Android缓存之DiskLruCache磁盘缓存的使用

public final class DiskLruCache implements Closeable {

 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_TEMP);
  this.journalFileBackup = new File(directory, JOURNAL_FILE_BACKUP);
  this.valueCount = valueCount;
  this.maxSize = maxSize;
 }

 //四个参数分别为，1.缓存的路径目录 2.版本号 3.每个节点对应的数据个数，4.缓存的大小，10 * 1024 * 1024 = 10M
      DiskLruCache diskLruCache = DiskLruCache.open(getCachFile(context, uniqueName), 1, 1, cacheSize);

/**
   * 获取缓存目录
   *
   * @param context
   * @param uniqueName 指定目录下的文件名
   */
  private File getCachFile(Context context, String uniqueName) {
    String catchPath;
    //有内存卡，并且内存卡没有正在移除，就把文件缓存到内存卡中
    if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !Environment.isExternalStorageRemovable()) {
      catchPath = context.getExternalCacheDir().getPath();
    } else {
      catchPath = context.getCacheDir().getPath();
    }
    return new File(catchPath + File.separator + uniqueName);
  }

new Thread() {
          @Override
          public void run() {
            DiskLruCache.Editor editor = null;
            try {
              //创建 Editor 对象
              editor = diskLruCache.edit(hashKeyForDisk(url));
              if (editor != null) {
                //创建输出流
                OutputStream outputStream = editor.newOutputStream(0);
                //url 也就是 下载图片的地址
                //outputStream 的作用在于，
                //从网络下载图片的时候，图片通过该输出流写到文件系统，
                //也就是说，图片下载到了磁盘缓存中。
                if (downloadUrlToStream(url, outputStream)) {
                  editor.commit();
                } else {
                  //释放编辑锁
                  editor.abort();
                }
                diskLruCache.flush();
              }

            } catch (Exception e) {
              e.printStackTrace();
            }

          }
        }.start();

 /**
   * 将key进行加密
   *
   * @param key
   * @return
   */
  public String hashKeyForDisk(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;
  }

  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();
  }

OutputStream outputStream = editor.newOutputStream(0);

 //也就是说，图片下载到了磁盘缓存中。
                if (downloadUrlToStream(url, outputStream)) {
                  editor.commit();
                } else {
                  //释放编辑锁
                  editor.abort();
                }
                diskLruCache.flush();

/**
   * 从网络中下载图片，并写到缓存中
   *
   * @param urlString
   * @param outputStream
   * @return
   */
  private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
    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(), 8 * 1024);
      out = new BufferedOutputStream(outputStream, 8 * 1024);
      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;
  }

 DiskLruCache.Snapshot snapshot = diskLruCache.get(hashKeyForDisk(url));
        if(snapshot!=null){
          InputStream inputStream = snapshot.getInputStream(0);
          Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
          //如果不为空，则直接展示缓存中的bitmap
          imageView.setImageBitmap(bitmap); 
        }

public synchronized boolean remove(String key) throws IOException