File Downloader

file-downloader is a small Java CLI project for downloading chunks of a file in parallel over HTTP/HTTPS, developed for a JetBrains internship application. It supports:

• Sequential download (threads = 1, avoids the overhead of creating threads => good for small files)
• Parallel range download (threads > 1, good for large files)

Prerequisites

• Java 17
• Maven 3.9+ (or a compatible recent Maven)
• Docker (only needed for running the local HTTP server used by tests)

How To Use

Setup

• Compile first:

mvn compile

• Generate test files of various sizes:

java -cp target/classes cli.TestFileGeneratorCLI ./test-files

Default generated files:

• test-1024B.bin
• test-65536B.bin
• test-1048576B.bin
• test-10485760B.bin
• test-104857600B.bin

You can also specify custom output directory and file sizes:

java -cp target/classes cli.TestFileGeneratorCLI ./test-files <output_dir> [size_in_bytes...]

The content of the files will be pseudo random, and the used seed depends on the file name.

• Start a local HTTP server pointing to the test files:

docker run --rm -p 8080:80 -v ./test-files:/usr/local/apache2/htdocs/ httpd:latest

Downloader CLI

Run:

java -cp target/classes cli.DownloaderCLI <url> <output_path> [threads]

Examples:

java -cp target/classes cli.DownloaderCLI http://localhost:8080/test-1048576B.bin ./downloads/file.bin
java -cp target/classes cli.DownloaderCLI http://localhost:8080/test-1048576B.bin ./downloads/file.bin 4

Unit Tests

Run tests:

mvn test

The tests expect the server to be started with Docker as specified above and default generated files in the test-files directory. The sizes and contents of the files will be checked by tests.