The contents are read as bytes and copied to a file in the local directory using the FileOutputStream. To lower the number of lines of code we can use the Files class available from Java 7. The Files class contains methods that read all the bytes at once and then copies it into another file.
Here is how you can use it:. Java NIO is an alternative package to handle networking and input-output operations in Java. The main advantage that the Java NIO package offers is that it's non-blocking, and has channeling and buffering capabilities. When we use the Java IO library we work with streams that read data byte by byte. However, the Java NIO package uses channels and buffers. The buffering and channeling capabilities allow the system to copy contents from a URL directly into the intended file without needing to save the bytes in application memory, which would be an intermediary step.
The ability to work with channels boosts performance. The downloaded contents will be transferred to a file on the local system via the corresponding file channel.
After defining the file channel we will use the transferFrom method to copy the contents read from the readChannel object to the file destination using the writeChannel object. The transferFrom and transferTo methods are much more efficient than working with streams using a buffer. The transfer methods enable us to directly copy the contents of the file system cache to the file on the system.
Thus direct channeling restricts the number of context switches required and enhances the overall code performance. Now, in the following sections, we will be looking at ways to download files from a URL using third-party libraries instead of core Java functionality components. Now you may be thinking why would we use this when Java has its own set of libraries to handle IO operations.
However, Apache Commons IO overcomes the problem of code rewriting and helps avoid writing boilerplate code. In order to start using the Apache Commons IO library, you will need to download the jar files from the official website.
When you are done downloading the jar files, you need to add them to use them. If you are using an Integrated Development Environment IDE such as Eclipse , you will need to add the files to the build path of your project. There is only a single line of code required to download a file, which looks like:.
The connection and read timeouts convey the permissible time for which either the connection may stay idle or reading from the URL may stop. We will use the copy inputStream, fileOS method to download a file into the local system. Check out our hands-on, practical guide to learning Git, with best-practices, industry-accepted standards, and included cheat sheet. Stop Googling Git commands and actually learn it!
The function returns the number of bytes copied. If the value of the variable i is -1, then it indicates that the contents of the file are over 2GB. When the returned value is -1, you can use the function copyLarge inputStream, fileOS in place of the copy inputstream, fileOS function to handle this load. Both of these functions buffer the inputstream internally. The internal buffer means we do not have to use the BufferedInputStream class to enhance our code performance and helps us avoid writing boilerplate code.
Another library managed by the Apache organization is the HttpComponents package. This library uses the request-response mechanism to download the file from a given URL.
The first step to downloading a file is to create an HTTP client object that would issue the request to the server. For this, we will be using the CloseableHttpClient class. Keep in mind that Groundy 's main purpose is to make calls to external REST apis in a background service and post results to the UI with easily. If you are doing something like that in your app, it could be really useful.
GingerBread brought a new feature, DownloadManager , which allows you to download files easily and delegate the hard work of handling threads, streams, etc. Method's name explains it all. Once you are sure DownloadManager is available, you can do something like this:. First and second methods are just the tip of the iceberg. There are lots of things you have to keep in mind if you want your app to be robust.
Here is a brief list:. Unless you need detailed control of the download process, then consider using DownloadManager 3 because it already handles most of the items listed above. But also consider that your needs may change. For example, DownloadManager does no response caching. It will blindly download the same big file multiple times. There's no easy way to fix it after the fact.
So the initial effort of learning the basic, standard tools can be a good investment. This class was deprecated in API level ProgressDialog is a modal dialog, which prevents the user from interacting with the app. Instead of using this class, you should use a progress indicator like ProgressBar, which can be embedded in your app's UI.
Alternatively, you can use a notification to inform the user of the task's progress. For more details Link. Don't forget to add permissions to your manifest file if you're gonna be downloading stuff from the internet!
Yes the code above will work. But if you are updating your progressbar in onProgressUpdate of Asynctask and you press back button or finish your activity AsyncTask looses its track with your UI.
And when you go back to your activity, even if download is running in background you will see no update on progressbar. So on OnResume try to run a thread like runOnUIThread with a timer task that updates ur progressbar with values updating from the AsyncTask running background.
I'd recommend you to use my Project Netroid , It's based on Volley. I have added some features to it such as multi-events callback, file download management.
This could be of some help. I have modified AsyncTask class to handle creation of progressDialog at the same context. I think following code will be more reusable. I found this blog post very helpful, Its using loopJ to download file, it has only one Simple function, will be helpful to some new android guys.
While I was starting to learn android development, I had learnt that ProgressDialog is the way to go. There is the setProgress method of ProgressDialog which can be invoked to update the progress level as the file gets downloaded.
The best I have seen in many apps is that they customize this progress dialog's attributes to give a better look and feel to the progress dialog than the stock version. Any animation with in the progress dialog attracts users and they don't feel like being kept waiting for long. My personal advice is to use Progress Dialog and build up before execution , or initiate at OnPreExecute , publish progress often if you use horizontal style of progress bar of the progress dialog.
The remaining part is to optimize the algorithm of doInBackground. Use Android Query library, very cool indeed. You can change it to use ProgressDialog as you see in other examples, this one will show progress view from your layout and hide it after completion.
I am adding another answer for other solution I am using now because Android Query is so big and unmaintained to stay healthy. You can observer the progress of the download manager using LiveData and coroutines, see the gist below. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 11 years, 5 months ago. Active 7 months ago.
Viewed k times. Improve this question. Tom Leese Tom Leese I hope below link may be help you For quick fix refer this answer — Richa. Add a comment. Active Oldest Votes. Use AsyncTask and show the download progress in a dialog This method will allow you to execute some background processes and update the UI at the same time in this case, we'll update a progress bar.
Imports: import android. PowerManager; import java. InputStream; import java. OutputStream; import java. FileOutputStream; import java. Download from Service The big question here is: how do I update my activity from a service? This is how the whole code would look like: The activity where you are showing the dialog Use DownloadManager class GingerBread and newer only GingerBread brought a new feature, DownloadManager , which allows you to download files easily and delegate the hard work of handling threads, streams, etc.
Request Uri. Final thoughts First and second methods are just the tip of the iceberg. Make sure the directory were you are going to download files exist and has write permissions. If download is too big you may want to implement a way to resume the download if previous attempts failed. Users will be grateful if you allow them to interrupt the download.
Improve this answer. There is a problem in Cristian's answer. Because code at " 1. Use AsyncTask and show the download progress in a dialog " does connection. Suggested to close the streams input and output in finally instead of try , otherwise if any exception is thrown before close , you have unclosed streams hanging around.
Show 55 more comments. Ziem 6, 7 7 gold badges 50 50 silver badges 85 85 bronze badges. Mnightmare Mnightmare 1, 1 1 gold badge 10 10 silver badges 6 6 bronze badges. This is exactly my problem. Can you tell me how to do a timer task to update progressbar? How to get values updating from the AsyncTask running behind — user And when u restart the activity where u want to update ur UI run the UI thread..
The UI should have the fresh reference.. Like the newly initalized ProgressBar in my case — sheetal. My device is Xperia P with Android 4. I've defined a static boolean variable that the onPreExecute sets it to true and the onPostExecute sets it to false.
It shows that we are downloading or not, so we can check if the variable is equal to true, show the previous progressbar dialog.
Show 2 more comments. VinceStyling VinceStyling 3, 2 2 gold badges 26 26 silver badges 42 42 bronze badges. Does it support multiple file download? I'm working on a project that allow user to download scheduled. At a specific time 12 AM for instance , the service will download all the link that user selected before.
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