##第一次装B，希望不喜勿喷... 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：

##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