File.createNewFile() method throws exception in Android M

问题

I have a problem to create file in Android M.

I use Nexus 9 with Android 6.0.1. Then I set in my project as below:

AndroidManifest.xml

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

build.gradle

android {
    defaultConfig {
        targetSdkVersion 23
        ...
    }
}

MainActivity.Java

public class MainActivity extends AppCompatActivity {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    String storagePath = Environment.getExternalStorageDirectory().getAbsolutePath();
    String rootPath = storagePath + "/test";
    String fileName = "/test.zip";

    File root = new File(rootPath);
    if(!root.mkdirs()) {
        Log.i("Test", "This path is already exist: " + root.getAbsolutePath());
    }

    File file = new File(rootPath + fileName);
    try {
        if (!file.createNewFile()) {
            Log.i("Test", "This file is already exist: " + file.getAbsolutePath());
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
}

Build was success and application was launched, but I got exception message like this:

IOExceiption

01-07 18:13:40.669 18027-18027/com.sample.myapplication W/System.err: java.io.IOException: open failed: ENOENT (No such file or directory)
01-07 18:13:40.669 18027-18027/com.sample.myapplication W/System.err:     at java.io.File.createNewFile(File.java:939)
01-07 18:13:40.669 18027-18027/com.sample.myapplication W/System.err:     at com.sample.myapplication.MainActivity.onCreate(MainActivity.java:36)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.Activity.performCreate(Activity.java:6251)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.-wrap11(ActivityThread.java)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.os.Looper.loop(Looper.java:148)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5417)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err: Caused by: android.system.ErrnoException: open failed: ENOENT (No such file or directory)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at libcore.io.Posix.open(Native Method)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at libcore.io.BlockGuardOs.open(BlockGuardOs.java:186)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at java.io.File.createNewFile(File.java:932)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:   ... 13 more

How can I solve this problem? I don't catch what I miss....

Please help.

回答1:

I edit my code: Add "request to checks permission" code at onCreate.

Thanks, laalto.

I didn't know about runtime permission.

I solved exception like this:

MainActivity.java

public class MainActivity extends AppCompatActivity {

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

        /* Request user permissions in runtime */
        ActivityCompat.requestPermissions(MainActivity.this,
            new String[] {
                    Manifest.permission.READ_EXTERNAL_STORAGE,
                    Manifest.permission.WRITE_EXTERNAL_STORAGE
            },
            100);
        /* Request user permissions in runtime */

        String storagePath = Environment.getExternalStorageDirectory().getAbsolutePath();
        String rootPath = storagePath + "/test";
        String fileName = "/test.zip";

        File root = new File(rootPath);
        if(!root.mkdirs()) {
            Log.i("Test", "This path is already exist: " + root.getAbsolutePath());
        }

        File file = new File(rootPath + fileName);
        try {
            int permissionCheck = ContextCompat.checkSelfPermission(MainActivity.this, android.Manifest.permission.WRITE_EXTERNAL_STORAGE);
            if (permissionCheck == PackageManager.PERMISSION_GRANTED) {
                if (!file.createNewFile()) {
                    Log.i("Test", "This file is already exist: " + file.getAbsolutePath());
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @TargetApi(23)
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case 100:
                if (grantResults.length > 0
                        || grantResults[0] == PackageManager.PERMISSION_GRANTED
                        || grantResults[1] == PackageManager.PERMISSION_GRANTED) {
                    /* User checks permission. */

                } else {
                    Toast.makeText(MainActivity.this, "Permission is denied.", Toast.LENGTH_SHORT).show();
                    finish();
                }
                //return; // delete.
        }
    }
}

It works!

回答2:

I was having the same problem. I got an IOException on the file.createNewFile. A closer look at the exception reveals that it was due to "permissions denied". I was writing to my getFilesDir, so I shouldn't need an in the android manifest to accomplish this task. I of course added both READ and WRITE permissions for external storage, and of course, that didn't fix the problem.

I had been testing the code using a NEXUS 6 emulator with sdk 26. Without changing any code, I tried testing using a PIXEL C emulator with sdk 26 and the problem did not occur. So there seems to be some problem with my Nexus 6 emulator.

I suspect that this hasn't always been a problem and that this emulator instance got corrupted, but I haven't verified that. I did take the time to look at the linux file permission on the directories I was creating the file into an it reported "drwxrwxrwx", which is correct. I will add that I've implemented a FileProvider with paths to the directory I'm trying to create the new file at. The code I'm using pretty much looks like the code that Kae10 shows.

I traced the problem down to this code in UnixFileSystem:

public boolean createFileExclusively(String path) throws IOException {
    BlockGuard.getThreadPolicy().onWriteToDisk();
    return createFileExclusively0(path);
}

the exception is thrown from createFileExlussively0, which I not able to debug into. I haven't investigated this issue any further (i.e. 1.) would deleting the avd instance and recreating it help, my guess is that might, 2.) is there a later system image I should be using?)

来源：https://stackoverflow.com/questions/34651771/file-createnewfile-method-throws-exception-in-android-m

标签

java

android

file

ioexception

runtime-permissions