1.内存缓存

package com.ljlt.utils;import java.util.Collections;import java.util.Iterator;import java.util.LinkedHashMap;import java.util.Map;import java.util.Map.Entry;import android.graphics.Bitmap;import android.util.Log;public class MemoryCache {	private static final String TAG = "MemoryCache";	// 放入缓存时是个同步操作	// LinkedHashMap构造方法的最后一个参数true代表这个map里的元素将按照最近使用次数由少到多排列，即LRU	// 这样的好处是如果要将缓存中的元素替换，则先遍历出最近最少使用的元素来替换以提高效率	private Map
    
      cache = Collections			.synchronizedMap(new LinkedHashMap
     
      (10, 1.5f, true));	// 缓存中图片所占用的字节，初始0，将通过此变量严格控制缓存所占用的堆内存	private long size = 0;// current allocated size	// 缓存只能占用的最大堆内存	private long limit = 1000000;// max memory in bytes	public MemoryCache() {		// use 25% of available heap size		setLimit(Runtime.getRuntime().maxMemory() / 4);	}	public void setLimit(long new_limit) { 		limit = new_limit;		Log.i(TAG, "MemoryCache will use up to " + limit / 1024. / 1024. + "MB");	}	public Bitmap get(String id) {		try {			if (!cache.containsKey(id))				return null;			return cache.get(id);		} catch (NullPointerException ex) {			return null;		}	}	public void put(String id, Bitmap bitmap) {		try {			if (cache.containsKey(id))				size -= getSizeInBytes(cache.get(id));			cache.put(id, bitmap);			size += getSizeInBytes(bitmap);			checkSize();		} catch (Throwable th) {			th.printStackTrace();		}	}	/**	 * 严格控制堆内存，如果超过将首先替换最近最少使用的那个图片缓存	 * 	 */	private void checkSize() {		Log.i(TAG, "cache size=" + size + " length=" + cache.size());		if (size > limit) {			// 先遍历最近最少使用的元素			Iterator
      
       
        > iter = cache.entrySet().iterator();			while (iter.hasNext()) {				Entry
        
          entry = iter.next();				size -= getSizeInBytes(entry.getValue());				iter.remove();				if (size <= limit)					break;			}			Log.i(TAG, "Clean cache. New size " + cache.size());		}	}	public void clear() {		cache.clear();	}	/**	 * 图片占用的内存	 * 	 * @param bitmap	 * @return	 */	long getSizeInBytes(Bitmap bitmap) {		if (bitmap == null)			return 0;		return bitmap.getRowBytes() * bitmap.getHeight();	}}
        
       
      
     
    

2.文件缓存

package com.ljlt.utils;import java.io.File;import android.content.Context;public class FileCache {	private File cacheDir;	public FileCache(Context context) {		// 如果有SD卡则在SD卡中建一个LazyList的目录存放缓存的图片		// 没有SD卡就放在系统的缓存目录中		if (android.os.Environment.getExternalStorageState().equals(				android.os.Environment.MEDIA_MOUNTED))			cacheDir = new File(					android.os.Environment.getExternalStorageDirectory(),					"LazyList");		else			cacheDir = context.getCacheDir();		if (!cacheDir.exists())			cacheDir.mkdirs();	}	public File getFile(String url) {		// 将url的hashCode作为缓存的文件名		String filename = String.valueOf(url.hashCode());		// Another possible solution		// String filename = URLEncoder.encode(url);		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();	}}

3.最主要的类

package com.ljlt.utils;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.InputStream;import java.io.OutputStream;import java.net.HttpURLConnection;import java.net.URL;import java.util.Collections;import java.util.Map;import java.util.WeakHashMap;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import com.ljlt.activity.R;import android.app.Activity;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.widget.ImageView;public class ImageLoader2 {	MemoryCache memoryCache = new MemoryCache();	FileCache fileCache;	private Map
    
      imageViews = Collections			.synchronizedMap(new WeakHashMap
     
      ());	// 线程池	ExecutorService executorService;	public ImageLoader2(Context context) {		fileCache = new FileCache(context);		executorService = Executors.newFixedThreadPool(5);	}	// 当进入listview时默认的图片，可换成你自己的默认图片	final int stub_id = R.drawable.default_pic;	// 最主要的方法	public void DisplayImage(String url, ImageView imageView) {		imageViews.put(imageView, url);		// 先从内存缓存中查找		Bitmap bitmap = memoryCache.get(url);		if (bitmap != null)			imageView.setImageBitmap(bitmap);		else {			// 若没有的话则开启新线程加载图片			queuePhoto(url, imageView);			imageView.setImageResource(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) {		File f = fileCache.getFile(url);		// 先从文件缓存中查找是否有		Bitmap b = decodeFile(f);		if (b != null)			return b;		// 最后从指定的url中下载图片		try {			Bitmap bitmap = null;			URL imageUrl = new URL(url);			HttpURLConnection conn = (HttpURLConnection) imageUrl					.openConnection();			conn.setConnectTimeout(30000);			conn.setReadTimeout(30000);			conn.setInstanceFollowRedirects(true);			InputStream is = conn.getInputStream();			OutputStream os = new FileOutputStream(f);			CopyStream(is, os);			os.close();			bitmap = decodeFile(f);			return bitmap;		} catch (Exception ex) {			ex.printStackTrace();			return null;		}	}	// decode这个图片并且按比例缩放以减少内存消耗，虚拟机对每张图片的缓存大小也是有限制的	private Bitmap decodeFile(File f) {		try {			// decode image size			BitmapFactory.Options o = new BitmapFactory.Options();			o.inJustDecodeBounds = true;			BitmapFactory.decodeStream(new FileInputStream(f), null, o);			// Find the correct scale value. It should be the power of 2.			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;			}			// decode with inSampleSize			BitmapFactory.Options o2 = new BitmapFactory.Options();			o2.inSampleSize = scale;			return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);		} catch (FileNotFoundException e) {		}		return null;	}	// Task for the queue	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);			// 更新的操作放在UI线程中			Activity a = (Activity) photoToLoad.imageView.getContext();			a.runOnUiThread(bd);		}	}	/**	 * 防止图片错位	 * 	 * @param photoToLoad	 * @return	 */	boolean imageViewReused(PhotoToLoad photoToLoad) {		String tag = imageViews.get(photoToLoad.imageView);		if (tag == null || !tag.equals(photoToLoad.url))			return true;		return false;	}	// 用于在UI线程中更新界面	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)				photoToLoad.imageView.setImageBitmap(bitmap);			else				photoToLoad.imageView.setImageResource(stub_id);		}	}	public void clearCache() {		memoryCache.clear();		fileCache.clear();	}	public static void CopyStream(InputStream is, OutputStream os) {		final int buffer_size = 1024;		try {			byte[] bytes = new byte[buffer_size];			for (;;) {				int count = is.read(bytes, 0, buffer_size);				if (count == -1)					break;				os.write(bytes, 0, count);			}		} catch (Exception ex) {		}	}}
     
    

4.使用

 imageLoader=new ImageLoader2(context);

imageLoader.DisplayImage(url, viewHolder.image);

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