Android - 刚刚创建的错误打开文件

Question

I'm new to android developement and trying to do some file IO. Whenever I run this block of code:

File meta = new File(context.getAppContext().getFilesDir(),"meta");
meta.mkdirs();
File dir = new File(meta,"subdir");
File imageFile = new File(dir,"filename");
Log.d("test",imageFile.getAbsolutePath());
FileOutputStream outputStream = new FileOutputStream(imageFile);

I get this error:

    java.io.FileNotFoundException: /data/data/com.example.android.networkusage/files/meta/Greg and The Morning Buzz/artwork30.jpg: open failed: ENOENT (No such file or directory)
    at libcore.io.IoBridge.open(IoBridge.java:406)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:88)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:73)
    at com.example.android.networkusage.Podcast.downloadArtworkFromUrl(Podcast.java:117)
    at com.example.android.networkusage.Podcast.<init>(Podcast.java:93)
    at com.example.android.networkusage.JSONParser.parse(JSONParser.java:113)
    at com.example.android.networkusage.NetworkActivity.loadXmlFromNetwork(NetworkActivity.java:240)
    at com.example.android.networkusage.NetworkActivity.access$100(NetworkActivity.java:65)
    at com.example.android.networkusage.NetworkActivity$DownloadXmlTask.doInBackground(NetworkActivity.java:203)
    at com.example.android.networkusage.NetworkActivity$DownloadXmlTask.doInBackground(NetworkActivity.java:198)
    at android.os.AsyncTask$2.call(AsyncTask.java:264)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
    at java.lang.Thread.run(Thread.java:856)
    Caused by: libcore.io.ErrnoException: open failed: ENOENT (No such file or directory)
    at libcore.io.Posix.open(Native Method)
    at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110)
    at libcore.io.IoBridge.open(IoBridge.java:390)
    ... 16 more

The log even prints out the file's path as directed, so the file must exist! Why is this happening?

Also, my app has internal and external write priviledges.

Answer 1

One of the sub-directories ( subdir ) and file do not exist. The code should call createNewFile() to actually create the file. Also the subdir directory needs to be made by calling mkdirs() .

File meta = new File(context.getAppContext().getFilesDir(),"meta")
meta.mkdirs();
File dir = new File(meta, "subdir");
dir.mkdirs(); //added
File imageFile = new File(dir, "filename.txt");
imageFile.createNewFile(); //added
FileOutputStream outputStream = new FileOutputStream(imageFile);

I do not believe the File constructor actually creates the file on the file system. The documentation states:

Instances of this class may or may not denote an actual file-system object such as a file or a directory. If it does denote such an object then that object resides in a partition. A partition is an operating system-specific portion of storage for a file system. A single storage device (eg a physical disk-drive, flash memory, CD-ROM) may contain multiple partitions. The object, if any, will reside on the partition named by some ancestor of the absolute form of this pathname.

Answer 2

this is a snippet of code from a project i'm working on right now :

from inside an activity/context :

File dir = getDir("Foler", 0);        // i think your problem is here
File file = new File(dir,"File.bin");

creating directory in android is different than java on normal computer, try to create your directory using getDir() instead of new File(...).mkdirs(), and make sure it is from inside a context (after the activity is created)

i dont believe i'm the best one to answer this question since i'm new to android as well, but maybe this helps

so final code maybe like this

File dir = getDir("subdir",0);
File imageFile = new File(dir, "filename.txt");
imageFile.createNewFile();
FileOutputStream outputStream = new FileOutputStream(imageFile);

i dont know about making nested directories, i didnt try it up till now