Android调用系统自带的文件管理器进行文件选择并读取

先调用：

intent = new Intent(Intent.ACTION_GET_CONTENT);
intent.setType("*/*");　　　　　　　　　　　　　　　　//设置类型，我这里是任意类型，任意后缀的可以这样写。
intent.addCategory(Intent.CATEGORY_OPENABLE);　　 // 只有设置了这个，返回的uri才能使用 getContentResolver().openInputStream(uri) 打开。
startActivityForResult(intent, 1);

再在 onActivityResult 里做对uri相应的操作（目前只能读操作）

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if(resultCode == Activity.RESULT_OK && data != null) {
            try {
                readBytes(data.getData());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
    public byte[] readBytes(Uri inUri) throws IOException {
        InputStream inputStream = getContentResolver().openInputStream(inUri);
        
        // this dynamically extends to take the bytes you read
        ByteArrayOutputStream byteBuffer = new ByteArrayOutputStream();

        // this is storage overwritten on each iteration with bytes
        int bufferSize = 1024;
        byte[] buffer = new byte[bufferSize];

        // we need to know how may bytes were read to write them to the byteBuffer
        int len = 0;
        while ((len = inputStream.read(buffer)) != -1) {
          byteBuffer.write(buffer, 0, len);
          Log.i("welhzh_f", "" + len);
        }

        // and then we can return your byte array.
        return byteBuffer.toByteArray();
      }