Android - 如何从网络服务器下载文件

Question

在我的应用程序中我从webserver下载kml文件。我已经在我的android清单文件中设置了外部存储和互联网的权限。我是android的新手，非常感谢你的帮助

MainActivity.java

package com.example.demo;

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

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.Menu;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DownloadFiles();
    }
    public void DownloadFiles(){

            try {
                URL u = new URL("http://www.qwikisoft.com/demo/ashade/20001.kml");
                InputStream is = u.openStream();

                DataInputStream dis = new DataInputStream(is);

                byte[] buffer = new byte[1024];
                int length;

                FileOutputStream fos = new FileOutputStream(new File(Environment.getExternalStorageDirectory() + "/" + "data/test.kml"));
                while ((length = dis.read(buffer))>0) {
                  fos.write(buffer, 0, length);
                }

              } catch (MalformedURLException mue) {
                Log.e("SYNC getUpdate", "malformed url error", mue);
              } catch (IOException ioe) {
                Log.e("SYNC getUpdate", "io error", ioe);
              } catch (SecurityException se) {
                Log.e("SYNC getUpdate", "security error", se);
              }
    }
}

Android清单文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.demo"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="16" />
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <activity
            android:name="com.example.demo.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Logcat错误：

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.demo/com.example.demo.MainActivity}: android.os.NetworkOnMainThreadException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
at java.net.InetAddress.getAllByName(InetAddress.java:220)
at libcore.net.http.HttpConnection.<init>(HttpConnection.java:71)
at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)
at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:351)
at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:86)
at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308)
at libcore.net.http.HttpEngine.connect(HttpEngine.java:303)
at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:273)
at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:168)
at java.net.URL.openStream(URL.java:462)
at com.example.demo.MainActivity.DownloadFiles(MainActivity.java:30)
at com.example.demo.MainActivity.onCreate(MainActivity.java:24)
at android.app.Activity.performCreate(Activity.java:4465)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

修改

package com.example.demo;

import java.io.BufferedInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;

import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;

public class MainActivity extends Activity {

    private ProgressDialog pDialog;
    public static final int progress_bar_type = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        new DownloadFileFromURL().execute("http://www.qwikisoft.com/demo/ashade/20001.kml");

    }

    @Override
    protected Dialog onCreateDialog(int id) {
        switch (id) {
        case progress_bar_type: // we set this to 0
            pDialog = new ProgressDialog(this);
            pDialog.setMessage("Downloading file. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setMax(100);
            pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            pDialog.setCancelable(true);
            pDialog.show();
            return pDialog;
        default:
            return null;
        }
    }


    class DownloadFileFromURL extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Bar Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            showDialog(progress_bar_type);
        }

        /**
         * Downloading file in background thread
         * */
        @Override
        protected String doInBackground(String... f_url) {
            int count;
            try {
                URL url = new URL(f_url[0]);
                URLConnection conection = url.openConnection();
                conection.connect();

                // this will be useful so that you can show a tipical 0-100%
                // progress bar
                int lenghtOfFile = conection.getContentLength();

                // download the file
                InputStream input = new BufferedInputStream(url.openStream(),
                        8192);

                // Output stream
                OutputStream output = new FileOutputStream(Environment
                        .getExternalStorageDirectory().toString()
                        + "/data/downloadedfile.kml");

                byte data[] = new byte[1024];

                long total = 0;

                while ((count = input.read(data)) != -1) {
                    total += count;
                    // publishing the progress....
                    // After this onProgressUpdate will be called
                    publishProgress("" + (int) ((total * 100) / lenghtOfFile));

                    // writing data to file
                    output.write(data, 0, count);
                }

                // flushing output
                output.flush();

                // closing streams
                output.close();
                input.close();

            } catch (Exception e) {
                Log.e("Error: ", e.getMessage());
            }

            return null;
        }

        /**
         * Updating progress bar
         * */
        protected void onProgressUpdate(String... progress) {
            // setting progress percentage
            pDialog.setProgress(Integer.parseInt(progress[0]));
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        @Override
        protected void onPostExecute(String file_url) {
            // dismiss the dialog after the file was downloaded
            dismissDialog(progress_bar_type);

        }
    }
}

当我在模拟器中运行此代码时，代码仍无法正常工作......文件未下载。

Answer 1

使用Async task。 （如果不在4.0中工作则添加

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy); 

）

当您要下载文件时调用：new DownloadFileFromURL().execute(file_url);

public class MainActivity extends Activity {

    // Progress Dialog
    private ProgressDialog pDialog;
    public static final int progress_bar_type = 0;

    // File url to download
    private static String file_url = "http://www.qwikisoft.com/demo/ashade/20001.kml";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        new DownloadFileFromURL().execute(file_url);

    }

    /**
     * Showing Dialog
     * */

    @Override
    protected Dialog onCreateDialog(int id) {
        switch (id) {
        case progress_bar_type: // we set this to 0
            pDialog = new ProgressDialog(this);
            pDialog.setMessage("Downloading file. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setMax(100);
            pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            pDialog.setCancelable(true);
            pDialog.show();
            return pDialog;
        default:
            return null;
        }
    }

    /**
     * Background Async Task to download file
     * */
    class DownloadFileFromURL extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Bar Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            showDialog(progress_bar_type);
        }

        /**
         * Downloading file in background thread
         * */
        @Override
        protected String doInBackground(String... f_url) {
            int count;
            try {
                URL url = new URL(f_url[0]);
                URLConnection conection = url.openConnection();
                conection.connect();

                // this will be useful so that you can show a tipical 0-100%
                // progress bar
                int lenghtOfFile = conection.getContentLength();

                // download the file
                InputStream input = new BufferedInputStream(url.openStream(),
                        8192);

                // Output stream
                OutputStream output = new FileOutputStream(Environment
                        .getExternalStorageDirectory().toString()
                        + "/2011.kml");

                byte data[] = new byte[1024];

                long total = 0;

                while ((count = input.read(data)) != -1) {
                    total += count;
                    // publishing the progress....
                    // After this onProgressUpdate will be called
                    publishProgress("" + (int) ((total * 100) / lenghtOfFile));

                    // writing data to file
                    output.write(data, 0, count);
                }

                // flushing output
                output.flush();

                // closing streams
                output.close();
                input.close();

            } catch (Exception e) {
                Log.e("Error: ", e.getMessage());
            }

            return null;
        }

        /**
         * Updating progress bar
         * */
        protected void onProgressUpdate(String... progress) {
            // setting progress percentage
            pDialog.setProgress(Integer.parseInt(progress[0]));
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        @Override
        protected void onPostExecute(String file_url) {
            // dismiss the dialog after the file was downloaded
            dismissDialog(progress_bar_type);

        }

    }
}

Answer 2

我建议使用Android DownloadManager

DownloadManager downloadmanager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
Uri uri = Uri.parse("http://www.example.com/myfile.mp3");

DownloadManager.Request request = new DownloadManager.Request(uri);
request.setTitle("My File");
request.setDescription("Downloading");
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setVisibleInDownloadsUi(false);
request.setDestinationUri(Uri.parse("file://" + folderName + "/myfile.mp3"));

downloadmanager.enqueue(request);

Answer 3

简单的kotlin版

fun download(link: String, path: String) {
    URL(link).openStream().use { input ->
        FileOutputStream(File(path)).use { output ->
            input.copyTo(output)
        }
    }
}

修改

或作为扩展名

fun String.saveTo(path: String) {
    URL(link).openStream().use { input ->
        FileOutputStream(File(path)).use { output ->
            input.copyTo(output)
        }
    }
}

// ...

"http://example.site/document".saveTo("some/path/file")

Answer 4

在主线程上执行网络操作是不好的做法，这就是您看到NetworkOnMainThreadException的原因。政策阻止了这一点。如果您真的必须进行测试，请将以下内容放入OnCreate：

 StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
 StrictMode.setThreadPolicy(policy); 

请注意，执行此操作是非常糟糕的做法，理想情况下应将您的网络代码移至AsyncTask或Thread。

Answer 5

Mr.Iam4fun你的代码在这里回答..你会用线程......

if (payment?.processable)!

和，然后..

   findViewById(R.id.download).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            new Thread(new Runnable() {
                public void run() {
                    DownloadFiles();
                }
            }).start();

当然，它会起作用..

