When it is not present, then the response is usually just been transferred using chunked encoding. That's true, if you inspect the response to that url request in firebug you will see that the content-length is not present — Fgblanch. Sean Patrick Floyd Sean Patrick Floyd k 60 60 gold badges silver badges bronze badges. If I add in the stuff that's actually required to make your code run e. Same styles for both. I'd say mine is shorter and yours has more dependencies. I can post it if you wish.
But that's not my point: I prefer to use descriptive high level methods where everybody immediately sees what the code does, you use highly efficient but not very communicative code.
Yes: your code probably performs better, but mine is more readable and more maintainable for inexperienced developers. I'd say both approaches are valid. Yeah, like I said I can post it. I can edit your answer so you can see. There's other stuff in there, and I tend to have a style that doesn't minimize lines, but it's similar for both. I doubt that there's a performance difference: the network download swamps any micro-optimizations we might make.
I'd guess that your library code is more performant. And your point is well taken about readability. I was just curious about your "fewer lines of code" claim. Not true, so that's not the deciding factor. What I did was to past each of our codes into eclipse and let the formatter with my standard settings do it's magic without changing the results I took your main method and pasted into my existing class.
So yes, the results are biased by my formatter settings. I'd be interested in your version, if you have the time. Measured performance - it was a wash. Show 1 more comment. Sign up or log in Sign up using Google. Sign up using Facebook. When we read a large number of bytes, the application performance will be poor, due to a large number of context switches involved. For writing the bytes read from the URL to our local file, we'll use the write method from the FileOutputStream class:.
When using a BufferedInputStream, the read method will read as many bytes as we set for the buffer size. In our example, we're already doing this by reading blocks of bytes at a time, so BufferedInputStream isn't necessary. The example above is very verbose, but luckily, as of Java 7, we have the Files class which contains helper methods for handling IO operations. We can use the Files. Our code works well but can be improved.
Its main drawback is the fact that the bytes are buffered into memory. Fortunately, Java offers us the NIO package that has methods to transfer bytes directly between 2 Channels without buffering. The Java NIO package offers the possibility to transfer bytes between 2 Channels without buffering them into the application memory.
The bytes read from the ReadableByteChannel will be transferred to a FileChannel corresponding to the file that will be downloaded:. The transferTo and transferFrom methods are more efficient than simply reading from a stream using a buffer. Depending on the underlying operating system, the data can be transferred directly from the filesystem cache to our file without copying any bytes into the application memory. On Linux and UNIX systems, these methods use the zero-copy technique that reduces the number of context switches between the kernel mode and user mode.
We've seen in the examples above how we can download content from a URL just by using the Java core functionality. We also can leverage the functionality of existing libraries to ease our work, when performance tweaks aren't needed. We could wrap all the logic into a Callable , or we could use an existing library for this. Notice that we've overridden the onBodyPartReceived method.
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. The code snippet that creates a new HTTP client is as follows:. We then need to create an HttpGet or HttpPost object to send the request to the server.
The request is created by the following line of code:. The execute request function is applied to the client object and returns with a response from the server. Once the request is sent to the server we need a response object to receive the data sent from the server. To catch the response from the server we use the HttpResponse class object. The data sent by the server in the form of a message is obtained through the getEntity function.
You can also obtain the response code sent by the server through the response object and use it to your specific need. The data to be downloaded is encapsulated within the entity object and can be extracted using the getContent function. The getContent function returns an InputStream object that can be further used with a BufferedInputStreamReader to enhance performance.
Now all you need to do is read from the stream byte by byte and write the contents into a file using the FileOutputStream class.
The last thing required to be done is closing all the open resources in order to ensure that the system resources are not overutilized and that there are no memory leaks.
So there you have it - these are the simplest ways to download a file using the basic Java code and other third party libraries. Now that we are done with the basics, you can be as creative as you want and utilize the knowledge to suit your needs.
So see you next time with a new set of concepts to help you become a better coder. We wish you happy coding till then. Free eBook: Git Essentials Check out our hands-on, practical guide to learning Git, with best-practices, industry-accepted standards, and included cheat sheet.
0コメント