在安卓上下载文件

Question

我想从我在网上抓取的链接下载文档，我有一个 listview 监听器，所以当我按下列表中的一个项目时，它会返回一个 url，我设置了它，所以 getLink 将是我要下载并设置的pdf文件的链接filenametoo。

getLink = http://www.phivolcs.dost.gov.ph/images/Flyer-eq-and-eq-hazards.pdf
filename = Flyer-eq-and-eq-hazards.pdf

所以我在我的 listview 侦听器中调用它，它假设可以下载但它不工作。 new DownloadFile().execute(getLink, filename);

我有像java.io.IOException: open failed: ENOENT (No such file or directory)这样的错误

主内

private class DownloadFile extends AsyncTask<String, Void, Void>{

   @Override
   protected Void doInBackground(String... strings) {
       String fileUrl = strings[0];   // -> getLink = http://www.phivolcs.dost.gov.ph/images/Flyer-eq-and-eq-hazards.pdf
       String fileName = strings[1];  // -> Flyer-eq-and-eq-hazards.pdf
       String extStorageDirectory = Environment.getDataDirectory().toString();
       File folder = new File(extStorageDirectory, "testthreepdf");
       folder.mkdir();

       File pdfFile = new File(folder, fileName);

       try{
           pdfFile.createNewFile();
       }catch (IOException e){
           e.printStackTrace();
       }
       FileDownloader.downloadFile(fileUrl, pdfFile);
       return null;
   }
}

下载文件

package com.example.boneyflesh.homepage;


import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class FileDownloader {
    private static final int MEGABYTE = 1024 * 1024;

    public static void downloadFile(String fileUrl, File directory) {
        try {

            URL url = new URL(fileUrl);
            HttpURLConnection urlConnection = (HttpURLConnection)  url.openConnection();              
            urlConnection.connect();

            InputStream inputStream = urlConnection.getInputStream();
            FileOutputStream fileOutputStream = new FileOutputStream(directory);
            int totalSize = urlConnection.getContentLength();

            byte[] buffer = new byte[MEGABYTE];
            int bufferLength = 0;
            while ((bufferLength = inputStream.read(buffer)) > 0) {
                fileOutputStream.write(buffer, 0, bufferLength);
            }
            fileOutputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

  }

清单

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="com.example.boneyflesh.homepage">

<!--
     The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
     Google Maps Android API v2, but you must specify either coarse or fine
     location permissions for the 'MyLocation' functionality. 
-->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" ></uses-permission>
<uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>


<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme"
    tools:ignore="AllowBackup">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <!--
         The API key for Google Maps-based APIs is defined as a string resource.
         (See the file "res/values/google_maps_api.xml").
         Note that the API key is linked to the encryption key used to sign the APK.
         You need a different API key for each encryption key, including the release key that is used to
         sign the APK for publishing.
         You can define the keys for the debug and release targets in src/debug/ and src/release/. 
    -->
    <meta-data
        android:name="com.google.android.geo.API_KEY"
        android:value="@string/google_maps_key" />

    <activity
        android:name=".MapsActivity"
        android:label="@string/title_activity_maps" />
    <!--
 ATTENTION: This was auto-generated to add Google Play services to your project for
 App Indexing.  See https://g.co/AppIndexing/AndroidStudio for more information.
    -->
    <meta-data
        android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version" />

    <activity android:name=".GeohazardResults" />
    <activity android:name=".MineralResults" />
    <activity android:name=".LandformResults" />
    <activity android:name=".Downloads"></activity>
</application>

---

编辑

我打电话给useFileAsyncTask(); 然后我收到一个错误FATAL EXCEPTION: AsyncTask #1

构造函数

protected void useFileAsyncTask() {
    DownloadFile task = new DownloadFile(this);
    task.execute();
}

异步任务

private class DownloadFile extends AsyncTask<String, Void, Void>{

   private Context myContextRef;

   public DownloadFile(Context context) {
       myContextRef = context;
   }


   @Override
   protected Void doInBackground(String... strings) {

       //String fileUrl = strings[0];   // -> http://maven.apache.org/maven-1.x/maven.pdf
       //String fileName = strings[1];  // -> maven.pdf
       String extStorageDirectory = myContextRef.getFilesDir().toString();
       //String extStorageDirectory = Environment.getDataDirectory().toString();
       File folder = new File(extStorageDirectory, "testthreepdf");
       folder.mkdir();

       File pdfFile = new File(folder, filename);

       try{
           pdfFile.createNewFile();
       }catch (IOException e){
           e.printStackTrace();
       }
       FileDownloader.downloadFile(getLink, pdfFile);
       return null;
   }
   }

downloadFile 保持不变。

Answer 1

换行

String extStorageDirectory = Environment.getDataDirectory().toString();

到

String extStorageDirectory = context.getFilesDir().toString();

其中context 是您需要提供给AsyncTask 的Context。

Environment.getDataDirectory() 是系统范围的用户数据目录，您不能在其中创建文件，而ontext.getFilesDir() 是您的应用程序的数据目录，您可以在其中创建文件。