Answer 6

使用AsyncTask和

将您的下载文件代码放在doinbackground中。

android不再允许在主线程上执行繁重的任务以避免ANR（应用程序没有响应）错误

Answer 7

在线程或AsyncTask中运行这些代码。为了避免重复调用相同的_url（一次为getContentLength（），一次为openStream（）），请使用Apache的IOUtils.toByteArray。

void downloadFile(String _url, String _name) {
    try {
        URL u = new URL(_url);
        DataInputStream stream = new DataInputStream(u.openStream());
        byte[] buffer = IOUtils.toByteArray(stream);
        FileOutputStream fos = mContext.openFileOutput(_name, Context.MODE_PRIVATE);
        fos.write(buffer);
        fos.flush();
        fos.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        return;
    } catch (IOException e) {
        e.printStackTrace();
        return;
    }
}

Answer 8

除了使用AsyncTask之外，您还可以将操作置于runnable -

中

Runnable r=new Runnable()
{

public void run()
{
///-------network operation code
}
};

//--------call r in this way--
Thread t=new Thread(r);`enter code here`
t.start();

Also put the UI work in a haldler..such as updating a textview etc..

Answer 9

从api level 11或Honeycomb开始在主线程上进行网络操作是禁止的。使用线程或asynctask。有关详细信息，请访问https://developer.android.com/reference/android/os/NetworkOnMainThreadException.html

Answer 10

下载文件Usind下载管理器

    DownloadManager downloadmanager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
    Uri uri = Uri.parse("https://www.globalgreyebooks.com/content/books/ebooks/game-of-life.pdf");

    DownloadManager.Request request = new DownloadManager.Request(uri);
    request.setTitle("My File");
    request.setDescription("Downloading");//request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
    request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS,"game-of-life");
    downloadmanager.enqueue(request);

Answer 11

以下代码可帮助您从服务器上下载文件，同时您还可以在状态栏上看到下载进度。

请参见下面代码的功能：

步骤-1：在 DownloadFileFromURL.java 类文件上创建，以从服务器下载文件内容。在这里，我创建了一个异步任务来下载文件。

public class DownloadFileFromURL extends AsyncTask<String, Integer, String> {

private NotificationManager mNotifyManager;
private NotificationCompat.Builder build;
private File fileurl;
int id = 123;
OutputStream output;
private Context context;
private String selectedDate;
private String ts = "";

public DownloadFileFromURL(Context context, String selectedDate) {
    this.context = context;
    this.selectedDate = selectedDate;

}

protected void onPreExecute() {
    super.onPreExecute();

    mNotifyManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    build = new NotificationCompat.Builder(context);
    build.setContentTitle("Download")
            .setContentText("Download in progress")
            .setChannelId(id + "")
            .setAutoCancel(false)
            .setDefaults(0)
            .setSmallIcon(R.drawable.ic_menu_download);

    // Since android Oreo notification channel is needed.
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        NotificationChannel channel = new NotificationChannel(id + "",
                "Social Media Downloader",
                NotificationManager.IMPORTANCE_HIGH);
        channel.setDescription("no sound");
        channel.setSound(null, null);
        channel.enableLights(false);
        channel.setLightColor(Color.BLUE);
        channel.enableVibration(false);
        mNotifyManager.createNotificationChannel(channel);

    }
    build.setProgress(100, 0, false);
    mNotifyManager.notify(id, build.build());
    String msg = "Download started";
    //CustomToast.showToast(context,msg);
}

@Override
protected String doInBackground(String... f_url) {
    int count;
    ts = selectedDate.split("T")[0];
    try {
        URL url = new URL(f_url[0]);
        URLConnection conection = url.openConnection();
        conection.connect();
        int lenghtOfFile = conection.getContentLength();

