如何在Android下载pdf文件？

时间：2011-06-16 08:00:09

标签： android download

我想从网址下载pdf文件。 为了查看pdf文件，我使用了以下代码。

File file = new File("/sdcard/example.pdf");

if (file.exists()) {
    Uri path = Uri.fromFile(file);
    Intent intent = new Intent(Intent.ACTION_VIEW);
    intent.setDataAndType(path, "application/pdf");
    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

    try {
        startActivity(intent);
    } 
    catch (ActivityNotFoundException e) {
        Toast.makeText(OpenPdf.this, "No Application Available to View PDF",
            Toast.LENGTH_SHORT).show();
    }
}

它正在运行，但如何从网址获取pdf文件（例如http://.../example.pdf）。我想从此网址下载 pdf文件。请帮我。提前谢谢。

5 个答案:

答案 0 :(得分：20)

下载pdf：

 startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("www.education.gov.yk.ca/pdf/pdf-test.pdf")));

啊，因为我刚刚发现这取决于设备。

<强>场景

  1. 它会将pdf下载到您的浏览器/已下载/文件夹

  2. 您有一个Google文档帐户 - 它会要求您登录，然后在浏览器中查看pdf

  3. 您安装了PDF阅读器 - 依赖于应用程序可能无法识别

    4. 在所有情况下，尽管用户可以使用一行代码访问PDF： - ）

答案 1 :(得分：9)

下载PDF与下载任何其他二进制文件的工作方式相同。

  1. 打开HttpUrlConnection
  2. 使用连接的getInputStream()方法读取文件。
  3. 创建FileOutputStream并编写输入流。

    4. 检查this post示例源代码。

答案 2 :(得分：9)

下载文件的方法有很多种。以下我将发布最常见的方式;您可以自行决定哪种方法更适合您的应用。

1。使用AsyncTask并在对话框中显示下载进度

此方法允许您同时执行一些后台进程并更新UI（在这种情况下，我们将更新进度条）。

这是一个示例代码：

// declare the dialog as a member field of your activity
ProgressDialog mProgressDialog;

// instantiate it within the onCreate method
mProgressDialog = new ProgressDialog(YourActivity.this);
mProgressDialog.setMessage("A message");
mProgressDialog.setIndeterminate(true);
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setCancelable(true);

// execute this when the downloader must be fired
final DownloadTask downloadTask = new DownloadTask(YourActivity.this);
downloadTask.execute("the url to the file you want to download");

mProgressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
    @Override
    public void onCancel(DialogInterface dialog) {
        downloadTask.cancel(true);
    }
});

AsyncTask将如下所示：

// usually, subclasses of AsyncTask are declared inside the activity class.
// that way, you can easily modify the UI thread from here
private class DownloadTask extends AsyncTask<String, Integer, String> {

    private Context context;
    private PowerManager.WakeLock mWakeLock;

    public DownloadTask(Context context) {
        this.context = context;
    }

    @Override
    protected String doInBackground(String... sUrl) {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            // expect HTTP 200 OK, so we don't mistakenly save error report
            // instead of the file
            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                return "Server returned HTTP " + connection.getResponseCode()
                        + " " + connection.getResponseMessage();
            }

            // this will be useful to display download percentage
            // might be -1: server did not report the length
            int fileLength = connection.getContentLength();

            // download the file
            input = connection.getInputStream();
            output = new FileOutputStream("/sdcard/file_name.extension");

            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                // allow canceling with back button
                if (isCancelled()) {
                    input.close();
                    return null;
                }
                total += count;
                // publishing the progress....
                if (fileLength > 0) // only if total length is known
                    publishProgress((int) (total * 100 / fileLength));
                output.write(data, 0, count);
            }
        } catch (Exception e) {
            return e.toString();
        } finally {
            try {
                if (output != null)
                    output.close();
                if (input != null)
                    input.close();
            } catch (IOException ignored) {
            }

            if (connection != null)
                connection.disconnect();
        }
        return null;
    }

上述方法（doInBackground）始终在后台线程上运行。你不应该在那里做任何UI任务。另一方面，onProgressUpdate和onPreExecute在UI线程上运行，因此您可以更改进度条：

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // take CPU lock to prevent CPU from going off if the user 
        // presses the power button during download
        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
             getClass().getName());
        mWakeLock.acquire();
        mProgressDialog.show();
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        // if we get here, length is known, now set indeterminate to false
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setMax(100);
        mProgressDialog.setProgress(progress[0]);
    }

