Apps can be distributed on various different services, websites, and other potential sources. RepositoryManager is designed to support an infinite amount of them. How does it do it?
A `SourceDownloader` is a Java interface used represent instructions for how to obtain an application from a given source, implementing an abstract class `BaseSourceDownloader`.
All SourceDownloaders must be registered using the `SourceRegistry` object, when registered they become "installed sources" and used by the server during repository indexing.
The following is an example of a SourceDownloader:
{% code title="ExampleDownloader.java" overflow="wrap" lineNumbers="true" %}
```java
@Component // Needed so the server knows to instantiate this object automatically
public class ExampleDownloader extends BaseSourceDownloader
{
@Autowired // Required to receive the registry object
private ExampleDownloader(SourceRegistry registry)
{
// ID, Name, Description
super("example", "Mysterious Source Downloader", "Downloads a bunch of stuff from somewhere!!");
// Register the downloader
registry.registerDownloader(this);
}
@Override
protected Request fetchFileInformation(InstalledApp app, Path archivePath, Path tmpDir)
{
Request request = ...
// Fetch source information for this source type
// AKA, do all the work to identify the file to download,
// then return a request for the file to be downloaded.
return request;
}
@Override
protected void processFiles(InstalledApp app, Path archivePath, Path tmpDir, Request request) throws IOException
{
// Process files for this source type
// AKA, download the file to tmpDir.
}
}
```
{% endcode %}
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