Groovy is a dynamic language on top of the Java platform. The strength of Groovy is that you can mix Groovy and Java language really well. So, you can take advantage of the metaprogramming capabilities of a dynamic language, however, you are building on your skills and strengths you already have as a Java programmer. So, instead of learning an entirely new language, it feels like your language has been extended. Scalability is subjective. You can use Groovy to gain speed in development. Depending on what you are trying to do you can gain good performance using Groovy or mixing it with Java as appropriate.
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Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop