Android - 刚刚创建的错误打开文件

Question

我是android developpement的新手,并尝试做一些文件IO.每当我运行这段代码时:

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);

我收到此错误:

    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

日志甚至按照指示打印出文件的路径,因此文件必须存在!为什么会这样？

此外,我的应用程序具有内部和外部写入权限.

Answer 1

其中一个子目录(subdir)和文件不存在.代码应该调用createNewFile()实际创建文件.此subdir目录也需要通过调用来完成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);

我不相信File构造函数实际上在文件系统上创建文件.文件说明:

此类的实例可能表示也可能不表示实际的文件系统对象,例如文件或目录.如果它确实表示这样的对象,则该对象驻留在分区中.分区是文件系统的特定于操作系统的存储部分.单个存储设备(例如,物理磁盘驱动器,闪存,CD-ROM)可以包含多个分区.该对象(如果有)将驻留在由此路径名的绝对形式的某个祖先命名的分区上.