java - 单击按钮后如何下载文件(Android Studio)

Question

我最近在我的应用中创建了一个 Activity 。现在我希望用户在他/她想要查看指南时下载一个 .pdf 文件。我想在一个按钮上实现它。知道如何正确执行此操作吗？

下面是我的代码:

public class Exhibitor_Registration_Activity extends AppCompatActivity  {

    Button buttonDownload;

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

        this.setTitle("Buyer Registration");

        Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
        setSupportActionBar(myToolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        myToolbar.setNavigationIcon(R.drawable.ic_arrow_back_white_24dp);

        final Button buttonDownload = (Button) findViewById(R.id.buttonDownload);

        buttonDownload.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View view) {
                try {
                    //this is the file you want to download from the remote server
                    String path ="http://www.manilafame.com/website-assets/downloads/exhibitor-application-kit/local/201704/1-Summary-of-Participation-Details-April-2017_MN_002.pdfp";
                    //this is the name of the local file you will create
                    String targetFileName = null;
                    boolean eof = false;
                    URL u = new URL(path);
                    HttpURLConnection c = (HttpURLConnection) u.openConnection();
                    c.setRequestMethod("GET");
                    c.setDoOutput(true);
                    c.connect();
                    FileOutputStream f = new FileOutputStream(new File("c:\\junk\\"+targetFileName));
                    InputStream in = c.getInputStream();
                    byte[] buffer = new byte[1024];
                    int len1 = 0;
                    while ( (len1 = in.read(buffer)) > 0 ) {
                        f.write(buffer,0, len1);
                    }
                    f.close();
                } catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (ProtocolException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (FileNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
    }
}

我还从here获得了源代码和 here .

Answer 1

如果要断点续传，下载速度...按照这个步骤

创建一个类DownloadManager.java

public class DownloadManager extends AsyncTask<String,String,String>{
String downloadlink,fileDestination;
public static final int ON_INIT=100,ON_ERROR=102,ON_PROGRASS=103,ON_COMPLETED=104,STATUS_DOWNLOADED=1500,STATUS_NOT_YET=1501;
private onUpdateListener onUpdateListener;
private String downloadedPath="";
private long downloaded=0;
private File file;
private String returnData=null;
private File cacheDownloadFile;
public DownloadManager(String downloadlink,String fileDestinationPath){
    this.downloadlink=downloadlink;
    this.fileDestination=fileDestinationPath;
    file=new File(fileDestination, Tools.getFileName(downloadlink));
    cacheDownloadFile=new File(AppCostants.CHACHE_PATH+Tools.getFileName(downloadlink));
    try {
        if(cacheDownloadFile.isFile())
            downloaded=Tools.getFileSize(cacheDownloadFile);
        else
            downloaded=0;
        Log.d("FILE_DOWNLOAD_TAG_p",downloaded+" <- "+cacheDownloadFile.getAbsolutePath());
    } catch (IOException e) {
        e.printStackTrace();
    }
    fireOnUpdate(ON_INIT,"init ...");

}
@Override
protected String doInBackground(String... params) {
    try {
        File dir=new File(fileDestination);
        File chacheDir=new File(AppCostants.CHACHE_PATH);
        if(!chacheDir.isDirectory())
            chacheDir.mkdirs();
        if(!dir.isDirectory()){
            dir.mkdirs();
        }

