这里说的三级缓存,分别指的是:内存缓存、文件缓存和网络这三个层面。
一般来说,我们首次加载图片,内存和文件是没有缓存的,这样我们需要从网络加载,加载完成后,我们会存到内存和文件中去;当再次加载图片的时候,我们会先查找内存有没有,如果有就直接显示内存中的图片,如果没有,我们会接着查找文件中是否有,如果文件中有,我们会显示文件中的图片,并且把它存到内存中去,这样下次我们在内存中就能找到它了。
我们之所以要做缓存,主要是为了提高效率,节省流量。但是为什么要做三级呢?为什么不只存在内存或者只存在文件中呢?这是因为内存的读取速度快,但是容易被回收,容量小,文件的读取速度次之,不过容量大,不到不得已不会被回收。
//权限
<uses-permission android:name="android.permission.INTERNET"></uses-permission><uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"></uses-permission><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
/** * author:Created by WangZhiQiang on 2017-09-04. * 处理三级缓存 * 内存缓存(LruCache-->最近最少使用算法,当缓存慢的时候,自动把最近使用最少的删除,腾出来的空间添加新的缓存内容) * sd卡缓存 * 网络 */
-
- public class ImagesUtils {
- Handler handler;
- private final File cacheDir;
- private final ExecutorService newFixedThreadPool;
- private final LruCache<String, Bitmap> lruCache;
-
- public ImagesUtils (Context context, Handler handler){
- this.handler = handler;
-
- long maxMemory = Runtime.getRuntime().maxMemory();
- int maxSize = (int) (maxMemory / 8);
-
- cacheDir = context.getCacheDir();
-
- newFixedThreadPool = Executors.newFixedThreadPool(5);
- lruCache = new LruCache<String, Bitmap>(maxSize) {
-
- @Override
- protected int sizeOf(String key, Bitmap value) {
- return value.getRowBytes()*value.getHeight();
- }
- };
- }
-
-
-
-
-
-
- public Bitmap getBitMap(String path){
-
- Bitmap bitmap = lruCache.get(path);
- if(bitmap!=){
- System.out.println("我走了内存");
- return bitmap;
- }
-
- bitmap = getBitMapFromLocal(path);
- if(bitmap!=){
- System.out.println("我走了本地缓存");
- return bitmap;
- }
-
- getBitmapFromNet(path);
-
- return ;
- }
-
-
-
-
-
- private void getBitmapFromNet(final String path) {
-
- newFixedThreadPool.execute(new Runnable() {
- @Override
- public void run() {
- try {
- URL url=new URL(path);
- HttpURLConnection connection = (HttpURLConnection) url.openConnection();
- connection.setConnectTimeout(5000);
- connection.setReadTimeout(5000);
- int code = connection.getResponseCode();
- if(code==200){
- InputStream inputStream = connection.getInputStream();
- Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
- Message msg = new Message();
- msg.what = 111;
- msg.obj = bitmap;
- Bundle data = new Bundle();
- data.putString("tag", path);
- msg.setData(data);
- handler.sendMessage(msg);
-
- saveBitmapToLocal(bitmap, path);
-
- lruCache.put(path, bitmap);
- }
- } catch (Exception e) {
- e.printStackTrace();
- }
- }
-
- });
- }
- protected void saveBitmapToLocal(Bitmap bitmap, String path) {
- try {
- String encode = EncoderUtils.encode(path);
- FileOutputStream fileOutputStream = new FileOutputStream(cacheDir + "/" + encode);
-
- bitmap.compress(Bitmap.CompressFormat.JPEG, 80, fileOutputStream);
- } catch (Exception e) {
- e.printStackTrace();
- }
-
- }
- private Bitmap getBitMapFromLocal(String path) {
- try {
- String encode = EncoderUtils.encode(path);
- FileInputStream fileInputStream = new FileInputStream(cacheDir
- + "/" + encode);
- Bitmap bitmap = BitmapFactory.decodeStream(fileInputStream);
-
- lruCache.put(path, bitmap);
- return bitmap;
- } catch (Exception e) {
- e.printStackTrace();
- }
- return ;
- }
- }
-
-
-
-
-
-
- public class EncoderUtils {
-
-
-
-
-
-
-
- public static String encode(String string) throws Exception {
- byte[] hash = MessageDigest.getInstance("MD5").digest(
- string.getBytes("UTF-8"));
- StringBuilder hex = new StringBuilder(hash.length * 2);
- for (byte b : hash) {
- if ((b & 0xFF) < 0x10) {
- hex.append("0");
- }
- hex.append(Integer.toHexString(b & 0xFF));
- }
- return hex.toString();
- }
-
-
- }
- public class MainActivity extends AppCompatActivity {
-
- private GridView gv;
- String[] imageUrls = new String[] {
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uplds/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383291_6518.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383291_8239.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383290_9329.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383290_1042.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383275_3977.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383265_8550.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383264_3954.jpg",
- "http://img.my.csdn.net/uploads/201407/26/1406383264_4787.jpg",
- };
-
- Handler handler=new Handler(){
- @Override
- public void handleMessage(Message msg) {
- super.handleMessage(msg);
- }
- };
- private ImagesUtils imagesutils;
-
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- imagesutils = new ImagesUtils(this,handler);
- gv = (GridView) findViewById(R.id.gv);
- gv.setAdapter(new myadaper());
- }
- class myadaper extends BaseAdapter{
-
- @Override
- public int getCount() {
- return imageUrls.length;
- }
-
- @Override
- public Object getItem(int i) {
- return ;
- }
-
- @Override
- public long getItemId(int i) {
- return 0;
- }
-
- @Override
- public View getView(int i, View view, ViewGroup viewGroup) {
- ImageView iv = new ImageView(MainActivity.this);
- iv.setTag(imageUrls[i]);
-
- Bitmap bitmap = imagesutils.getBitMap(imageUrls[i]);
-
- if(bitmap !=){
- iv.setImageBitmap(bitmap);
- }
-
- return iv;
- }
- }
- }