android下载网络图片并缓存
异步下载网络图片,并提供是否缓存至内存或外部文件的功能
异步加载类AsyncImageLoader
public void downloadImage(final String url, final ImageCallback callback);
public void downloadImage(final String url, final boolean cache2Memory, final ImageCallback callback);
public void setCache2File(boolean flag);
public void setCachedDir(String dir);
图片下载和缓存实现类LoaderImpl
1.AsyncImageLoader.java
- package com.imagecache;
- import java.lang.ref.SoftReference;
- import java.util.HashMap;
- import java.util.HashSet;
- import java.util.Map;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- import android.content.Context;
- import android.graphics.Bitmap;
- import android.os.Handler;
- import android.util.Log;
- public class AsyncImageLoader {
- //保存正在下载的图片URL集合,避免重复下载用
- private static HashSet<String> sDownloadingSet;
- //软引用内存缓存
- private static Map<String,SoftReference<Bitmap>> sImageCache;
- //图片三种获取方式管理者,网络URL获取、内存缓存获取、外部文件缓存获取
- private static LoaderImpl impl;
- //线程池相关
- private static ExecutorService sExecutorService;
- //通知UI线程图片获取ok时使用
- private Handler handler;
- /**
- * 异步加载图片完毕的回调接口
- */
- public interface ImageCallback{
- /**
- * 回调函数
- * @param bitmap: may be null!
- * @param imageUrl
- */
- public void onImageLoaded(Bitmap bitmap, String imageUrl);
- }
- static{
- sDownloadingSet = new HashSet<String>();
- sImageCache = new HashMap<String,SoftReference<Bitmap>>();
- impl = new LoaderImpl(sImageCache);
- }
- public AsyncImageLoader(Context context){
- handler = new Handler();
- startThreadPoolIfNecessary();
- String defaultDir = context.getCacheDir().getAbsolutePath();
- setCachedDir(defaultDir);
- }
- /**
- * 是否缓存图片至/data/data/package/cache/目录
- * 默认不缓存
- */
- public void setCache2File(boolean flag){
- impl.setCache2File(flag);
- }
- /**
- * 设置缓存路径,setCache2File(true)时有效
- */
- public void setCachedDir(String dir){
- impl.setCachedDir(dir);
- }
- /**开启线程池*/
- public static void startThreadPoolIfNecessary(){
- if(sExecutorService == null || sExecutorService.isShutdown() || sExecutorService.isTerminated()){
- sExecutorService = Executors.newFixedThreadPool(3);
- //sExecutorService = Executors.newSingleThreadExecutor();
- }
- }
- /**
- * 异步下载图片,并缓存到memory中
- * @param url
- * @param callback see ImageCallback interface
- */
- public void downloadImage(final String url, final ImageCallback callback){
- downloadImage(url, true, callback);
- }
- /**
- *
- * @param url
- * @param cache2Memory 是否缓存至memory中
- * @param callback
- */
- public void downloadImage(final String url, final boolean cache2Memory, final ImageCallback callback){
- if(sDownloadingSet.contains(url)){
- Log.i("AsyncImageLoader", "###该图片正在下载,不能重复下载!");
- return;
- }
- Bitmap bitmap = impl.getBitmapFromMemory(url);
- if(bitmap != null){
- if(callback != null){
- callback.onImageLoaded(bitmap, url);
- }
- }else{
- //从网络端下载图片
- sDownloadingSet.add(url);
- sExecutorService.submit(new Runnable(){
- @Override
- public void run() {
- final Bitmap bitmap = impl.getBitmapFromUrl(url, cache2Memory);
- handler.post(new Runnable(){
- @Override
- public void run(){
- if(callback != null)
- callback.onImageLoaded(bitmap, url);
- sDownloadingSet.remove(url);
- }
- });
- }
- });
- }
- }
- /**
- * 预加载下一张图片,缓存至memory中
- * @param url
- */
- public void preLoadNextImage(final String url){
- //将callback置为空,只将bitmap缓存到memory即可。
- downloadImage(url, null);
- }
- }
2.LoaderImpl.java
- package com.imagecache;
- import java.io.FileInputStream;
- import java.io.FileNotFoundException;
- import java.io.FileOutputStream;
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.UnsupportedEncodingException;
- import java.lang.ref.SoftReference;
- import java.net.HttpURLConnection;
- import java.net.URL;
- import java.security.MessageDigest;
- import java.security.NoSuchAlgorithmException;
- import java.util.Map;
- import android.graphics.Bitmap;
- import android.graphics.BitmapFactory;
- /**
- *
- * @author Administrator
- * @desc 异步加载图片管理器
- *
- */
- public class LoaderImpl {
- //内存中的软应用缓存
- private Map<String, SoftReference<Bitmap>> imageCache;
- //是否缓存图片至本地文件
- private boolean cache2FileFlag = false;
- //缓存目录,默认是/data/data/package/cache/目录
- private String cachedDir;
- public LoaderImpl(Map<String, SoftReference<Bitmap>> imageCache){
