How to List Files Inside a JAR File in Java?

Question

How can I dynamically list all files inside a JAR file in Java?

File textFolder = new File("text_directory");

File [] texFiles = textFolder.listFiles( new FileFilter() {
       public boolean accept( File file ) {
           return file.getName().endsWith(".txt");
       }
});

Answer

This answer provides a detailed explanation of how to list files located within a JAR file in Java. We utilize the `java.util.Zip` package to achieve this, allowing for dynamic loading of resources such as images stored in the JAR.

import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

public class ListJarFiles {
    public static void main(String[] args) {
        try {
            // Get the path to the JAR file
            String jarPath = ListJarFiles.class.getProtectionDomain().getCodeSource().getLocation().getPath();
            JarFile jarFile = new JarFile(jarPath);
            // Iterate through entries in the JAR
            Enumeration<JarEntry> entries = jarFile.entries();
            while (entries.hasMoreElements()) {
                JarEntry entry = entries.nextElement();
                // Filter for image files
                if (entry.getName().endsWith(".png")) {
                    System.out.println(entry.getName()); // List image file names
                }
            }
            jarFile.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Causes

Need to read multiple resources from a JAR file without knowing their names beforehand.
Requirement to load images dynamically instead of hardcoding paths.

Solutions

Use the `java.util.jar.JarFile` class to read the contents of a JAR file.
Retrieve and filter entries based on desired file types (e.g., .png for images).

Common Mistakes

Mistake: Not closing the JarFile after use, leading to resource leaks.

Solution: Ensure you close the JarFile in a finally block or use try-with-resources.

Mistake: Failing to account for potential exceptions while accessing entries in the JAR.

Solution: Always include error handling to manage IOException.

Helpers

list files inside JAR
Java dynamic loading images
Java list resources in JAR
Java JarFile example