Maven/Retrolambda: how to detect dependencies on Java 8 classes

Question

Background:

We have maven-based java project, which targets JRE 1.7, but the source code uses lambdas, so we use retrolambda for transforming Java 8 source code to Java 7. Also we use StreamSupport backport library when we need streams, function.*, Optional, etc.

Usage of retrolambda involves configuring the project's both source and target language level to 1.8.

Everything works fine if there are no dependencies on java8 classes or methods (like java.util.stream.*, java.util.Optional, or methods introduced in java8 like Collection.forEach). If there are such usages then build passes, but it fails in runtime, when running under JVM of Java 8.

Question:

My goal is to fail the build in case when such dependencies exist. Is there any way of detecting dependencies on new Java 8 classes/methods in build-time?

I thought about 2 possible options, but I'm not sure whether either of them is doable:

1. Some kind of bytecode analyzer for detecting depdencies on predefined classes and methods. Are there such tools/maven plugins?
2. Lint (lint4j) rules. Not sure whether it's possible to detect dependency on class/method using lint

Answer 1

You can use the Animal Sniffer Maven Plugin for this. It allows you to check that your code only uses APIs from a specified baseline (called the "signature"). In your case you'd use the org.codehaus.mojo.signature:java17:1.0 signature.

As others pointed out, you also could set up the bootstrap classpath, but that a) requires a JDK 7 to be set up and b) makes the build a bit more complex as you need to point to the JDK 7 install. Animal Sniffer is is much easier to work with in my experience.