        InputStream input = new BufferedInputStream(url.openStream(),
                8192);
        // Output stream
        output = new FileOutputStream(Environment
                .getExternalStorageDirectory().toString()
                + Const.DownloadPath + ts + ".pdf");
        fileurl = new File(Environment.getExternalStorageDirectory()
                + Const.DownloadPath + ts + ".pdf");
        byte[] data = new byte[1024];

        long total = 0;

        while ((count = input.read(data)) != -1) {
            total += count;
            int cur = (int) ((total * 100) / lenghtOfFile);

            publishProgress(Math.min(cur, 100));
            if (Math.min(cur, 100) > 98) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    Log.d("Failure", "sleeping failure");
                }
            }
            Log.i("currentProgress", "currentProgress: " + Math.min(cur, 100) + "\n " + cur);

            output.write(data, 0, count);
        }

        output.flush();

        output.close();
        input.close();

    } catch (Exception e) {
        Log.e("Error: ", e.getMessage());
    }

    return null;
}

protected void onProgressUpdate(Integer... progress) {
    build.setProgress(100, progress[0], false);
    mNotifyManager.notify(id, build.build());
    super.onProgressUpdate(progress);
}

@Override
protected void onPostExecute(String file_url) {
    build.setContentText("Download complete");
    build.setProgress(0, 0, false);
    mNotifyManager.notify(id, build.build());
} }

注意：如果您要使用导入包中的代码，请Click Here

现在，第2步：您需要在click事件上调用上述异步任务。例如，我已经设置了pdf图像图标。 要调用AsyncTask，请使用以下代码：

 new DownloadFileFromURL(fContext,filename).execute(serverFileUrl);

注意：在这里您可以在文件参数中看到文件名变量。这是我用来将下载的文件保存在本地设备中的名称。目前，我仅下载pdf文件，但是您可以在 serverFileUrl 参数中使用您的网址。

Answer 12

当你点击下载按钮时，首先你必须创建你想要保存它的本地存储路径，我们应该将下载文件功能放入ExecutorService（使用它代替AsyncTask，因为AsyncTask已被弃用）。

// Create bamchik folder if not created yet
val folder = File(context?.getExternalFilesDir(null)?.absoluteFile, "MusicTrack")
val check = folder.mkdirs()
Log.v(mTAG, "check: $check")
var path = context?.getExternalFilesDir(null)?.absolutePath + "/MusicTrack/music." + fileExt
val SDK_INT = Build.VERSION.SDK_INT
if (SDK_INT > 8) {
    val policy: StrictMode.ThreadPolicy = StrictMode.ThreadPolicy.Builder().permitAll().build()
    StrictMode.setThreadPolicy(policy)
    val executor: ExecutorService = Executors.newSingleThreadExecutor()
    val handler = object : Handler(Looper.getMainLooper()) {
        override fun handleMessage(msg: Message) {
            // Length is the total size of file and progress is how much file have been downloaded, now you can show progress according to this
            val (progress, length) = msg.obj as Pair<Long, Long> 
            Log.v(mTAG, "Progress: $progress, Length: $length")
        }

    }

    executor.execute {
        //Background work here
        download(link, path) { progress, length ->
            // handling the result on main thread
            handler.sendMessage(handler.obtainMessage(0, progress to length))
        }
        handler.post {
            //UI Thread work here
        }
    }
}

从url下载文件的功能

fun download(link: String, path: String, progress: ((Long, Long) -> Unit)? = null): Long {
    val url = URL(link)
    val connection = url.openConnection()
    connection.connect()
    val length = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) connection.contentLengthLong else connection.contentLength.toLong()
    url.openStream().use { input ->
        FileOutputStream(File(path)).use { output ->
            val buffer = ByteArray(DEFAULT_BUFFER_SIZE)
            var bytesRead = input.read(buffer)
            var bytesCopied = 0L
            while (bytesRead >= 0) {
                output.write(buffer, 0, bytesRead)
                bytesCopied += bytesRead
                progress?.invoke(bytesCopied, length)
                bytesRead = input.read(buffer)
            }

            return bytesCopied
        }
    }
}

Answer 13

您应该使用AsyncTask（或其他方式在后台执行网络操作）。

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //create and execute the download task
    MyAsyncTask async = new MyAsyncTask();
    async.execute();

}

private class MyAsyncTask extends AsyncTask<Void, Void, Void>{

    //execute on background (out of the UI thread)
    protected Long doInBackground(URL... urls) {
        DownloadFiles();
    }

}

有关Android documentation

上的AsyncTask的更多信息

希望它有所帮助。