How Can Java Generate a Relative Path from Two Absolute Paths?

Using Java to Construct Relative Paths from Absolute Paths

When working with file paths in Java, it can be necessary to create a relative path from two absolute paths. A relative path defines a location relative to a base path. This can be useful for simplifying file operations and traversal.

Question:

Given two absolute paths:

/var/data/stuff/xyz.dat
/var/data

How can you create a relative path that uses the second path as its base? In this example, the expected relative path is ./stuff/xyz.dat.

Answer:

One method to construct a relative path in Java is to leverage the URI class. The URI class provides a relativize method that performs the necessary checks and calculations.

Here's how you can use the URI class to create a relative path:

String path = "/var/data/stuff/xyz.dat";
String base = "/var/data";
String relative = new File(base).toURI().relativize(new File(path).toURI()).getPath();
// relative == "stuff/xyz.dat"

In this example, the relativize method takes two URI objects representing the absolute paths and returns a new URI object representing the relative path. The getPath() method is then used to extract the relative path as a string.

Additional Note:

For file paths specifically, Java versions 1.7 and above provide the java.nio.file.Path#relativize method, which can be used to calculate relative paths directly between Path objects. This may offer a more optimized approach for working with file paths.

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