Android - ウェブサーバーからファイルをダウンロードする方法

質問

私のアプリでは kml ファイルをダウンロードしています。アンドロイドマニフェストファイルで、外部ストレージとインターネットに対するパーミッションを設定しました。私はAndroidに新しいです、あなたの助けは非常に感謝されます。

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 マニフェストファイル

<?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のエラーです。

FATAL EXCEPTION: メイン 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)にて。 at android.os.Looper.loop(Looper.java:137)にて。 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)にて。 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)にて。 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)。 at dalvik.system.NativeStart.main(Native Method) 原因：android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099) at java.net.InetAddress.lookupHostByName(InetAddress.java:391)で発生しました。 at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)。 at java.net.InetAddress.getAllByName(InetAddress.java:220)。 at libcore.net.http.HttpConnection.(HttpConnection.java:71) at libcore.net.http.HttpConnection.(HttpConnection.java:50) at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:351)]を実行します。 at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:86)を実行。 at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)を実行しています。 at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308)にて。 at libcore.net.http.HttpEngine.connect(HttpEngine.java:303)にて。 libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)にて確認。 at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)にて。 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)にて。 at android.app.Activity.performCreate(Activity.java:4465)にて。 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)にて。 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)。

EDIT

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);
        }
    }
}

このコードをエミュレータで実行すると、コードはまだ動作しません - ファイルがダウンロードされないのです。

どのように解決するのですか？

使用方法 非同期タスク

ファイルをダウンロードするときに呼び出されます。 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 connection = url.openConnection();
                connection.connect();

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

        }

    }
}

4.0で動作していない場合は、追加してください。

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