imagedownload.md

图片下载原理

1. 使用OKHttpClient或HttpConnection 发送一个网络请求，返回一个inputStream 转化为byte数组， 通过BitmapFactory 将byte数组转化成bitmap，此时可以直接使用，也可以存储到本地

    /**
     * Get data from stream
     * @param inStream
     * @return byte[]
     * @throws Exception
     */
    public static byte[] readStream(InputStream inStream) throws Exception{
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while( (len=inStream.read(buffer)) != -1){
            outStream.write(buffer, 0, len);
        }
        outStream.close();
        inStream.close();
        return outStream.toByteArray();
    }
   

// 使用OKHttp就可以通过response.body获取

  private void asyncGet() {
        client = new OkHttpClient();
        final Request request = new Request.Builder().get()
                .url(IMAGE_URL)
                .build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {

                Message message = handler.obtainMessage();
                if (response.isSuccessful()) {
                    message.what = IS_SUCCESS;
                    message.obj = response.body().bytes();
                    handler.sendMessage(message);
                } else {
                    handler.sendEmptyMessage(IS_FAIL);
                }
            }
        });
    }