Android实现图片异步加载并缓存到本地

概述在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。

下面就分享一下异步加载网络图片的方法吧。

fileCache.java

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.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,filename);     return f;   }    public voID clear() {     file[] files = cacheDir.Listfiles();     if (files == null)       return;     for (file f : files)       f.delete();   }  }

 httpUtil.java

import java.io.ByteArrayOutputStream; import java.io.file; import java.io.fileNotFoundException; import java.io.fileOutputStream; import java.io.IOException; import java.io.inputStream; import java.io.OutputStream; import java.io.UnsupportedEnCodingException; import java.net.httpURLConnection; import java.net.MalformedURLException; import java.net.ProtocolException; import java.net.URL; import java.net.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<String,String> parameters) {     StringBuffer buffer = new StringBuffer();     URL url;     try {       if (parameters != null && !parameters.isEmpty()) {         for (Map.Entry<String,String> entry : parameters.entrySet()) {           // 完成转码 *** 作           buffer.append(entry.getKey()).append("=")               .append(URLEncoder.encode(entry.getValue(),"UTF-8")).append("&");         }         buffer.deleteCharat(buffer.length() - 1);       }       url = new URL(path);       httpURLConnection 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();       // 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,mydata.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 (ProtocolException e) {       e.printstacktrace();     } catch (IOException e) {       e.printstacktrace();     }     return null;   }    private static String changeinputStream(inputStream inputStream) {     ByteArrayOutputStream outputStream = new ByteArrayOutputStream();     byte[] data = new byte[1024];     int len = 0;     String result = "";     if (inputStream != null) {       try {         while ((len = inputStream.read(data)) != -1) {           outputStream.write(data,len);         }         result = new String(outputStream.toByteArray(),"UTF-8");       } catch (IOException e) {         e.printstacktrace();       }     }     return result;   }    public static inputStream getinputStream(String path) {     URL url;     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)         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();     }     return null;   }    public static byte[] readStream(inputStream inStream) throws Exception {     ByteArrayOutputStream outSteam = new ByteArrayOutputStream();     byte[] buffer = new byte[1024];     int len = -1;     while ((len = inStream.read(buffer)) != -1) {       outSteam.write(buffer,len);      }     outSteam.close();     inStream.close();     return outSteam.toByteArray();   }    public static voID copyStream(String url,file f) {     fileOutputStream fileOutputStream = null;     inputStream inputStream = null;     try {       inputStream = getinputStream(url);       byte[] data = new byte[1024];       int len = 0;       fileOutputStream = new fileOutputStream(f);       while ((len = inputStream.read(data)) != -1) {         fileOutputStream.write(data,len);       }     } catch (fileNotFoundException e) {       e.printstacktrace();     } catch (IOException e) {       e.printstacktrace();     } finally {       if (inputStream != null) {         try {           inputStream.close();         } catch (IOException e) {           e.printstacktrace();         }       }       if (fileOutputStream != null) {         try {           fileOutputStream.close();         } catch (IOException e) {           e.printstacktrace();         }       }     }   }  } 

MemoryCache.java

import java.lang.ref.softReference; import java.util.Collections; import java.util.HashMap; import java.util.Map; import androID.graphics.Bitmap;  public class MemoryCache {   private Map<String,SoftReference<Bitmap>> cache = Collections       .synchronizedMap(new HashMap<String,SoftReference<Bitmap>>());// 软引用    public Bitmap get(String ID) {     if (!cache.containsKey(ID))       return null;     SoftReference<Bitmap> ref = cache.get(ID);     return ref.get();   }    public voID put(String ID,Bitmap bitmap) {     cache.put(ID,new SoftReference<Bitmap>(bitmap));   }    public voID clear() {     cache.clear();   } } 

ImageLoader.java

import java.io.file; import java.io.fileinputStream; import java.io.fileNotFoundException; import java.io.UnsupportedEnCodingException; import java.net.URLEncoder; 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.BitmapFactory; import androID.graphics.drawable.BitmapDrawable; import androID.Widget.ImageVIEw;  public class ImageLoader {    private MemoryCache memoryCache = new MemoryCache();   private fileCache fileCache;   private Map<ImageVIEw,String> imageVIEws = Collections       .synchronizedMap(new WeakHashMap<ImageVIEw,String>());   private ExecutorService executorService;   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 = 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();     }     url = 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(stub_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       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) {     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 = new 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_tmp / 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),o2);     } catch (fileNotFoundException e) {     }     return null;   }    /**  * 任务队列  *   * @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,bmp);       if (imageVIEwReused(photoToload))         return;       Bitmapdisplayer bd = new Bitmapdisplayer(bmp,photoToload);       Activity a = (Activity) photoToload.imageVIEw.getContext();       a.runOnUiThread(bd);     }   }    boolean imageVIEwReused(PhotoToload photoToload) {     String tag = imageVIEws.get(photoToload.imageVIEw);     if (tag == null || !tag.equals(photoToload.url))       return true;     return false;   }    /**  * 显示位图在UI线程  *   * @author Scorpio.liu  *   */   class Bitmapdisplayer implements Runnable {     Bitmap bitmap;     PhotoToload photoToload;      public Bitmapdisplayer(Bitmap b,PhotoToload p) {       bitmap = b;       photoToload = p;     }      public voID run() {       if (imageVIEwReused(photoToload))         return;       if (bitmap != null) {         if (isSrc)           photoToload.imageVIEw.setimageBitmap(bitmap);         else           photoToload.imageVIEw.setBackgroundDrawable(new BitmapDrawable(bitmap));       } else {         if (isSrc)           photoToload.imageVIEw.setimageResource(stub_ID);         else           photoToload.imageVIEw.setBackgroundResource(stub_ID);       }     }   }    public voID clearCache() {     memoryCache.clear();     fileCache.clear();   }  } 

使用的时候用ImageLoader这个类就ok了，很方便~

希望本文所述对大家学习AndroID软件编程有所帮助。

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