How to resolve relative URI in Java?

Java 

This code will resolve the relative base uri e.g. if current base uri is /path1/path2 then ../path3 will be resolved as /path1/path3.

public class RelativeUriExample {

    //e.g. currentUri => p/xyz/abc   targetUri => ../stu =>  p/xyz/stu
    public static String resolveRelativeUris(String currentUri, String targetUri) {
        if(targetUri.startsWith("/")){
            return targetUri;
        }

        String uri = targetUri;

        while (uri.startsWith("../")) {
            int i = currentUri.lastIndexOf("/");
            if(i==-1){
                break;
            }
            currentUri = currentUri.substring(0, i);
            uri = uri.substring(3);
        }

        return currentUri + "/" + uri;
    }

    public static void main(String[] args) {
        resolve("/a/b/c/d", "../../e");
        resolve("a/b/c/d", "../e");
        resolve("a/b/c/d", "e");
        resolve("a/b/c/d", "/e");
        resolve("/a/b/c/d", "/e");

    }
    private static void resolve(String current, String relative){
        String s = resolveRelativeUris(current, relative);
        System.out.printf("current:%s target:%s resolved:%s%n", current, relative, s);
    }
}

Output

current:/a/b/c/d target:../../e resolved:/a/b/e
current:a/b/c/d target:../e resolved:a/b/c/e
current:a/b/c/d target:e resolved:a/b/c/d/e
current:a/b/c/d target:/e resolved:/e
current:/a/b/c/d target:/e resolved:/e

Alternatively, we can use java.net.URL as shown in the following example

public class RelativeUriExample2 {

    public static void main(String[] args) throws MalformedURLException {
        resolve("/a/b/c/d", "../../e");
        resolve("a/b/c/d", "../e");
        resolve("a/b/c/d", "e");
        resolve("a/b/c/d", "/e");
        resolve("/a/b/c/d", "/e");
    }

    private static void resolve(String current, String relative) throws MalformedURLException {
        String s = "http://base" + (current.startsWith("/") ? "" : "/");
        URL base = new URL(s + current + (current.endsWith("/") ? "" : "/"));
        URL r = new URL(base, relative);
        String result = r.toString().substring(s.length());
        System.out.printf("current:%s target:%s resolved:%s%n", current, relative, result);
    }
}

Output

current:/a/b/c/d target:../../e resolved:/a/b/e
current:a/b/c/d target:../e resolved:a/b/c/e
current:a/b/c/d target:e resolved:a/b/c/d/e
current:a/b/c/d target:/e resolved:e
current:/a/b/c/d target:/e resolved:/e