    @Override
    protected void onPostExecute(String result) {
        mWakeLock.release();
        mProgressDialog.dismiss();
        if (result != null)
            Toast.makeText(context,"Download error: "+result, Toast.LENGTH_LONG).show();
        else
            Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show();
    }

要运行此功能，您需要WAKE_LOCK权限。

<uses-permission android:name="android.permission.WAKE_LOCK" />

2。从服务下载

这里最大的问题是：如何从服务更新我的活动？。在下一个示例中，我们将使用您可能不知道的两个类：ResultReceiver和IntentService。 ResultReceiver允许我们从服务更新我们的线程; IntentService是Service的子类，它产生一个线程来从那里开始后台工作（你应该知道Service实际上在你的app的同一个线程中运行;当你扩展Service时1}}，你必须手动生成新线程来运行CPU阻塞操作。）

下载服务可能如下所示：

public class DownloadService extends IntentService {
    public static final int UPDATE_PROGRESS = 8344;
    public DownloadService() {
        super("DownloadService");
    }
    @Override
    protected void onHandleIntent(Intent intent) {
        String urlToDownload = intent.getStringExtra("url");
        ResultReceiver receiver = (ResultReceiver) intent.getParcelableExtra("receiver");
        try {
            URL url = new URL(urlToDownload);
            URLConnection connection = url.openConnection();
            connection.connect();
            // this will be useful so that you can show a typical 0-100% progress bar
            int fileLength = connection.getContentLength();

            // download the file
            InputStream input = new BufferedInputStream(connection.getInputStream());
            OutputStream output = new FileOutputStream("/sdcard/BarcodeScanner-debug.apk");

            byte data[] = new byte[1024];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                total += count;
                // publishing the progress....
                Bundle resultData = new Bundle();
                resultData.putInt("progress" ,(int) (total * 100 / fileLength));
                receiver.send(UPDATE_PROGRESS, resultData);
                output.write(data, 0, count);
            }

            output.flush();
            output.close();
            input.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        Bundle resultData = new Bundle();
        resultData.putInt("progress" ,100);
        receiver.send(UPDATE_PROGRESS, resultData);
    }
}

将服务添加到您的清单：

<service android:name=".DownloadService"/>

活动将如下所示：

// initialize the progress dialog like in the first example

// this is how you fire the downloader
mProgressDialog.show();
Intent intent = new Intent(this, DownloadService.class);
intent.putExtra("url", "url of the file to download");
intent.putExtra("receiver", new DownloadReceiver(new Handler()));
startService(intent);

以下是ResultReceiver来玩：

private class DownloadReceiver extends ResultReceiver{
    public DownloadReceiver(Handler handler) {
        super(handler);
    }

    @Override
    protected void onReceiveResult(int resultCode, Bundle resultData) {
        super.onReceiveResult(resultCode, resultData);
        if (resultCode == DownloadService.UPDATE_PROGRESS) {
            int progress = resultData.getInt("progress");
            mProgressDialog.setProgress(progress);
            if (progress == 100) {
                mProgressDialog.dismiss();
            }
        }
    }
}

2.1使用Groundy库

Groundy是一个基本上可以帮助您在后台服务中运行代码段的库，它基于上面显示的ResultReceiver概念。此库目前已弃用。这就是整个代码的样子：

您正在显示对话框的活动...... 

public class MainActivity extends Activity {

    private ProgressDialog mProgressDialog;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        findViewById(R.id.btn_download).setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                String url = ((EditText) findViewById(R.id.edit_url)).getText().toString().trim();
                Bundle extras = new Bundler().add(DownloadTask.PARAM_URL, url).build();
                Groundy.create(DownloadExample.this, DownloadTask.class)
                        .receiver(mReceiver)
                        .params(extras)
                        .queue();

                mProgressDialog = new ProgressDialog(MainActivity.this);
                mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                mProgressDialog.setCancelable(false);
                mProgressDialog.show();
            }
        });
    }

    private ResultReceiver mReceiver = new ResultReceiver(new Handler()) {
        @Override
        protected void onReceiveResult(int resultCode, Bundle resultData) {
            super.onReceiveResult(resultCode, resultData);
            switch (resultCode) {
                case Groundy.STATUS_PROGRESS:
                    mProgressDialog.setProgress(resultData.getInt(Groundy.KEY_PROGRESS));
                    break;
                case Groundy.STATUS_FINISHED:
                    Toast.makeText(DownloadExample.this, R.string.file_downloaded, Toast.LENGTH_LONG);
                    mProgressDialog.dismiss();
                    break;
                case Groundy.STATUS_ERROR:
                    Toast.makeText(DownloadExample.this, resultData.getString(Groundy.KEY_ERROR), Toast.LENGTH_LONG).show();
                    mProgressDialog.dismiss();
                    break;
            }
        }
    };
}

