Download manager written in java

Download manager is a program that helps us download files from Internet efficiently. The program can pause or resume downloads. It also can split the files to be downloaded into 2 or more segments, which are processed in parallel, making the download faster. In this post, I will share with you how I write a download manager program in Java with those features. To download a file, download manager written in java need to create a thread to handle the download so that it will not intercept the GUI thread.

Download manager written in java is the code for run method of the download thread. It is quite simple. Usually we use or As I comment in the code, firstly we open the connection to the server and get the input stream to read the file. Then we have a while loop to read and write a number of bytes of file to disk. To download multiple parts of a file parallelly, we download manager written in java to create multiple threads.

You can download my program at my GitHub:

Each thread is implemented similarly to the simple thread above, except that it needs to download only a part of the downloaded file. To do that, the HttpURLConnection or its super class URLConnection provides us method setRequestProperty to set the range of the bytes we want to download. When we set the range of the bytes, the server only sends that specific segment of the file, hence the BufferInputStream just read normally. I also think that it is good if the size of each part we download is a multiple of block size of hard disk which is usually So, if the download is paused and resumed later, we can use it to set the range of byte request to the server as above.

Here is the full run function of downloading thread:. Note that, before the InputStream read the file, the output file type of RandomAccessFile need to seek to the mStartByte position of the file, then it will start writing at that position.