先附上我的源码Github地址
https://github.com/xiaweizi/ImageCache.git
图片的缓存虽然现在已经有不少的框架，但是我还是想自己学习一下图片的缓存机制。图片缓存的大概逻辑就是：当需要获取图片的时候，首先判断内存是否有，有---加载，无---从本地中获取图片，有--加载，无--从网络中下载，然后缓存到内存和本地中。大概流程图如下：
图片的三级缓存.png
首先从易到难
1. 内存缓存
１. 新建LruCache对象
private LruCache<String, Bitmap> mMemoryCache;
2. 在构造函数中初始化LruCache
final long maxMemory = Runtime.getRuntime().maxMemory() / 8;
mMemoryCache = new LruCache<String, Bitmap>((int) maxMemory){
@Override
protected int sizeOf (String key, Bitmap value) {
int byteCount = value.getByteCount();
Log.i(TAG, "每个Bitmap大小：" + byteCount + "每个程序最大内存" + maxMemory);
return byteCount;
}
};
3. 利用键值对的方式存到内存中
public void setBitmapToMemory(Bitmap bitmap, String url){
Log.i(TAG, "图片已经保存到内存中: ");
mMemoryCache.put(url, bitmap);
}
4. 从内存中取出图片
public Bitmap getBitmapFromMemory(String url){
return mMemoryCache.get(url);
}
2.本地缓存
1. 创建要缓存的路径
private static final String CACHE_PATH = Environment.getExternalStorageDirectory().getAbsolutePath();
2. 利用输入流进行文件的本地存储，其中对文件名进行了MD5加密
try {
Log.i(TAG, "cachePath: " + CACHE_PATH);
String filename = MD5Encoder.encode(url);
File file = new File(CACHE_PATH, filename);
File parentFile = file.getParentFile();
if (!parentFile.exists()){
parentFile.mkdirs();
}
Log.i(TAG, "图片存到本地中: ");
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, new FileOutputStream(file));
} catch (FileNotFoundException e) {
e.printStackTrace();
Log.i(TAG, "setBitmapToLocal: " + e);
}
3. 利用输出流进行文件的读取
try {
String fileName = MD5Encoder.encode(url);
File file = new File(CACHE_PATH, fileName);
Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(file));
Log.i(TAG, "从本地获取图片: ");
return bitmap;
} catch (FileNotFoundException e) {
e.printStackTrace();
}
return null;
3.从网络中获取图片
1. 利用构造函数获取LocalCacheUtil和MemoryCacheUtil对象
public NetCache (LocalCache mLocache, MemoryCache mMemoryCache) {
this.mLocache = mLocache;
this.mMemoryCache = mMemoryCache;
}
2. 新建私有类，从url中获取图片
HttpURLConnection conn = null;
try {
conn = (HttpURLConnection) new URL(url).openConnection();
conn.setConnectTimeout(4000);
conn.setReadTimeout(4000);
conn.setRequestMethod("GET");
int responseCode = conn.getResponseCode();
if (responseCode == 200){
//图片压缩
BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 2;//宽高压缩为原来的1/2
options.inPreferredConfig = Bitmap.Config.ARGB_4444;
Bitmap bitmap = BitmapFactory.decodeStream(conn.getInputStream(), null, options);
return bitmap;
}
} catch (IOException e) {
e.printStackTrace();
Log.i(TAG, "downLoadBitmap: " + e);
}finally {
conn.disconnect();
}
return null;
}
3. 利用AsyncTask的方式异步加载数据
class BitmapTask extends AsyncTask<Object, Integer, Bitmap>{
@Override
protected void onPreExecute () {
Log.i(TAG, "onPreExecute: ");
super.onPreExecute();
}
@Override
protected void onProgressUpdate (Integer... values) {
Log.i(TAG, "onProgressUpdate: ");
super.onProgressUpdate(values);
}
@Override
protected Bitmap doInBackground (Object... params) {
Log.i(TAG, "doInBackground: ");
iv = (ImageView) params[0];
url = (String) params[1];
Bitmap bitmap = downLoadBitmap(url);
return bitmap;
}
@Override
protected void onPostExecute (Bitmap bitmap) {
Log.i(TAG, "onPostExecute: ");
if (bitmap != null){
Log.i(TAG, "已经从网络中获取到图片: ");
iv.setImageBitmap(bitmap);
Log.i(TAG, "url: " + url + "Bitmap" + bitmap.getByteCount());
mMemoryCache.setBitmapToMemory(bitmap, url);
mLocache.setBitmapToLocal(bitmap, url);
}
}
4.最后创建一个util进行逻辑的封装，即一开始的流程图
public class MyBitmapUtil {
private static final String TAG = "MyBitmapUtil----->";
private LocalCache mLocal;
private MemoryCache mMemory;
private NetCache mNet;
public MyBitmapUtil () {
mLocal = new LocalCache();
mMemory = new MemoryCache();
mNet = new NetCache(mLocal, mMemory);
}
public void disPlay(ImageView iv, String url){
iv.setImageResource(R.mipmap.ic_launcher);
Bitmap bitmap = null;
bitmap = mMemory.getBitmapFromMemory(url);
if (bitmap != null){
iv.setImageBitmap(bitmap);
return;
}
bitmap = mLocal.getBitmapFromLocal(url);
if (bitmap != null){
iv.setImageBitmap(bitmap);
mMemory.setBitmapToMemory(bitmap, url);
return;
}
mNet.getBitmapFromNet(iv, url);
}
}
最后附上我的源码Github地址
https://github.com/xiaweizi/ImageCache.git
