < valueCount; t++) {
                    deleteIfExists(entry.getCleanFile(t));
                    deleteIfExists(entry.getDirtyFile(t));
                }
                i.remove();
            }
        }
    }

    /**
     * Creates a new journal that omits redundant information. This replaces the
     * current journal if it exists.
     */
    private synchronized void rebuildJournal() throws IOException {
        if (journalWriter != null) {
            journalWriter.close();
        }

        Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE);
        writer.write(MAGIC);
        writer.write("\n");
        writer.write(VERSION_1);
        writer.write("\n");
        writer.write(Integer.toString(appVersion));
        writer.write("\n");
        writer.write(Integer.toString(valueCount));
        writer.write("\n");
        writer.write("\n");

        for (Entry entry : lruEntries.values()) {
            if (entry.currentEditor != null) {
                writer.write(DIRTY + ' ' + entry.key + '\n');
            } else {
                writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
            }
        }

        writer.close();
        journalFileTmp.renameTo(journalFile);
        journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE);
    }

    private static void deleteIfExists(File file) throws IOException {
//        try {
//            Libcore.os.remove(file.getPath());
//        } catch (ErrnoException errnoException) {
//            if (errnoException.errno != OsConstants.ENOENT) {
//                throw errnoException.rethrowAsIOException();
//            }
//        }
        if (file.exists() && !file.delete()) {
            throw new IOException();
        }
    }

    /**
     * Returns a snapshot of the entry named {@code key}, or null if it doesn't
     * exist is not currently readable. If a value is returned, it is moved to
     * the head of the LRU queue.
     */
    public synchronized Snapshot get(String key) throws IOException {
        checkNotClosed();
        validateKey(key);
        Entry entry = lruEntries.get(key);
        if (entry == null) {
            return null;
        }

        if (!entry.readable) {
            return null;
        }

        /*
         * Open all streams eagerly to guarantee that we see a single published
         * snapshot. If we opened streams lazily then the streams could come
         * from different edits.
         */
        InputStream[] ins = new InputStream[valueCount];
        try {
            for (int i = 0; i < valueCount; i++) {
                ins[i] = new FileInputStream(entry.getCleanFile(i));
            }
        } catch (FileNotFoundException e) {
            // a file must have been deleted manually!
            return null;
        }

        redundantOpCount++;
        journalWriter.append(READ + ' ' + key + '\n');
        if (journalRebuildRequired()) {
            executorService.submit(cleanupCallable);
        }

        return new Snapshot(key, entry.sequenceNumber, ins);
    }

    /**
     * Returns an editor for the entry named {@code key}, or null if another
     * edit is in progress.
     */
    public Editor edit(String key) throws IOException {
        return edit(key, ANY_SEQUENCE_NUMBER);
    }

    private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {
        checkNotClosed();
        validateKey(key);
        Entry entry = lruEntries.get(key);
        if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER
                && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {
            return null; // snapshot is stale
        }
        if (entry == null) {
            entry = new Entry(key);
            lruEntries.put(key, entry);
        } else if (entry.currentEditor != null) {
            return null; // another edit is in progress
        }

        Editor editor = new Editor(entry);
        entry.currentEditor = editor;

        // flush the journal before creating files to prevent file leaks
        journalWriter.write(DIRTY + ' ' + key + '\n');
        journalWriter.flush();
        return editor;
    }

    /**
     * Returns the directory where this cache stores its data.
     */
    public File getDirectory() {
        return directory;
    }

    /**
     * Returns the maximum number of bytes that this cache should use to store
     * its data.
     */
    public long maxSize() {
        return maxSize;
    }

    /**
     * Returns the number of bytes currently being used to store the values in
     * this cache. This may be greater than the max size if a background
     * deletion is pending.
     */
    public synchronized long size() {
        return size;
    }

    private synchronized void completeEdit(Editor editor, boolean success) throws IOException {
        Entry entry = editor.entry;
        if (entry.currentEditor != editor) {
            throw new IllegalStateException();
        }