Groundy 用于下载文件并显示进度的GroundyTask实现：

public class DownloadTask extends GroundyTask {    
    public static final String PARAM_URL = "com.groundy.sample.param.url";

    @Override
    protected boolean doInBackground() {
        try {
            String url = getParameters().getString(PARAM_URL);
            File dest = new File(getContext().getFilesDir(), new File(url).getName());
            DownloadUtils.downloadFile(getContext(), url, dest, DownloadUtils.getDownloadListenerForTask(this));
            return true;
        } catch (Exception pokemon) {
            return false;
        }
    }
}

然后将其添加到清单中：

<service android:name="com.codeslap.groundy.GroundyService"/>

我认为这不容易。只需抓住最新的jar from Github就可以了。请注意， Groundy 的主要目的是在后台服务中调用外部REST apis，并轻松地将结果发布到UI。如果你在你的应用程序中做了类似的事情，它可能真的很有用。

2.2使用https://github.com/koush/ion

3。使用DownloadManager类（仅GingerBread和更新版本）

GingerBread带来了一个新功能DownloadManager，它允许您轻松下载文件并将处理线程，流等的艰苦工作委派给系统。

首先，让我们看一个实用方法：

/**
 * @param context used to check the device version and DownloadManager information
 * @return true if the download manager is available
 */
public static boolean isDownloadManagerAvailable(Context context) {

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) {
        return true;
    }
    return false;
}

方法的名称解释了这一切。一旦确定DownloadManager可用，就可以执行以下操作：

String url = "url you want to download";
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
request.setDescription("Some descrition");
request.setTitle("Some title");
// in order for this if to run, you must use the android 3.2 to compile your app
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
    request.allowScanningByMediaScanner();
    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
}
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "name-of-the-file.ext");

// get download service and enqueue file
DownloadManager manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
manager.enqueue(request);

下载进度将显示在通知栏中。

最后的想法

第一种和第二种方法只是冰山一角。如果您希望自己的应用程序功能强大，那么您需要记住很多事情。这是一个简短的清单：

  • 您必须检查用户是否有可用的互联网连接
  • 确保您拥有正确的权限（INTERNET和WRITE_EXTERNAL_STORAGE）;如果您想查看互联网可用性，还可以ACCESS_NETWORK_STATE。
  • 确保目录下载文件存在并具有写入权限。
  • 如果下载太大，您可能希望实现一种方法，以便在以前的尝试失败时恢复下载。
  • 如果您允许用户中断下载，用户将不胜感激。

除非您需要详细控制下载过程，否则请考虑使用DownloadManager（3），因为它已经处理了上面列出的大多数项目。

但也要考虑您的需求可能会发生变化。例如，DownloadManager does no response caching。它会盲目地多次下载同一个大文件。事后并没有简单的方法来解决它。如果您从基本HttpURLConnection（1,2）开始，那么您只需要添加HttpResponseCache。因此，学习基本标准工具的初步努力可能是一项很好的投资。

答案 3 :(得分：1)

没有必要在android中打开和下载pdf冗长的代码你可以使用下面的代码来打开和下载pdf 

String URL ="http://worldhappiness.report/wp-content/uploads/sites/2/2016/03/HR-V1_web.pdf"

 startActivity(new Intent(Intent.ACTION_VIEW,Uri.parse(URL)));

答案 4 :(得分：0)

public static class Downloader {

 public static void DownloadFile(String fileURL, File directory) {
    try {
         FileOutputStream file = new FileOutputStream(directory);
         URL url = new URL(fileURL);
        HttpURLConnection connection = (HttpURLConnection) url .openConnection();
         connection .setRequestMethod("GET");
         connection .setDoOutput(true);
         connection .connect();
         InputStream input = connection .getInputStream();
         byte[] buffer = new byte[1024];
         int len = 0;
          while ((len = input .read(buffer)) > 0) {
           file .write(buffer, 0, len );
         }
        file .close();
  } catch (Exception e) {
          e.printStackTrace();
   }
}

如需了解更多信息，请点击此处http://androiddhina.blogspot.in/2015/09/how-to-download-pdf-from-url-in-android.html

相关问题
最新问题