To get the size of file from server first you need to connect to the server using URL and HttpURLConnection Class. To get the size of file we use getContentLength() method. As the size of file can be too large we use BigInteger class. You cannot use integer datatype as it can generate an error in case the size of file is greater than 2Gb.
To know more about BigInteger class refer link: BigInteger class in Java
For HttpURLConnection refer link: Java.net.HttpURLConnection Class in Java
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