        // if this edit is creating the entry for the first time, every index must have a value
        if (success && !entry.readable) {
            for (int i = 0; i < valueCount; i++) {
                if (!entry.getDirtyFile(i).exists()) {
                    editor.abort();
                    throw new IllegalStateException("edit didn't create file " + i);
                }
            }
        }

        for (int i = 0; i < valueCount; i++) {
            File dirty = entry.getDirtyFile(i);
            if (success) {
                if (dirty.exists()) {
                    File clean = entry.getCleanFile(i);
                    dirty.renameTo(clean);
                    long oldLength = entry.lengths[i];
                    long newLength = clean.length();
                    entry.lengths[i] = newLength;
                    size = size - oldLength + newLength;
                }
            } else {
                deleteIfExists(dirty);
            }
        }

        redundantOpCount++;
        entry.currentEditor = null;
        if (entry.readable | success) {
            entry.readable = true;
            journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
            if (success) {
                entry.sequenceNumber = nextSequenceNumber++;
            }
        } else {
            lruEntries.remove(entry.key);
            journalWriter.write(REMOVE + ' ' + entry.key + '\n');
        }

        if (size > maxSize || journalRebuildRequired()) {
            executorService.submit(cleanupCallable);
        }
    }

    /**
     * We only rebuild the journal when it will halve the size of the journal
     * and eliminate at least 2000 ops.
     */
    private boolean journalRebuildRequired() {
        final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;
        return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD
                && redundantOpCount >= lruEntries.size();
    }

    /**
     * Drops the entry for {@code key} if it exists and can be removed. Entries
     * actively being edited cannot be removed.
     *
     * @return true if an entry was removed.
     */
    public synchronized boolean remove(String key) throws IOException {
        checkNotClosed();
        validateKey(key);
        Entry entry = lruEntries.get(key);
        if (entry == null || entry.currentEditor != null) {
            return false;
        }

        for (int i = 0; i < valueCount; i++) {
            File file = entry.getCleanFile(i);
            if (!file.delete()) {
                throw new IOException("failed to delete " + file);
            }
            size -= entry.lengths[i];
            entry.lengths[i] = 0;
        }

        redundantOpCount++;
        journalWriter.append(REMOVE + ' ' + key + '\n');
        lruEntries.remove(key);

        if (journalRebuildRequired()) {
            executorService.submit(cleanupCallable);
        }

        return true;
    }

    /**
     * Returns true if this cache has been closed.
     */
    public boolean isClosed() {
        return journalWriter == null;
    }

    private void checkNotClosed() {
        if (journalWriter == null) {
            throw new IllegalStateException("cache is closed");
        }
    }

    /**
     * Force buffered operations to the filesystem.
     */
    public synchronized void flush() throws IOException {
        checkNotClosed();
        trimToSize();
        journalWriter.flush();
    }

    /**
     * Closes this cache. Stored values will remain on the filesystem.
     */
    public synchronized void close() throws IOException {
        if (journalWriter == null) {
            return; // already closed
        }
        for (Entry entry : new ArrayList(lruEntries.values())) {
            if (entry.currentEditor != null) {
                entry.currentEditor.abort();
            }
        }
        trimToSize();
        journalWriter.close();
        journalWriter = null;
    }

    private void trimToSize() throws IOException {
        while (size > maxSize) {
//            Map.Entry toEvict = lruEntries.eldest();
            final Map.Entry toEvict = lruEntries.entrySet().iterator().next();
            remove(toEvict.getKey());
        }
    }

    /**
     * Closes the cache and deletes all of its stored values. This will delete
     * all files in the cache directory including files that weren't created by
     * the cache.
     */
    public void delete() throws IOException {
        close();
        deleteContents(directory);
    }

    private void validateKey(String key) {
        if (key.contains(" ") || key.contains("\n") || key.contains("\r")) {
            throw new IllegalArgumentException(
                    "keys must not contain spaces or newlines: \"" + key + "\"");
        }
    }

    private static String inputStreamToString(InputStream in) throws IOException {
        return readFully(new InputStreamReader(in, UTF_8));
    }

    /**
     * A snapshot of the values for an entry.
     */
    public final class Snapshot implements Closeable {
        private final String key;
        private final long sequenceNumber;
        private final InputStream[] ins;

        private Snapshot(String key, long sequenceNumber, InputStream[] ins) {
            this.key = key;
            this.sequenceNumber = sequenceNumber;
            this.ins = ins;
        }

        /**
         * Returns an editor for this snapshot's entry, or null if either the
         * entry has changed since this snapshot was created or if another edit
         * is in progress.
         */
        public Editor edit() throws IOException {
            return DiskLruCache.this.edit(key, sequenceNumber);
        }

        /**
         * Returns the unbuffered stream with the value for {@code index}.
         */
        public InputStream getInputStream(int index) {
            return ins[index];
        }

        /**
         * Returns the string value for {@code index}.
         */
        public String getString(int index) throws IOException {
            return inputStreamToString(getInputStream(index));
        }

