android 缓存使用简介

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网络图片在开发过程中，一般都将图片缓存到本地sd卡中（经常要使用的图片），方便下次直接引用而不再次请求网络耗费资源。而如果是自己开发搜索功能里有涉及到图片的显示，可以直接Map<String, SoftReference<Drawable>>，即软引用。软引用重要代码代码：package com.test.load; import java.lang.ref.SoftReference;import java.net.URL;import java.util.HashMap;import java.util.Map; import android.graphics.drawable.Drawable;import android.os.Handler;import android.os.Message; public class ThreadImgLoader {  private Map<String, SoftReference<Drawable>> imageCache=new HashMap<String, SoftReference<Drawable>>();     public Drawable loadDrawable(final String imgUrl, final ImageCallback callback){      if (imageCache.containsKey(imgUrl)) {        SoftReference<Drawable> sf=imageCache.get(imgUrl);        if (sf.get()!=null) {           return sf.get();        }      }      final Handler handler=new Handler(){        public void handleMessage(Message msg) {           callback.imageLoaded((Drawable) msg.obj);        }      };      new Thread(){        public void run() {           Drawable drawable=loadImgFromUrl(imgUrl);           if (drawable!=null) {              imageCache.put(imgUrl, new SoftReference<Drawable>(drawable));              Message msg=handler.obtainMessage(0, drawable);              handler.sendMessage(msg);           }        }      }.start();      return null;   }     public Drawable loadImgFromUrl(String imgUrl) {      try {        return Drawable.createFromStream(new URL(imgUrl).openStream(), "src");      } catch (Exception e) {        return null;      }   }     public interface ImageCallback{      public void imageLoaded(Drawable drawable);   }} 下面是缓存到SD卡的重要代码，当然你也可以搜索一下，这方面的东西很多。WeakHashMap也是使用了软引用，你可以去看它的源代码：package com.test; import java.io.File;import java.io.FileOutputStream;import java.io.OutputStream;import java.util.WeakHashMap; import android.graphics.Bitmap;import android.graphics.Bitmap.CompressFormat;import android.graphics.BitmapFactory;import android.os.Environment; public class MyImgCache extends WeakHashMap<String, Bitmap> {   private static MyImgCache myImgCache=new MyImgCache();   private static final String CACHE_FILE="/MyXiaoCaiImg";   public static MyImgCache getInstance(){      return myImgCache;   }     public boolean isBitmapExist(String url) {      boolean isexist=false;      String name=changeUrlName(url);      String filePath=isMakeFile();      File file=new File(filePath, name);      if (containsKey(url)) {        isexist=true;      }else if (file.exists()) {        String path=file.getAbsolutePath();        System.out.println(path);        Bitmap bitmap=BitmapFactory.decodeFile(path);        if (bitmap!=null) {           put(url, bitmap, false);           isexist=true;        }      }      return isexist;   }    private String changeUrlName(String url) {      String name = url.replaceAll(":", "_");      name = name.replaceAll("//", "_");      name = name.replaceAll("/", "_");      name = name.replaceAll("=", "_");      name = name.replaceAll(",", "_");      name = name.replaceAll("&", "_");      return name;   }     private String isMakeFile() {      String rootpath = null;      if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {        rootpath = Environment.getExternalStorageDirectory().toString();      }      String filepath = rootpath + CACHE_FILE;      File file = new File(filepath);      if (!file.exists()) {        file.mkdirs();      }      return filepath;   }    public Bitmap put(String key, Bitmap value) {      String name=changeUrlName(key);      String filePath=isMakeFile();      File file = new File(filePath, name);      OutputStream outputStream = null;      try {        outputStream = new FileOutputStream(file);        value.compress(CompressFormat.JPEG, 100, outputStream);        outputStream.flush();        outputStream.close();        outputStream = null;      } catch (Exception e) {        e.printStackTrace();      }      return super.put(key, value);   }    public Bitmap put(String key, Bitmap value, boolean b) {      if (b) {        return this.put(key, value);      }else {        return super.put(key, value);      }   } }