三级缓存

工具类中的代码：

    //单例
    private static NetUtil instance;

    //图片内存缓存
    private LruCache<String, Bitmap> cache;
    //HashMap<String, Bitmap> m;//无序的
    //LinkedHashMap<String, Bitmap>m;//有序的
    private File saveDir;

    //私有构造方法
    private NetUtil(Context context) {
        int size = (int)(Runtime.getRuntime().freeMemory() * 0.3);
        cache = new LruCache<>(size);
        //图片文件缓存目录
        saveDir = new File(context.getCacheDir(), "img_cache");
        //不存在,创建
        if(!saveDir.exists()) {
            saveDir.mkdirs();
        }
    }

    //提供方法,获取对象
    public static NetUtil getInstance(Context context) {
        if(instance == null) {
            instance = new NetUtil(context);
        }
        return instance;
    }

    /*public interface ImageCallbak2 {
        void onStartLoadImage(String url, ImageView imageView);
        void onLoadImageSuccess(String url, Bitmap bitmap, ImageView imageView);
    }

    public void displayBitmap3(final String urlStr, final ImageView imageView) {
        displayBitmap(urlStr, imageView, new ImageCallbak2() {
            @Override
            public void onStartLoadImage(String url, ImageView imageView) {
                imageView.setTag(url);
            }

            @Override
            public void onLoadImageSuccess(String url, Bitmap bitmap, ImageView imageView) {
                if(imageView.getTag().equals(url)) {
                    imageView.setImageBitmap(bitmap);
                } else {
                    Log.i("TEST", "错乱");
                }
            }
        });
    }

    public void displayBitmap(final String url, final ImageView imageView, final ImageCallbak2 callbak2) {
        callbak2.onStartLoadImage(url, imageView);
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                callbak2.onLoadImageSuccess(url, bitmap, imageView);
            }
        };
    }*/

    //1 定义接口:合同
    public interface ImageCallback {
        void loadImageSuccess(String url, Bitmap bitmap);
    }

    //////////////////接口回调
    public void getBitmap(final String urlStr, final ImageCallback callback) {
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                callback.loadImageSuccess(urlStr, bitmap);
            }
        }.execute(urlStr);
    }

    //展示图片,没有错乱
    public void displayBitmap2(final String urlStr, final ImageView imageView) {
        //绑定url到imageview
        imageView.setTag(urlStr);
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                if(imageView.getTag().equals(urlStr)) {
                    imageView.setImageBitmap(bitmap);
                }else {
                    Log.i("TEST", "错乱");
                }
            }
        }.execute(urlStr);
    }

    //请求一张图片,展示给ImageView
    //异步任务
    public void displayBitmap(String urlStr, final ImageView imageView) {
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                imageView.setImageBitmap(bitmap);
            }
        }.execute(urlStr);
    }


    //获取图片
    public Bitmap getBitmap(String urlStr) {
        Bitmap result = null;
        //从内存中要
        result = cache.get(url2Key(urlStr));
        //内存命中
        if(result != null) {
            Log.i("TEST", "内存中加载图片: " + urlStr);
            return result;
        }

        //从磁盘中要
        result = getBitmapForFile(urlStr);
        //文件命中
        if(result != null) {
            Log.i("TEST", "磁盘中加载图片: " + urlStr);
            //先存到内存缓存
            cache.put(url2Key(urlStr), result);
            return result;
        }

        //从网络中请
        Log.i("TEST", "网络中加载图片: " + urlStr);
        result = getBitmapForNetwork(urlStr);
        //写文件
        saveBitmap2File(urlStr, result);
        //存到内存缓存
        cache.put(url2Key(urlStr), result);

        return result;
    }

    //将url转换成key
    //url 做key: 太长;如果作为文件名,不允许/ ?
    private String url2Key(String url) {
        //MD5 摘要方法
        //MessageDigest
        return String.valueOf(url.hashCode());
    }

    //将图片存到文件
    private void saveBitmap2File(String urlStr, Bitmap bitmap) {
        //格式: png jpeg(jpg)
        //质量: 0 100
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(new File(saveDir,url2Key(urlStr)));
            //图片质量压缩,   并输出到输出流
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }finally {
            if(fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    //从文件读取图片
    private Bitmap getBitmapForFile(String urlStr) {///////
        //解码文件为bitmap图片
        return BitmapFactory.decodeFile(new File(saveDir, url2Key(urlStr)).getAbsolutePath());
    }

    //执行一个网络请求,返回一个Bitmap
    //这一步做:请求图片
    private Bitmap getBitmapForNetwork(String urlStr) {
        Bitmap result = null;
        try {
            URL url = new URL(urlStr);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setConnectTimeout(5000);
            urlConnection.setReadTimeout(5000);
            int responseCode = urlConnection.getResponseCode();
            if(responseCode == 200) {
                result = BitmapFactory.decodeStream(urlConnection.getInputStream());
            }
        } catch (java.io.IOException e) {
            e.printStackTrace();
        }
        return result;
    }

    ///////////////////普通get请求

    public interface Callbak<T>{
        void onSuccess(T t);
    }

    ///执行一个网络请求,通过回调返回结果
    public void getRequest(final String urlStr, final Class clazz, final Callbak callbak) {
        new AsyncTask<String, Void, Object>(){
            @Override
            protected Object doInBackground(String... strings) {
                return getRequest(urlStr, clazz);
            }

            @Override
            protected void onPostExecute(Object o) {
                callbak.onSuccess(o);
            }
        }.execute(urlStr);
    }


    //执行一个网络请求,返回bean
    public <T> T getRequest(String urlStr, Class clazz) {
        return (T) new Gson().fromJson(getRequest(urlStr), clazz);
    }

    //执行一个网络请求,返回String结果
    public String getRequest(String urlStr) {
        String result = "";
        try {
            URL url = new URL(urlStr);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setConnectTimeout(5000);
            urlConnection.setReadTimeout(5000);
            int responseCode = urlConnection.getResponseCode();
            if(responseCode == 200) {
                result = stream2String(urlConnection.getInputStream());
            }
        } catch (java.io.IOException e) {
            e.printStackTrace();
        }
        return result;
    }

    private String stream2String(InputStream is) throws IOException {
        StringBuilder sb = new StringBuilder();

        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        for (String tmp = br.readLine(); tmp != null; tmp = br.readLine()) {
            sb.append(tmp);
        }

        return sb.toString();
    }