Android：无法访问存储在SD卡中的文件

Question

我正在研究一个读取存储在SD卡（内部/数据/本地）中的.txt文件的应用程序。我遇到的问题是，它似乎可以访问文件路径，但它不能访问文件本身（尽管它具有读取和写入权限），但会引发FileNotFoundException异常。 这里，我离开你的代码和日志：

String ruta="/data/local/textojson.txt"; 
System.out.println(ruta); 
String cadena="", Jsontx="";    

File sd = Environment.getExternalStorageDirectory(); 
File f = new File(sd.getAbsolutePath(), ruta); 
System.out.println(f); 

BufferedReader entrada; 
try 
{ 
    entrada = new BufferedReader(new FileReader(f)); 
    System.out.println(entrada); 

    try 
    { 
     while((cadena=entrada.readLine())!=null) 
     { 

      Jsontx=cadena; 
     } 
    } catch (IOException e) 
    { 
    // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
} catch (FileNotFoundException e1) 
{ 
// TODO Auto-generated catch block 
    e1.printStackTrace(); 
} 

我已经添加了READ_EXTERNAL_STORAGE权限清单，并且该文件确实存在于该目录中。

02-04 19:26:40.535: E/Trace(20167): error opening trace file: No such file or directory (2) 
02-04 19:26:41.055: I/System.out(20167): /data/local/textojson.txt 
02-04 19:26:41.066: I/System.out(20167): /mnt/sdcard/data/local/textojson.txt 
02-04 19:26:41.066: W/System.err(20167): java.io.FileNotFoundException: /mnt/sdcard/data/local/textojson.txt: open failed: ENOENT (No such file or directory) 
02-04 19:26:41.066: W/System.err(20167): at libcore.io.IoBridge.open(IoBridge.java:416) 
02-04 19:26:41.075: W/System.err(20167): at java.io.FileInputStream.<init>(FileInputStream.java:78) 
02-04 19:26:41.075: W/System.err(20167): at java.io.FileReader.<init>(FileReader.java:42) 
02-04 19:26:41.075: W/System.err(20167): at es.example.jsonarchivo.Adapter.<init>(Adapter.java:47) 
02-04 19:26:41.075: W/System.err(20167): at es.example.jsonarchivo.MainActivity.onCreate(MainActivity.java:27) 
02-04 19:26:41.075: W/System.err(20167): at android.app.Activity.performCreate(Activity.java:5008) 
02-04 19:26:41.085: W/System.err(20167): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
02-04 19:26:41.085: W/System.err(20167): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
02-04 19:26:41.085: W/System.err(20167): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
02-04 19:26:41.085: W/System.err(20167): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
02-04 19:26:41.085: W/System.err(20167): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
02-04 19:26:41.085: W/System.err(20167): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-04 19:26:41.085: W/System.err(20167): at android.os.Looper.loop(Looper.java:137) 
02-04 19:26:41.085: W/System.err(20167): at android.app.ActivityThread.main(ActivityThread.java:4745) 
02-04 19:26:41.095: W/System.err(20167): at java.lang.reflect.Method.invokeNative(Native Method) 
02-04 19:26:41.105: W/System.err(20167): at java.lang.reflect.Method.invoke(Method.java:511) 
02-04 19:26:41.105: W/System.err(20167): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
02-04 19:26:41.105: W/System.err(20167): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
02-04 19:26:41.105: W/System.err(20167): at dalvik.system.NativeStart.main(Native Method) 
02-04 19:26:41.105: W/System.err(20167): Caused by: libcore.io.ErrnoException: open failed: ENOENT (No such file or directory) 
02-04 19:26:41.116: W/System.err(20167): at libcore.io.Posix.open(Native Method) 
02-04 19:26:41.116: W/System.err(20167): at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110) 
02-04 19:26:41.116: W/System.err(20167): at libcore.io.IoBridge.open(IoBridge.java:400) 
02-04 19:26:41.125: W/System.err(20167): ... 18 more 
02-04 19:26:41.125: D/AndroidRuntime(20167): Shutting down VM 
02-04 19:26:41.125: W/dalvikvm(20167): threadid=1: thread exiting with uncaught exception (group=0x40a13300) 
02-04 19:26:41.145: E/AndroidRuntime(20167): FATAL EXCEPTION: main 
02-04 19:26:41.145: E/AndroidRuntime(20167): java.lang.RuntimeException: Unable to start activity ComponentInfo{es.example.jsonarchivo/es.example.jsonarchivo.MainActivity}: java.lang.NullPointerException 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.os.Looper.loop(Looper.java:137) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.ActivityThread.main(ActivityThread.java:4745) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at java.lang.reflect.Method.invokeNative(Native Method) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at java.lang.reflect.Method.invoke(Method.java:511) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at dalvik.system.NativeStart.main(Native Method) 
02-04 19:26:41.145: E/AndroidRuntime(20167): Caused by: java.lang.NullPointerException 
02-04 19:26:41.145: E/AndroidRuntime(20167): at com.android.internal.os.LoggingPrintStream.println(LoggingPrintStream.java:298) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at es.example.jsonarchivo.Adapter.<init>(Adapter.java:70) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at es.example.jsonarchivo.MainActivity.onCreate(MainActivity.java:27) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.Activity.performCreate(Activity.java:5008) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
02-04 19:26:41.145: E/AndroidRuntime(20167): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
02-04 19:26:41.145: E/AndroidRuntime(20167): ... 11 more 
02-04 19:31:41.224: I/Process(20167): Sending signal. PID: 20167 SIG: 9 

我希望我解释得很好，我的母语不是英语。

Answer 1

回顾一下在回答中，

java.io.FileNotFoundException：/mnt/sdcard/data/local/textojson.txt：打开失败：ENOENT（没有这样的文件或目录）

表示该文件不存在。这可以用f.exists()

进行验证。如果问题是权限，你应该得到open failed: EACCES (Permission denied)