        if(file.exists()) {
            Log.d("FILE_DOWNLOAD_TAG","File exist return complete");
            return "COMPLETED";//file exist
        }
        if(!cacheDownloadFile.exists()){
            cacheDownloadFile.createNewFile();
        }
        Log.d("FILE_DOWNLOAD_TAG","LINK "+downloadlink);
        URL url=new URL(downloadlink);
        HttpURLConnection urlConnection= (HttpURLConnection) url.openConnection();
        if(downloaded>0)
            urlConnection.setRequestProperty("Range","byte="+downloaded);
        urlConnection.connect();
        int status = urlConnection.getResponseCode();
        InputStream inputStream=urlConnection.getInputStream();
        int totalSize=urlConnection.getContentLength();
        if(totalSize<=downloaded){
            returnData= "COMPLETED";
            publishProgress("File checked "+Tools.getFileName(file.getAbsolutePath()));
            return returnData;
        }
        this.downloadedPath=cacheDownloadFile.getAbsolutePath();
        byte[] buffer=new byte[1024];
        int bufferLength=0;
        FileOutputStream fileOutput=new FileOutputStream(cacheDownloadFile);
        long d=0;
        long starttime=System.currentTimeMillis();
        while ((bufferLength=inputStream.read(buffer))>0){
            fileOutput.write(buffer,0,bufferLength);
            downloaded+=bufferLength;
            d+=bufferLength;
            //String l=" "+Tools.getFileName(file.getAbsolutePath())+" ( "+Tools.convertMemory(downloaded)+" / "+Tools.convertMemory(totalSize)+" )";
            String l="  "+Tools.convertMemory(downloaded)+" / "+Tools.convertMemory(totalSize)+" ( "+getDownloadSpeed(starttime,d)+" )";
            publishProgress(l);
            if(downloaded>=totalSize){
                break;
            }
        }
        Log.d("FILE_DOWNLOAD_TAG","DWONLOADED TO "+downloadedPath+" ("+cacheDownloadFile.length()+")");
        fileOutput.close();
        if(Tools.fileCopy(file,cacheDownloadFile)){
            Log.d("FILE_DOWNLOAD_TAG","file Copied, delete cache");
            cacheDownloadFile.delete();
        }
        returnData="COMPLETED";
    } catch (MalformedURLException e) {
        returnData=null;
        e.printStackTrace();
        publishProgress(e.toString());
        Log.d("###################",e+"");

    } catch (IOException e) {
        returnData=null;
        e.printStackTrace();
        publishProgress(e.toString());
    }

    return returnData;
}

@Override
protected void onProgressUpdate(String... values) {
    super.onProgressUpdate(values);
    fireOnUpdate(ON_PROGRASS,values[0]);
}

@Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    if(s!=null){
        fireOnUpdate(ON_COMPLETED,downloadedPath);
    }else{
        fireOnUpdate(ON_ERROR,"Download failed");
    }
}

public interface onUpdateListener{
    void onUpdate(int code,String message);
}
public void setOnUpdateListener(onUpdateListener onUpdateListener){
    this.onUpdateListener=onUpdateListener;
}
private void fireOnUpdate(int code,String message){
    if(onUpdateListener!=null)
        onUpdateListener.onUpdate(code,message);
}

private String getDownloadSpeed(long starttime,float totalDownloaded) {
    long elapsedTime = System.currentTimeMillis() - starttime;
    //byte :
    float speed=1000f * totalDownloaded / elapsedTime;
    return convert(speed);
}
private String convert(float value){
    long kb=1024
            ,mb=kb*1024
            ,gb=mb*1024;

    if(value<kb){
        String speed=(value+"");
        speed=speed.substring(0,speed.indexOf('.')+2);
        return speed+" B/s";
    }else if(value<mb){
        value=value/kb;
        String speed=(value+"");
        speed=speed.substring(0,speed.indexOf('.'));
        return (speed)+" KB/s";
    }else if(value<gb){
        value=(value/mb);
        String speed=(value+"");
        speed=speed.substring(0,speed.indexOf('.'));
        return speed+" MB/s";
    }
    return "";
}
}

1. 在 onClick() 中使用此代码DownloadManager downloadManager = new DownloadManager(url,filepath);

2. 设置事件

   downloadManager.setOnUpdateListener(new DownloadManager.onUpdateListener() {
   @Override
   public void onUpdate(int code, String message) {
   if (code == DownloadManager.ON_COMPLETED) {
   
                   }
                   if(DownloadManager.ON_PROGRASS==code){}
   
               }
           });
   

3. 开始下载

   downloadManager.execute();
   

4. 库设置

   compile "commons-io:commons-io:+"
   

5. Tools.java

   public static long getFileSize(File file) throws IOException {
   FileOutputStream fileOutputStream=new FileOutputStream(file);
   fileOutputStream.close();
   return file.length();
   }
   public static boolean fileCopy(File dest,File source){
   try {
       FileUtils.copyFile(source,dest);
       return true;
   } catch (IOException e) {
       e.printStackTrace();
       return false;
   }
   }