Question

I have a project which depends on several 3rd party libraries, the project itself is packaged as a jar and distributed to other developers as a library.
Those developers add the dependencies to their classpath and use my library in their code.

Recently I had an issue with one of the 3rd party dependencies, the apache commons codec libary,
The problem is this:

byte[] arr = "hi".getBytes();
// Codec Version 1.4
Base64.encodeBase64String(arr) == "aGk=\r\n" // this is true

// Codec Version 1.6
Base64.encodeBase64String(arr) == "aGk=" // this is true

As you can see the output of the method has changed with the minor version bump.

My question is, I don’t want to force the user of my library to a specific minor version of a 3rd party library. Assuming I know about the change to the dependent library, is there anyway in which I can recognize which library version is being included in the classpath and behave accordingly? or alternatively, what is considered to be the best practice for these kind of scenarios?

P.S – I know that for the above example I can just use new String(Base64.encodeBase64(data, false)) which is backwards compatible, this is a more general question.

Answer 1

package stackoverflow;

import org.apache.commons.codec.binary.Base64;

public class CodecTest {
    public static void main(String[] args) {
        byte[] arr = "hi".getBytes();
        String s = Base64.encodeBase64String(arr);
        System.out.println("'" + s + "'");
        Package package_ = Package.getPackage("org.apache.commons.codec.binary");
        System.out.println(package_);
        System.out.println("specificationVersion: " + package_.getSpecificationVersion());
        System.out.println("implementationVersion: " + package_.getImplementationVersion());
    }
}

Produces (for v1.6):

'aGk='
package org.apache.commons.codec.binary, Commons Codec, version 1.6
specificationVersion: 1.6
implementationVersion: 1.6

Produces (for v1.4):

'aGk=
'
package org.apache.commons.codec.binary, Commons Codec, version 1.4
specificationVersion: 1.4
implementationVersion: 1.4

So you could use the package object to test.

But I would say that it’s a bit naughty for the API to have changed the way it did.

EDIT Here is the reason for the change – https://issues.apache.org/jira/browse/CODEC-99.