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。
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
它会将pdf下载到您的浏览器/已下载/文件夹
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
您安装了PDF阅读器 - 依赖于应用程序可能无法识别
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。
HttpUrlConnection getInputStream()方法读取文件。FileOutputStream并编写输入流。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。
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" />
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();
}
}
}
}
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。
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。
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：
INTERNET和WRITE_EXTERNAL_STORAGE）;如果您想查看互联网可用性，还可以ACCESS_NETWORK_STATE。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