java.io.FileNotFoundException：op

1.添加权限

//清单文件中添加
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

//Activity中调用获取权限方法
 private void checkNeedPermissions(){
        //6.0以上需要动态申请权限
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED
                || ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED
                || ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            //多个权限一起申请
            ActivityCompat.requestPermissions(this, new String[]{
                    Manifest.permission.CAMERA,
                    Manifest.permission.WRITE_EXTERNAL_STORAGE,
                    Manifest.permission.READ_EXTERNAL_STORAGE
            }, 1);
        }
    }

2.查看文件路径是否正确

//我的文件放在手机storage/sdcard0/110_001.txt
        File file = new File("/storage/emulated/0/110_001.txt");
        if(!file.exists()) {
            Log.e("MainActivity.this","File doesn't exist!");
            return;
        }
        try {

            FileInputStream is = new FileInputStream(file);
            byte[] b = new byte[is.available()];
            is.read(b);
            String result = new String(b);
            System.out.println("读取成功："+result);
        } catch (Exception e) {
            e.printStackTrace();
        }

3.判断sd卡是否存在及路径

  /**
     * 获取默认的文件路径
     *
     * @return
     */
    public static String getDefaultFilePath() {
        String filepath = "";
        File file = new File("/storage/emulated/0/110_001.txt");
        if (file.exists()) {
            filepath = file.getAbsolutePath();
        } else {
            filepath = "不适用";
        }
        return filepath;
    }
    /**
     * 获取SD卡根目录路径
     *
     * @return
     */
    public static String getSdCardPath() {
        boolean exist = isSdCardExist();
        String sdpath = "";
        if (exist) {
            sdpath = Environment.getExternalStorageDirectory()
                    .getAbsolutePath();
        } else {
            sdpath = "不适用";
        }
        return sdpath;

    }
    /**
     * 判断SDCard是否存在 [当没有外挂SD卡时，内置ROM也被识别为存在sd卡]
     *
     * @return
     */
    public static boolean isSdCardExist() {
        return Environment.getExternalStorageState().equals(
                Environment.MEDIA_MOUNTED);
    }

4.全部代码

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        checkNeedPermissions();
        isSdCardExist();

        getSdCardPath();

        String defaultFilePath = getDefaultFilePath();
        System.out.println(defaultFilePath+"1");
        File file = new File("/storage/emulated/0/110_001.txt");
//            File file =new File("/storage/emulated/0/110_001.txt");
        if(!file.exists()) {
            Log.e("MainActivity.this","File doesn't exist!");
            return;
        }
        try {

            FileInputStream is = new FileInputStream(file);
            System.out.println("192.168.31.110.001.txt");
            byte[] b = new byte[is.available()];
            is.read(b);
            String result = new String(b);
            System.out.println("读取成功："+result);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private void checkNeedPermissions(){
        //6.0以上需要动态申请权限
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED
                || ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED
                || ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            //多个权限一起申请
            ActivityCompat.requestPermissions(this, new String[]{
                    Manifest.permission.CAMERA,
                    Manifest.permission.WRITE_EXTERNAL_STORAGE,
                    Manifest.permission.READ_EXTERNAL_STORAGE
            }, 1);
        }
    }
    /**
     * 获取默认的文件路径
     *
     * @return
     */
    public static String getDefaultFilePath() {
        String filepath = "";
        File file = new File("/storage/emulated/0/110_001.txt");
        if (file.exists()) {
            filepath = file.getAbsolutePath();
        } else {
            filepath = "不适用";
        }
        return filepath;
    }
    /**
     * 获取SD卡根目录路径
     *
     * @return
     */
    public static String getSdCardPath() {
        boolean exist = isSdCardExist();
        String sdpath = "";
        if (exist) {
            sdpath = Environment.getExternalStorageDirectory()
                    .getAbsolutePath();
        } else {
            sdpath = "不适用";
        }
        return sdpath;

    }
    /**
     * 判断SDCard是否存在 [当没有外挂SD卡时，内置ROM也被识别为存在sd卡]
     *
     * @return
     */
    public static boolean isSdCardExist() {
        return Environment.getExternalStorageState().equals(
                Environment.MEDIA_MOUNTED);
    }
}