File cryptedFile = ...
File destFile = ...

try(InputStream is = L2Crypt.getInputStream(cryptedFile);
	OutputStream os = new FileOutputStream(destFile)){
	byte[] buffer = new byte[0x1000];
	int r;
	while ((r = is.read(buffer)) != -1){
		os.write(buffer, 0, r);
	}
}

<repository>
    <id>jitpack.io</id>
    <url>https://jitpack.io</url>
</repository>

<dependency>
    <groupId>com.github.acmi</groupId>
    <artifactId>l2crypt</artifactId>
    <version>1.3.3</version>
</dependency>