Android_异步加载网络图片并缓存到本地

1、Android 异步加载网络图片并缓存到本地摘要：在android应用开发的时候，加载网络图片是一个非常重要的部分，很多图片不可能放在本地，所以就必须要从服务器或者网络读取图片。在android应用开发的时候，加载网络图片是一个非常重要的部分，很多图片不可能放在本地，所以就必须要从服务器或者网络读取图片。软引用是一个现在非常流行的方法，用户体验比较好，不用每次都需要从网络下载图片，如果下载后就存到本地，下次读取时首先查看本地有没有，如果没有再从网络读取。记得2月份在和爱奇艺公司的项目总监一起搞联通的OTT盒子的时候他就提了一下软引用，奇艺做的手机客户端就是采用这种方法，所以你会发现奇艺客户端占

2、用很大的空间，下面就分享一下异步加载网络图片的方法吧。FileCache.javajava view plaincopy .import java.io.File; .import android.content.Context; .public class FileCache .private File cacheDir; .public FileCache(Context context) ./ 找一个用来缓存图片的路径 .if (android.os.Environment.getExternalStorageState().equals( .android.os.Environment

3、.MEDIA_MOUNTED) .cacheDir = new File(android.os.Environment.getExternalStorageDirectory(), .文件夹名称); .else .cacheDir = context.getCacheDir(); .if (!cacheDir.exists() .cacheDir.mkdirs(); . .public File getFile(String url) .String filename = String.valueOf(url.hashCode(); .File f = new File(cacheDir, f

4、ilename); .return f; . .public void clear() .File files = cacheDir.listFiles(); .if (files = null) .return; .for (File f : files) .f.delete(); . . .HttpUtil.javajava view plaincopy .import java.io.ByteArrayOutputStream; .import java.io.File; .import java.io.FileNotFoundException; .import java.io.Fil

5、eOutputStream; .import java.io.IOException; .import java.io.InputStream; .import java.io.OutputStream; .import java.io.UnsupportedEncodingException; .import .HttpURLConnection; .import .MalformedURLException; .import .ProtocolException; .import .URL; .import .

6、URLEncoder; .import java.util.Map; ./* .* Http 请求工具类 .* .* author Scorpio.Liu .* .*/ .public class HttpUtil ./* .* 获取响应字符串 .* .* param path .* 路径 .* param parameters .* 参数 .* return 响应字符串 .*/ .public static String getResponseStr(String path, Map parameters) .StringBuffer buffer = new StringBuffer();

7、 .URL url; .try .if (parameters != null & !parameters.isEmpty() .for (Map.Entry entry : parameters.entrySet() ./ 完成转码操作 .buffer.append(entry.getKey().append(=) .append(URLEncoder.encode(entry.getValue(), UTF-8).append(&); . .buffer.deleteCharAt(buffer.length() - 1); . .url = new URL(path); .HttpURLC

8、onnection urlConnection = (HttpURLConnection) url.openConnection(); .urlConnection.setConnectTimeout(3000); .urlConnection.setRequestMethod(POST); .urlConnection.setDoInput(true);/ 表示从服务器获取数据 .urlConnection.setDoOutput(true);/ 表示向服务器写数据 ./ 获得上传信息的字节大小以及长度 .byte mydata = buffer.toString().getBytes();

9、 ./ 表示设置请求体的类型是文本类型 .urlConnection.setRequestProperty(Content-Type, .application/x-www-form-urlencoded); .urlConnection.setRequestProperty(Content-Length, String.valueOf(mydata.length); ./ 获得输出流,向服务器输出数据 .OutputStream outputStream = urlConnection.getOutputStream(); .outputStream.write(mydata, 0, myd

10、ata.length); .outputStream.close(); .int responseCode = urlConnection.getResponseCode(); .if (responseCode = 200) .return changeInputStream(urlConnection.getInputStream(); . . catch (UnsupportedEncodingException e) .e.printStackTrace(); . catch (MalformedURLException e) .e.printStackTrace(); . catch

11、 (ProtocolException e) .e.printStackTrace(); . catch (IOException e) .e.printStackTrace(); . .return null; . .private static String changeInputStream(InputStream inputStream) .ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); .byte data = new byte1024; .int len = 0; .String result =

12、; .if (inputStream != null) .try .while (len = inputStream.read(data) != -1) .outputStream.write(data, 0, len); . .result = new String(outputStream.toByteArray(), UTF-8); . catch (IOException e) .e.printStackTrace(); . . .return result; . .public static InputStream getInputStream(String path) .URL u

13、rl; .try .url = new URL(path); .HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); .urlConnection.setConnectTimeout(3000); .urlConnection.setRequestMethod(GET); .urlConnection.setDoInput(true);/ 表示从服务器获取数据 .urlConnection.connect(); .if (urlConnection.getResponseCode() = 200)

14、 .return urlConnection.getInputStream(); . catch (MalformedURLException e) ./ TODO Auto-generated catch block .e.printStackTrace(); . catch (IOException e) ./ TODO Auto-generated catch block .e.printStackTrace(); . catch (Exception e) ./ TODO Auto-generated catch block .e.printStackTrace(); . .retur

15、n null; . .public static byte readStream(InputStream inStream) throws Exception .ByteArrayOutputStream outSteam = new ByteArrayOutputStream(); .byte buffer = new byte1024; .int len = -1; .while (len = inStream.read(buffer) != -1) .outSteam.write(buffer, 0, len); . .outSteam.close(); .inStream.close(

16、); .return outSteam.toByteArray(); . .public static void CopyStream(String url, File f) .FileOutputStream fileOutputStream = null; .InputStream inputStream = null; .try .inputStream = getInputStream(url); .byte data = new byte1024; .int len = 0; .fileOutputStream = new FileOutputStream(f); .while (l

