How to Access Files from a JAR and User-Defined Directory in Java?

Creating a Java File Instance from a Resource

One can encounter a situation where files need to be accessed from both a JAR file and a user-defined directory in Java. To achieve this, it's essential to find a consistent method for performing the following tasks:

a) Loading files as streams
b) Listing files from the user-defined directory or JAR directory

Initially, using java.io.File was considered, but it's often preferable to avoid it in these scenarios. Therefore, the ideal approach is to load a directory from the classpath and list its contents.

Using ClassLoader to Resolve the Issue

The issue can be resolved using the ClassLoader class, which provides access to resources located within a JAR file. By utilizing the getSystemResource() method of ClassLoader, a URL referring to the specified resource can be obtained.

This URL can then be converted into a File object using File(URL.toURI()), allowing access to the resource as if it were a regular file.

Example Code

The following code snippet demonstrates how to load a directory as a resource and list its contents:

// Load the directory as a resource
URL dir_url = ClassLoader.getSystemResource(dir_path);

// Turn the resource into a File object
File dir = new File(dir_url.toURI());

// List the directory
String files = dir.list()

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