        @Override
        public void close() {
            for (InputStream in : ins) {
                closeQuietly(in);
            }
        }
    }

    /**
     * Edits the values for an entry.
     */
    public final class Editor {
        private final Entry entry;
        private boolean hasErrors;

        private Editor(Entry entry) {
            this.entry = entry;
        }

        /**
         * Returns an unbuffered input stream to read the last committed value,
         * or null if no value has been committed.
         */
        public InputStream newInputStream(int index) throws IOException {
            synchronized (DiskLruCache.this) {
                if (entry.currentEditor != this) {
                    throw new IllegalStateException();
                }
                if (!entry.readable) {
                    return null;
                }
                return new FileInputStream(entry.getCleanFile(index));
            }
        }

        /**
         * Returns the last committed value as a string, or null if no value
         * has been committed.
         */
        public String getString(int index) throws IOException {
            InputStream in = newInputStream(index);
            return in != null ? inputStreamToString(in) : null;
        }

        /**
         * Returns a new unbuffered output stream to write the value at
         * {@code index}. If the underlying output stream encounters errors
         * when writing to the filesystem, this edit will be aborted when
         * {@link #commit} is called. The returned output stream does not throw
         * IOExceptions.
         */
        public OutputStream newOutputStream(int index) throws IOException {
            synchronized (DiskLruCache.this) {
                if (entry.currentEditor != this) {
                    throw new IllegalStateException();
                }
                return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));
            }
        }

        /**
         * Sets the value at {@code index} to {@code value}.
         */
        public void set(int index, String value) throws IOException {
            Writer writer = null;
            try {
                writer = new OutputStreamWriter(newOutputStream(index), UTF_8);
                writer.write(value);
            } finally {
                closeQuietly(writer);
            }
        }

        /**
         * Commits this edit so it is visible to readers.  This releases the
         * edit lock so another edit may be started on the same key.
         */
        public void commit() throws IOException {
            if (hasErrors) {
                completeEdit(this, false);
                remove(entry.key); // the previous entry is stale
            } else {
                completeEdit(this, true);
            }
        }

        /**
         * Aborts this edit. This releases the edit lock so another edit may be
         * started on the same key.
         */
        public void abort() throws IOException {
            completeEdit(this, false);
        }

        private class FaultHidingOutputStream extends FilterOutputStream {
            private FaultHidingOutputStream(OutputStream out) {
                super(out);
            }

            @Override
            public void write(int oneByte) {
                try {
                    out.write(oneByte);
                } catch (IOException e) {
                    hasErrors = true;
                }
            }

            @Override
            public void write(byte[] buffer, int offset, int length) {
                try {
                    out.write(buffer, offset, length);
                } catch (IOException e) {
                    hasErrors = true;
                }
            }

            @Override
            public void close() {
                try {
                    out.close();
                } catch (IOException e) {
                    hasErrors = true;
                }
            }

            @Override
            public void flush() {
                try {
                    out.flush();
                } catch (IOException e) {
                    hasErrors = true;
                }
            }
        }
    }

    private final class Entry {
        private final String key;

        /** Lengths of this entry's files. */
        private final long[] lengths;

        /** True if this entry has ever been published */
        private boolean readable;

        /** The ongoing edit or null if this entry is not being edited. */
        private Editor currentEditor;

        /** The sequence number of the most recently committed edit to this entry. */
        private long sequenceNumber;

        private Entry(String key) {
            this.key = key;
            this.lengths = new long[valueCount];
        }

        public String getLengths() throws IOException {
            StringBuilder result = new StringBuilder();
            for (long size : lengths) {
                result.append(' ').append(size);
            }
            return result.toString();
        }

        /**
         * Set lengths using decimal numbers like "10123".
         */
        private void setLengths(String[] strings) throws IOException {
            if (strings.length != valueCount) {
                throw invalidLengths(strings);
            }

            try {
                for (int i = 0; i < strings.length; i++) {
                    lengths[i] = Long.parseLong(strings[i]);
                }
            } catch (NumberFormatException e) {
                throw invalidLengths(strings);
            }
        }

        private IOException invalidLengths(String[] strings) throws IOException {
            throw new IOException("unexpected journal line: " + Arrays.toString(strings));
        }

        public File getCleanFile(int i) {
            return new File(directory, key + "." + i);
        }

        public File getDirtyFile(int i) {
            return new File(directory, key + "." + i + ".tmp");
        }
    }
}