android编程实现图片库的封装方法

public class PictureLibrary {
 /*
  * 图片库的操作
  */
 File file;
 URL url;
 HttpURLConnection conn;
 InputStream is;
 FileOutputStream fos;
 private Lock lock = new ReentrantLock();
 private Condition downFile = lock.newCondition();
 // 通过URL将数据下载到本地操作
 private String toLocalFile(String strURL) {
  String fileName = Utils.getFileName(strURL);
  String path = Environment.getExternalStorageDirectory() + "/"
    + EcologicalTourism.FILE_PATH + "/images/" + fileName;
  return path;
 }
 // 通过URL将数据下载到本地临时文件中
 private String toLocalFileTemp(String strURL) {
  String s = Utils.getFileName(strURL);
  String fileName = s+"temp";
  String path_url = Environment.getExternalStorageDirectory() + "/"
    + EcologicalTourism.FILE_PATH + "/tempimages/" + fileName;
  return path_url;
 }
 /*
  * 保存图片到本地，并返回本地url（此函数是阻塞的）
  * main
  * @参数：strURL，参数为图片的URL.返回值：该图片在本地SD卡暂存的位置
  * 函数的工作是负责将图片从互联网上取得，存在本地存储中，并返回本地存储的文件路径，供调用者直接使用。如果文件已经存在本地，直接返回
  * 如果文件未在本地，则直接从服务器下载，函数阻塞。
  */
 public String getReadSD(String strURL) {
  Log.i("test", "拿到网络的地址是：" + strURL);
  String strLocalFile = toLocalFile(strURL); //k：把服务器URL转换为本地URL
  String strLocalFileTemp = toLocalFileTemp(strURL); //k：把服务器URL转换为本地临时URL
  while (true) {
   File file = new File(strLocalFile);
   Log.i("test", "本地文件是：" + strLocalFile);
   File tfile = new File(strLocalFileTemp);
   Log.i("test", "临时文件是：" + strLocalFileTemp);
   // 1上锁
   lock.lock();
   if (file.exists()) {
    // 2if 本地文件存在
    // 解锁
    // 返回本地路径
    lock.unlock();
    Log.i("test", "返回本地路径：" + file);
    return strLocalFile;
   } else if (tfile.exists()) {
    // if 对应的暂存文件存在
    // 解锁
    lock.unlock();
    try {
     // 睡眠
     downFile.await();
    } catch (Exception e) {
      e.printStackTrace();
     Log.i("test", "e 出现了异常1" + e);
    }
   } else {
    try {
     // 创建对应的暂存文件
     tfile.createNewFile();
    } catch (IOException e) {
     Log.i("test", "e 出现了异常2" + e);
    }
    // 解锁
    lock.unlock();
    // 下载文件内容到暂存文件中
    downURL2(strURL, strLocalFile);
    // 上锁
    lock.lock();
    // 修改暂存文件名字为本地文件名
    tfile.renameTo(file);
    // 解锁
    lock.unlock();
   }
  }
 }
 private void downURL2(String strURL, String strLocalFileTemp) {
  // TODO Auto-generated method stub
  URL url;
  try {
   url = new URL(strURL);
   HttpURLConnection conn = (HttpURLConnection) url.openConnection();
   conn.setConnectTimeout(5000);
   conn.setRequestMethod("GET");
   conn.setDoInput(true);
   if (conn.getResponseCode() == 200) {
     InputStream is = conn.getInputStream();
     FileOutputStream fos = new FileOutputStream(strLocalFileTemp);
     byte[] buffer = new byte[1024];
     int len = 0;
     while ((len = is.read(buffer)) != -1) {
       fos.write(buffer, 0, len);
     }
     is.close();
     fos.close();
     // 返回一个URI对象
   }
  } catch (MalformedURLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (ProtocolException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
 /*
  * 阻塞式下载url到文件 toFile中
  */
 private boolean downURL(String strURL, String toFile) {
  URL url;
  try {
   url = new URL(strURL);
   HttpURLConnection httpUrl = (HttpURLConnection) url
     .openConnection();
   httpUrl.setRequestMethod("GET");
   int fileSize = httpUrl.getContentLength();// 文件大小
   httpUrl.disconnect();// 关闭连接
   int threadSize = 6;// 默认设置6个线程
   threadSize = fileSize % threadSize == 0 ? threadSize
     : threadSize + 1;
   int currentSize = fileSize / threadSize; // 每条线程下载大小
   String dowloadir = Environment.getExternalStorageDirectory() + "/"
     + EcologicalTourism.FILE_PATH + "/images/";
   File dir = new File(dowloadir);
   if (!dir.exists()) {
    dir.mkdirs();
   }
   File file = new File(dir, toFile);
   RandomAccessFile randomFile = new RandomAccessFile(file, "rw");
   randomFile.setLength(fileSize);// 指定 file 文件的大小
   for (int i = 0; i < threadSize; i++) {
    int startposition = i * currentSize;// 每条线程开始写入文件的位置
    RandomAccessFile threadFile = new RandomAccessFile(file, "rw");
    Log.i("syso", "toFile的内容是：" + toFile);
    threadFile.seek(startposition);
    new DownLoadThread(i, currentSize, threadFile, startposition,
      url).start();
   }
  } catch (Exception e) {
   e.printStackTrace();
   Log.i("syso", "download下载失败" + e);
  }
  return true;
 }
 /**
  * 实现线程下载
  * 
  */
 private static class DownLoadThread extends Thread {
  @SuppressWarnings("unused")
  private int threadId;// 线程编号
  private int currentSize;// 每条线程的大小
  private RandomAccessFile threadFile; // 每条线程 要写入文件类
  private int startposition;// 每条线程开始写入文件的位置
  private URL url; //网络地址
  public DownLoadThread(int threadId, int currentSize,
    RandomAccessFile threadFile, int startposition, URL url) {
   this.threadId = threadId;
   this.currentSize = currentSize;
   this.threadFile = threadFile;
   this.startposition = startposition;
   this.url = url;
  }
  public void run() {
   try {
    HttpURLConnection httpUrl = (HttpURLConnection) url
      .openConnection();
    httpUrl.setRequestMethod("GET");
    httpUrl.setRequestProperty("range", "bytes=" + startposition
      + "-");// 指定服务器的位置
    InputStream is = httpUrl.getInputStream();
    byte[] data = new byte[1024];
    int len = -1;
    int threadFileSize = 0;
    while ((threadFileSize < currentSize)
      && ((len = is.read(data)) != -1)) {
     threadFile.write(data, 0, len);
     threadFileSize += len;
    }
    httpUrl.disconnect();
    is.close();
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
 }
 /**
 * 从本缓存中获取图片
 */
 public Bitmap getBitmapFromCache(String imageURL) {
 // String bitmapName = imageURL.substring(imageURL.lastIndexOf("/") + 1); 
  String bitmapName = Utils.getFileName(imageURL);
  File cacheDir = new File(Environment.getExternalStorageDirectory() + "/"
    + EcologicalTourism.FILE_PATH + "/images/");
  File[] cacheFiles = cacheDir.listFiles();
  int i = 0;
  if(null!=cacheFiles){
   for(; i<cacheFiles.length;i++){
    if(bitmapName.equals(cacheFiles[i].getName())){
     break;
    }
   }
   if(i < cacheFiles.length)
   {
    return BitmapFactory.decodeFile(Environment.getExternalStorageDirectory() + "/"
      + EcologicalTourism.FILE_PATH + "/images/" + bitmapName);
   }
  }
  return null;
 }