section-3.md

Downloader Application

We are going to implement a simple downloader.

In this applcation, we can download multiple resources at the same time. But with a limitation.

The limitation is that we can download at most N files simultaneously. For example, if N is equal to 3, we can download 3 files at the same time. Then, when one of the threads has completed downloading a file, another thread will start its process.

Phase 1

You don't have to implement "download" part. Use Thread.sleep(500) instead to simulate the download opeartion.

Inputs

• MAXIMUM_PERMITS: The maximum number of downloaders that can download at the same time.

Implementation

The DownloadManager should take a semaphore, URL, and the output file name.

Use logging to record each operation performed by your threads. Add the following dependencies to your pom.xml file:

<dependencies>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>1.4.11</version>
    </dependency>
</dependencies>

Use logger in your class:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ClassName {
    private static final Logger log = LoggerFactory.getLogger(ClassName.class);

    public void foo() {
        log.info("Hello World");
    }
}

Parametrize your log:

public class ClassName {
    ...

    public void foo() {
        String threadName = "Thread-1";
        String url = "https://picsum.photos/200/400";
        log.info("{} started with url: {}", threadName, url);
    }
    
    ...
}

Phase 2

Implement the actual code for the "download" part to download the resources.