- this.imageCache = imageCache;
- }
- /**
- * 是否缓存图片至外部文件
- * @param flag
- */
- public void setCache2File(boolean flag){
- cache2FileFlag = flag;
- }
- /**
- * 设置缓存图片到外部文件的路径
- * @param cacheDir
- */
- public void setCachedDir(String cacheDir){
- this.cachedDir = cacheDir;
- }
- /**
- * 从网络端下载图片
- * @param url 网络图片的URL地址
- * @param cache2Memory 是否缓存(缓存在内存中)
- * @return bitmap 图片bitmap结构
- *
- */
- public Bitmap getBitmapFromUrl(String url, boolean cache2Memory){
- Bitmap bitmap = null;
- try{
- URL u = new URL(url);
- HttpURLConnection conn = (HttpURLConnection)u.openConnection();
- InputStream is = conn.getInputStream();
- bitmap = BitmapFactory.decodeStream(is);
- if(cache2Memory){
- //1.缓存bitmap至内存软引用中
- imageCache.put(url, new SoftReference<Bitmap>(bitmap));
- if(cache2FileFlag){
- //2.缓存bitmap至/data/data/packageName/cache/文件夹中
- String fileName = getMD5Str(url);
- String filePath = this.cachedDir + "/" +fileName;
- FileOutputStream fos = new FileOutputStream(filePath);
- bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
- }
- }
- is.close();
- conn.disconnect();
- return bitmap;
- }catch(IOException e){
- e.printStackTrace();
- return null;
- }
- }
- /**
- * 从内存缓存中获取bitmap
- * @param url
- * @return bitmap or null.
- */
- public Bitmap getBitmapFromMemory(String url){
- Bitmap bitmap = null;
- if(imageCache.containsKey(url)){
- synchronized(imageCache){
- SoftReference<Bitmap> bitmapRef = imageCache.get(url);
- if(bitmapRef != null){
- bitmap = bitmapRef.get();
- return bitmap;
- }
- }
- }
- //从外部缓存文件读取
- if(cache2FileFlag){
- bitmap = getBitmapFromFile(url);
- if(bitmap != null)
- imageCache.put(url, new SoftReference<Bitmap>(bitmap));
- }
- return bitmap;
- }
- /**
- * 从外部文件缓存中获取bitmap
- * @param url
- * @return
- */
- private Bitmap getBitmapFromFile(String url){
- Bitmap bitmap = null;
- String fileName = getMD5Str(url);
- if(fileName == null)
- return null;
- String filePath = cachedDir + "/" + fileName;
- try {
- FileInputStream fis = new FileInputStream(filePath);
- bitmap = BitmapFactory.decodeStream(fis);
- } catch (FileNotFoundException e) {
- e.printStackTrace();
- bitmap = null;
- }
- return bitmap;
- }
- /**
- * MD5 加密
- */
- private static String getMD5Str(String str) {
- MessageDigest messageDigest = null;
- try {
- messageDigest = MessageDigest.getInstance("MD5");
- messageDigest.reset();
- messageDigest.update(str.getBytes("UTF-8"));
- } catch (NoSuchAlgorithmException e) {
- System.out.println("NoSuchAlgorithmException caught!");
- return null;
- } catch (UnsupportedEncodingException e) {
- e.printStackTrace();
- return null;
- }
- byte[] byteArray = messageDigest.digest();
- StringBuffer md5StrBuff = new StringBuffer();
- for (int i = 0; i < byteArray.length; i++) {
- if (Integer.toHexString(0xFF & byteArray[i]).length() == 1)
- md5StrBuff.append("0").append(Integer.toHexString(0xFF & byteArray[i]));
- else
- md5StrBuff.append(Integer.toHexString(0xFF & byteArray[i]));
- }
- return md5StrBuff.toString();
- }
- /**
- * MD5 加密
- private static String getMD5Str(Object...objects){
- StringBuilder stringBuilder=new StringBuilder();
- for (Object object : objects) {
- stringBuilder.append(object.toString());
- }
- return getMD5Str(stringBuilder.toString());
- }*/
- }
3.测试Activity
- package com.imagecache;
- import android.app.Activity;
- import android.graphics.Bitmap;
- import android.os.Bundle;
- import android.widget.ImageView;
- public class MainActivity extends Activity {
- /** Called when the activity is first created. */
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- final ImageView iv = (ImageView)findViewById(R.id.iv);
- //网络图片地址
- String imgUrl = "http://...";
- //for test
- AsyncImageLoader loader = new AsyncImageLoader(getApplicationContext());
- //将图片缓存至外部文件中
- loader.setCache2File(true); //false
- //设置外部缓存文件夹
- loader.setCachedDir(this.getCacheDir().getAbsolutePath());
- //下载图片,第二个参数是否缓存至内存中
- loader.downloadImage(imgUrl, true/*false*/, new AsyncImageLoader.ImageCallback() {
- @Override
- public void onImageLoaded(Bitmap bitmap, String imageUrl) {
- if(bitmap != null){
- iv.setImageBitmap(bitmap);
- }else{
- //下载失败,设置默认图片
- }
- }
- });
- }
- }