大家在做安卓应用的时候 经常要从网络中获取图片 都是通过URL去获取 可是如果本地有图片数据 从本地获取数据不更加快一些 自己在工作中遇到这个问题 所以采用了一个URL和本地图片的一个映射关系 先从本地区获取 假如本地没有再从网络中获取 本方法考虑到多线程问题 欢迎大家一起共同探讨！
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;
}