17、en = inputStream.read(data) != -1) .fileOutputStream.write(data, 0, len); . . catch (FileNotFoundException e) .e.printStackTrace(); . catch (IOException e) .e.printStackTrace(); . finally .if (inputStream != null) .try .inputStream.close(); . catch (IOException e) .e.printStackTrace(); . . .if (file

18、OutputStream != null) .try .fileOutputStream.close(); . catch (IOException e) .e.printStackTrace(); . . . . . .MemoryCache.javajava view plaincopy .import java.lang.ref.SoftReference; .import java.util.Collections; .import java.util.HashMap; .import java.util.Map; .import android.graphics.Bitmap; .p

19、ublic class MemoryCache .private MapString, SoftReference cache = Collections .synchronizedMap(new HashMapString, SoftReference();/ 软引用 .public Bitmap get(String id) .if (!cache.containsKey(id) .return null; .SoftReference ref = cache.get(id); .return ref.get(); . .public void put(String id, Bitmap

20、bitmap) .cache.put(id, new SoftReference(bitmap); . .public void clear() .cache.clear(); . . .ImageLoader.javajava view plaincopy .import java.io.File; .import java.io.FileInputStream; .import java.io.FileNotFoundException; .import java.io.UnsupportedEncodingException; .import .URLEncoder; .

21、import java.util.Collections; .import java.util.Map; .import java.util.WeakHashMap; .import java.util.concurrent.ExecutorService; .import java.util.concurrent.Executors; .import android.app.Activity; .import android.content.Context; .import android.graphics.Bitmap; .import android.graphics.BitmapFac

22、tory; .import android.graphics.drawable.BitmapDrawable; .import android.widget.ImageView; .public class ImageLoader .private MemoryCache memoryCache = new MemoryCache(); .private FileCache fileCache; .private Map imageViews = Collections .synchronizedMap(new WeakHashMap(); .private ExecutorService e

23、xecutorService; .private boolean isSrc; ./* .* param context .* 上下文对象 .* param flag .* true为source资源，false为background资源 .*/ .public ImageLoader(Context context, boolean flag) .fileCache = new FileCache(context); .executorService = Executors.newFixedThreadPool(5); .isSrc = flag; . .final int stub_id

24、= R.drawable.ic_launcher; .public void DisplayImage(String url, ImageView imageView) .String u1 = url.substring(0, url.lastIndexOf(/) + 1); .String u2 = url.substring(url.lastIndexOf(/) + 1); .try .u2 = URLEncoder.encode(u2, UTF-8); . catch (UnsupportedEncodingException e) .e.printStackTrace(); . .u

25、rl = u1 + u2; .imageViews.put(imageView, url); .Bitmap bitmap = memoryCache.get(url); .if (bitmap != null) .if (isSrc) .imageView.setImageBitmap(bitmap); .else .imageView.setBackgroundDrawable(new BitmapDrawable(bitmap); . else .queuePhoto(url, imageView); .if (isSrc) .imageView.setImageResource(stu

26、b_id); .else .imageView.setBackgroundResource(stub_id); . . .private void queuePhoto(String url, ImageView imageView) .PhotoToLoad p = new PhotoToLoad(url, imageView); .executorService.submit(new PhotosLoader(p); . .private Bitmap getBitmap(String url) .try .File f = fileCache.getFile(url); ./ 从sd卡

27、.Bitmap b = onDecodeFile(f); .if (b != null) .return b; ./ 从网络 .Bitmap bitmap = null; .System.out.println(ImageLoader-download); .HttpUtil.CopyStream(url, f); .bitmap = onDecodeFile(f); .return bitmap; . catch (Exception ex) .ex.printStackTrace(); .return null; . . .public Bitmap onDecodeFile(File f

28、) .try .return BitmapFactory.decodeStream(new FileInputStream(f); . catch (FileNotFoundException e) ./ TODO Auto-generated catch block .e.printStackTrace(); . .return null; . ./* .* 解码图像用来减少内存消耗 .* .* param f .* return .*/ .public Bitmap decodeFile(File f) .try ./ 解码图像大小 .BitmapFactory.Options o = n

29、ew BitmapFactory.Options(); .o.inJustDecodeBounds = true; .BitmapFactory.decodeStream(new FileInputStream(f), null, o); ./ 找到正确的刻度值，它应该是2的幂。 .final int REQUIRED_SIZE = 70; .int width_tmp = o.outWidth, height_tmp = o.outHeight; .int scale = 1; .while (true) .if (width_tmp / 2 REQUIRED_SIZE | height_t

30、mp / 2 REQUIRED_SIZE) .break; .width_tmp /= 2; .height_tmp /= 2; .scale *= 2; . .BitmapFactory.Options o2 = new BitmapFactory.Options(); .o2.inSampleSize = scale; .return BitmapFactory.decodeStream(new FileInputStream(f), null, o2); . catch (FileNotFoundException e) . .return null; . ./* .* 任务队列 .*

31、.* author Scorpio.Liu .* .*/ .private class PhotoToLoad .public String url; .public ImageView imageView; .public PhotoToLoad(String u, ImageView i) .url = u; .imageView = i; . . .class PhotosLoader implements Runnable .PhotoToLoad photoToLoad; .PhotosLoader(PhotoToLoad photoToLoad) .this.photoToLoad = photoToLoad; . .Override .public void run() .if (imageViewReused(photoToLoad) .return; .Bitmap bmp = getBitmap(photoToLoad.url); .memoryCache.put(photoToLoad.url, b