Get a Path to a Resource in a Java JAR File

1. Introduction

Resources within a JAR file are typically accessed using a path relative to the root of the JAR file in Java. Furthermore, it’s essential to understand how these paths are structured to retrieve resources effectively.

In this tutorial, we’ll explore different methods to obtain the path to a resource within a Java JAR file.

2. Getting URL for Resource Using Class.getResource() Method

The Class.getResource() method provides a straightforward way to obtain the URL of a resource within a JAR file. Let’s see how we can use this method:

@Test
public void givenFile_whenClassUsed_thenGetResourcePath() {
    URL resourceUrl = GetPathToResourceUnitTest.class.getResource("/myFile.txt");
    assertNotNull(resourceUrl);
}

In this test, we call the getResource() method on the GetPathToResourceUnitTest.class, passing the path to the resource file “/myFile.txt” as an argument. Then, we assert that the obtained resourceUrl is not null, indicating that the resource file was successfully located.

3. Using ClassLoader.getResource() Method

Alternatively, we can use the ClassLoader.getResource() method to access resources within a JAR file. This method is useful when the resource path is not known at compile time:

@Test
public void givenFile_whenClassLoaderUsed_thenGetResourcePath() {
    URL resourceUrl = GetPathToResourceUnitTest.class.getClassLoader().getResource("myFile.txt");
    assertNotNull(resourceUrl);
}

In this test, we’re employing the class loader GetPathToResourceUnitTest.class.getClassLoader() to fetch the resource file. Unlike the previous approach, this method doesn’t rely on the class’s package structure. Instead, it searches for the resource file at the root level of the classpath.

This means it can locate resources regardless of their location within the project structure, making it more flexible for accessing resources located outside the class’s package.

4. Using Paths.get() Method

Starting from Java 7, we can use the Paths.get() method to obtain a Path object representing a resource within a JAR file. Here’s how:

@Test
public void givenFile_whenPathUsed_thenGetResourcePath() throws Exception {
    Path resourcePath = Paths.get(Objects.requireNonNull(GetPathToResourceUnitTest.class.getResource("/myFile.txt")).toURI());
    assertNotNull(resourcePath);
}

Here, we first call the getResource() method to retrieve the URL of the resource file. Then, we convert this URL to a URI and pass it to Paths.get() to obtain a Path object representing the resource file’s location.

This approach is beneficial when we need to work with the resource file as a Path object. It enables more advanced file operations, such as reading or writing content to the file. Moreover, it offers a convenient way to interact with resources within the context of the Java NIO package.

5. Conclusion

In conclusion, accessing resources within a Java JAR file is crucial for many applications. Whether we prefer the simplicity of Class.getResource(), the flexibility of ClassLoader.getResource(), or the modern approach with Paths.get(), Java provides various methods to accomplish this task efficiently.

As usual, the accompanying source code can be found over on GitHub.