【发布时间】：2017-07-12 04:09:44
【问题描述】：
我正在尝试构建一个应用程序，当给定一个 url 时，它可以从 web 下载文件（例如“.jpg”、“.txt”）。它并不是真的要成为一个真实世界的应用程序，而只是一个练习，以帮助我更加熟悉基于网络和 io 的代码。现在我只是从 url 中提取字节，然后将它们转换为字符串并记录下来。然后从那里我想把它写到一个文件中。我现在遇到的问题是我得到一个文件未找到异常，说明访问被拒绝：
07-11 21:03:14.458 19072-20051/com.example.zacharymcdaniel.webdownloader E/AsyncDownload: network errorjava.io.FileNotFoundException: /sdcard/-1157023572 (Permission denied)
java.io.FileNotFoundException: /sdcard/-1157023572 (Permission denied)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
at java.io.FileOutputStream.<init>(FileOutputStream.java:169)
at com.example.zacharymcdaniel.webdownloader.AsyncDownload.doInBackground(AsyncDownload.java:60)
at com.example.zacharymcdaniel.webdownloader.AsyncDownload.doInBackground(AsyncDownload.java:23)
at android.os.AsyncTask$2.call(AsyncTask.java:304)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)
这是我的清单：
<?xml version="1.0" encoding="utf-8"?>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
以及我用来执行下载和写入操作的异步任务实现代码：
public class AsyncDownload extends AsyncTask<Void, Void, Void>{
private static final String TAG = "AsyncDownload";
private static final String STORAGE_LOCATION = "/sdcard/"; //android directory picker is needed
private URL url;
private ArrayList<Byte> bytes = new ArrayList<>();
public AsyncDownload(URL url){
this.url = url;
}
@Override
protected Void doInBackground(Void... params){
try{
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
ByteArrayOutputStream buffer = new ByteArrayOutputStream();
int c;
while ((c = in.read()) != -1){
buffer.write(c);
}
Log.i(TAG, buffer.toString());
Random rand = new Random(4L);
String temp = String.valueOf(rand.nextInt());
String finalLocation = STORAGE_LOCATION + temp;
File file = new File(finalLocation);
file.getParentFile().mkdirs();
file.setWritable(true);
file.setReadable(true);
FileOutputStream fOut = new FileOutputStream(file);
fOut.write(buffer.toByteArray());
fOut.flush();
fOut.close();
FileInputStream fIn = new FileInputStream(finalLocation);
String reRead = new String();
int a;
while ((a = fIn.read()) != -1){
reRead += a;
}
Log.i(TAG, reRead);
//this section is for automatic file naming
/*Random rand = new Random(5L);
String fileNumber = String.valueOf(rand.nextInt());
StringBuilder sb = new StringBuilder();
sb.append(fileNumber).append("download"); //definitely needs work
Log.i(TAG, sb.toString());*/
//FileOutputStream fOut = new FileOutputStream()
}catch (IOException ioe){
Log.e(TAG, "network error" + ioe.toString(), ioe);
}
return null;
}
}
我对此很陌生，所以我可能犯了一些非常明显的错误。请帮助解决此错误。谢谢。
【问题讨论】：
-
您在哪个 api 级别上运行？从 6.0 或更高版本开始，如果您写入外部存储，则必须询问用户运行时以获得许可。如果您写入应用特定的存储空间，则不需要它。
-
如果你是在安卓6以上的设备上测试，你需要请求读写权限
-
你确定路径正确吗？
标签： java android android-permissions filenotfoundexception