Textdatei auf SD Karte auslesen funktioniert nicht (Oneplus One)

package com.example.rling.stark_inspektion;

import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import android.widget.Button;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Scanner;

public class MainActivity extends AppCompatActivity {
    private Button importButton;
    private TextView filetext;


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

        importButton = (Button) findViewById(R.id.import_button);
        filetext = (TextView) findViewById(R.id.textView);

        importButton.setText(R.string.import_button);

        importButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                File sdcard = Environment.getExternalStorageDirectory();
                File file =  new File(sdcard, "/Download/testfile.txt");  

                if(file.exists()) {
                    //filetext.setText("File exists\n"); 
                    StringBuilder text = new StringBuilder();
                    try {
                        BufferedReader br = new BufferedReader(new FileReader(file));
                        String line;

                        while((line = br.readLine()) != null) {
                            text.append(line);
                            text.append("\n");  
                            System.out.println(line);
                        }
                    }catch (Exception e) {

                    }
                    System.out.println(text);
                    filetext.setText(text);
                } else {
                    filetext.setText("File not found.");  
                }
            }
        });

    }
}

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"></uses-permission>