针对java.io.FileNotFoundException open failed: EACCES (Permission denied)出现的问题，是由于当前使用的安卓版本过高导致的，出现了文件访问失败。

1\解决方法是在AndroidMainfest中添加android:requestLegacyExternalStorage="true"

2\AndroidMainfest中添加

public void at_file()throws IOException {


    String sdcard=Environment.getDataDirectory().getPath().replace("data","sdcard");
    String test_p1=sdcard+test_p;

    //File file = new File(Environment.getExternalStorageDirectory(), "a.txt");
    File file=new File(sdcard,"a.txt");
    InputStream inputStream = new FileInputStream(file);

    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
    StringBuilder stringBuilder = new StringBuilder();
    String line;
    while ((line = reader.readLine()) != null) {
        stringBuilder.append(line);
    }
    String fileContent = stringBuilder.toString();
    System.out.println(fileContent);
}